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Vorshlag C5 & C6 Corvette Development + NewBalance and Rampage

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  • Vorshlag C5 & C6 Corvette Development + NewBalance and Rampage


    This thread is now merged from three different C5 & C6 Corvette development threads. There was so much cross-over among these 3 threads that it became easier to merge them and update them all here. Sorry for any confusion!

    Project Introduction - March 26th, 2021:
    We just bought a 2006 Corvette for Amy to use to at autocross, on track, and on the street. This will be a rules-free build that will be done on a "normal" budget, with an emphasis on both streetability and great on-track manners. While this car might see some use in autocross or time trial, it will NOT be built strictly for those purposes or around any given rule set. Just a "fun buggy" that serves as a back-up car for when our main race cars are down that can actually be driven to events.

    And here it is in all of its 16 year old, used car glory! This is a "narrow body" base model C6, with a 6-speed manual and 45K miles that we bought for $20K. It is bone stock and overall in 98% perfect shape mechanically and about 95% perfect visually. A squeak under hood, a few scratches, and the wheels have some road rash - all things that are easy to fix/replace with parts we had planned.

    Now many of you reading this are likely wondering - why wouldn't we buy a widebody Z06 or Grans Sport if you wanted to get a C6 Corvette for performance use?!? It came down to two things: First was cost. I looked at comparable mileage C6 Grand Sports were more than double ($43K+) and low mileage C6 Z06 cars were higher still ($50K+). I found only higher mileage (usually 120K+) narrow body C6 cars for the same or more costs, and 100% of those were automatics (yuck). It was an easy purchase that we could get on track immediately.

    Second was: low stress. This C6 being a less desirable "narrow body" means we won't be as inclined to "go crazy" and build some wild race car (plus I already have an all carbon widebody C6 Z06 in storage, waiting for a complete build, above). As a relatively low value C6 we won't stress out if it gets a scratch or a tiny bit of cosmetic damage. I try to explain further why we went this route below...


    Vorshlag started out 16 years ago developing parts for the most flawed cars, and our unofficial motto was "We make your car SUCK LESS." The more terrible the OEM suspension, the more improvement we could offer! Most sporty car models then (as now) were built with McPherson strut suspensions, soft spring rates, inadequate roll stiffness, skinny wheels and tires, and all sorts of other performance compromises.

    This is where we started.... strut suspension cars

    We started out with BMWs and Subarus as the primary targets of our parts development, and that method of attacking the "low hanging fruit" has paid off for the business. I am glad we went that direction, instead of chasing true sports cars that came with MUCH better stock suspension options. And in extreme cases we even swapped in LS engines, which I first stared doing in 2002.

    Cars with terrible suspension are easy to make big improvements on!

    But the year before we started Vorshlag (2004), Amy walked into a GM dealership to look at the then brand new C6 Corvette. This was just days after the new generation Corvette hit the streets, and it was a radical departure from the C5 generation before it (which neither of us liked, since the C5 is the Corvette with Four Asses). She saw a new C6, fell in love, and custom ordered a 2005 Corvette Z51 6-speed in silver. It arrived a few weeks later. It came from the factory with decently wide wheels, world class suspension, and LS2 power - with a 186 mph top speed in stock form.

    This was our 2005 C6 Corvette Z51 - which we ordered new in 2004

    This was her first new car purchase and it was just an amazing car, which she loved. We both autocrossed it a few times (after several years away from that sport) but mostly she drove it to work and loved every minute of it. I hooned it a bit... took it to Houston Raceway Park and ran the 1/4 mile (12.8@112), weighed it on a scale, dyno'd it (355 whp). The wheel offsets needed proved to be a challenge so I bought some 17x11" C4 ZR1 rears and we ran 315/35/17 Hoosiers, which poked like crazy!

    We sold our 2005 Z51 to help pay for a new home + shop, to concentrate on starting Vorshlag in 2005

    But in 2005 when we had just started Vorshlag and had some tough choices to make. Keep a relatively expensive new car / note ($45K) while building an expensive new home with giant attached shop (which we ran Vorshlag out of from 2006-11)? A car we would have trouble applying our Vorshlag fixes to? It did not help the business, and it was a tough choice, but we sold it after 1 year - to a dealer, who paid us sticker price - because NOBODY could get C6 models at the time, and our rare Z51 6-speed no option car was SUPER rare at the time (90% of early C6 models are automatics).

    My main track car (S550 Mustang) was sold. Amy's FR-S is being LS swapped and stuck behind customer cars

    Fast forward 15 years, and after many years of having multiple track and autocross capable cars at any given time, 2020 was a bleak year for racing in the Fair household. We sold my 2018 Mustang (above left) in August 2019 to move onto a more serious S550 race car build, but that stalled out with manpower limitations in our shop and a customer car build backlog. Likewise Amy's 2013 FR-S (above right) was pulled from racing duty in late 2018, but the LS swap work on that car stalled out for the same reasons. So Amy and I haven't raced anywhere in our own cars going on two years! Neither of us like borrowing cars either. We're both going stir crazy NOT competing track or autocross events.

    I have been bumming co-drives for a year in a friend's C5 we used for development

    At an event at Eagles Canyon Raceway a week ago (above), Amy was lamenting our "stalled out" race car builds and declared - "It is time to buy another car, that runs, that I can race RIGHT MEOW." We puzzled over a few ideas while in the drivers lounge with some friends, and Jason here at Vorshlag mentioned this 2006 Corvette he had for sale... Yadda, yadda, yadda.... she bought it!

    Of course, every car we buy for the business has to "earn its keep" here at Vorshlag. 16 years after starting Vorshlag and we are indeed developing parts for more than just "Crappy McStrut" suspension cars. We have even had some success with our products developed for the C5 platform, among other non-strut cars.

    For this narrow body C6 have a small budget for this one, and overall build will be fairly mild - we want to keep this a 100% street legal, nice driving car *that is also track capable* and quick. Goals do NOT include TT track records or some SCCA obscure autocross class rules - just an all around "fun buggy" that she can run "where it fits".

    While Vorshlag is not known as a "Corvette Shop", we still make a number of unique parts for some Corvette models and have worked on a number of C4, C5, C6, and C7 Corvettes over the years (and I have personally owned 5 Corvettes - two C4s and three C6s). For this narrow body C6 there are a number of areas we can improve with our part solutions - which we will prove with track testing, data, and product development.

    Initial plans for this car include the usual Vorshlag upgrades: custom wheels and wide 200TW tires, MCS non-remote coilovers, G-LOC pads on fresh Z51 rotors, adjustable swaybars, maybe seats, and of course a number of new C6 specific "track products" from Vorshlag. We will share the development of the car and these parts in this forum build thread, of course.

    I have driven numerous C4, C5, C6 and C7 Corvettes at Motorsport Ranch on their 1.7 mile CCW course

    Will get a baseline lap in stock form at two race tracks: MSR Cresson and/or ECR. Having driven 500+ laps at MSR in dozens of cars and 1000 laps at ECR (on the old 2.9 mile layout), with dozens of wins and class track records in Time Trial at both locals, these tracks will be best suited for our initial and continued testing on this C6.

    Baseline laps will be done with just with fresh Motul RBF600 brake fluid and stainless brake lines (which the C6 already has). We will go back after each major round of parts changes to chronicle any lap time gains or losses. To help with this testing we purchased a membership at Motorsport Ranch and a membership at Eagles Canyon is coming shortly.


    On March 25th, 2021 we put the new C6 on the lift for the first time to take a look at the car more closely. Brad wiggled all of the bushings, wheel bearings, noted any leaks or issues. First things we noticed that needed replacement: idler tensioner pulley, engine mounts, oil pan has a slight leak, hood lift struts were shot, and I wanted to do a full oil & filter replacement. We will also swap in fresh plugs (NGK TR6), plug wires (Taylor 10mm), and plug wire heat boots (DEI).

    We also, of course, got an initial weight. And it was a pleasant surprise, and a relief after dealing with 3600 pound pony cars for the last fee years.

    Ideally I like to weigh a car with the fuel tank as empty as possible. This makes it is easier to compare car-to-car weights. Why empty and not full? Because we almost NEVER autocross or track a car on a full tank, but have done those events with low fuel levels (There is no such thing as "good ballast weight"). We run the least amount of fuel needed for the session and/or to prevent fuel starvation. But this one had 5/8ths of a tank when we bought it, and we didn't have a lift clear for very long so we took the weight we could get.

    Now my memory of our 2005 Z51's weight was 3148 lbs, which I weighed at a drag strip in 2005 - but that was 16+ years ago, before we really started Vorshlag, before we owned our own digital scales, and before I began documenting EVERY weight on EVERY car we owned or worked on. Plus, that 2005 Z51 had bigger brakes and wheels than this 2006 "base" car, so maybe that makes up for some of the weight difference? Or maybe my memory isn't 100%...

    continued below
    Last edited by Fair!; 11-10-2023, 05:06 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev

  • #2
    Project Introduction - April 10, 2014: This was originally a build thread for a customer's C5 Corvette, Mark Council, which morphed into a C5 Development Thread. I normally I won't make a "Vorshlag Build Thread" for every customer's car we work on, but this one is a bit special. Mark is testing out some new things we're either making, sourcing, or selling. On top of that he let me race his C5 at Optima already and I will likely take laps in testing in the future.

    Picture above is from an autocross in August 2016

    This 2002 Z51 6-speed Corvette was being built as a "track rat" that (for the moment) can still be driven to a road course, but with few other considerations (and he's already truck / trailer shopping, so that requirement may go away soon). It later turned into an autocross only build. Initially Mark was just looking at getting some wheels and a few things repaired, but his car came to our shop at a time when I needed a car to drive at Optima... so we worked out a deal and this C5 became a bit of a test bed for us to try some new parts.

    We met Mark at the May 2013 NASA event at NOLA Motorsports Park, where he was autocrossing with the local SCCA

    I met Mark in May of 2013 at NOLA Motorsports Park (above) when we were racing with NASA down there. It was a crazy weekend, my first time to run that track in anger and ended up being one of my strongest finishes of the year, obliterating the TT3 record and outpacing all but one TT car that weekend. Mark was there to autocross with the local SCCA region and convinced me to come do some fun runs with them on one of the dedicated autocross pads at NOLA. It was only about 200 feet from our paddock spot, and Mark rode though to navigate and show me the course - where we set the fastest autox time of day in our TT3 road course set-up with zero changes, heh. Crazy weekend where all the stars aligned.

    Mark's 2012 Mustang has been modified for autocross and track events, but he wanted more than this chassis could deliver

    Mark had already purchased some 18x10" race wheels and some other bits from us, but after that NOLA event he worked more closely with us to get more parts and work done at our shop to his 2012 GT that transformed it from daily driven commuter to a real autocross and track terror. He took it pretty far down the autocross path, then realized... it was always going to be a stick axle Mustang. What's better than even a great set-up S197 pony car? A Corvette! Well... maybe we pointed him in that direction, who's to say? He also wanted a "dedicated track car" and is looking at a "dedicated autocross car" using another chassis, which we might build for him also. That thing... well, I can't talk about it yet.

    Here are a couple interior pics of his 2002. Brey-Krause harness bar, Scroth harnesses, Sparco EVO II seats are nice.

    Mark got a great deal on this silver-ish 2002 C5 Corvette "fastback" (non-FRC/non-Z06) in early 2015 that already had some good parts on it (headers, Sparco seats, Schroth harnesses, B-K harness bar) and a few not-so-great parts (Konis, Borla sound amplification unit, very grabby clutch, and a piss-poor engine tune).

    Borla exhaust is going away soon (left) but the engine bay has some nice parts (right) like a Ram Air set-up, full length headers and a cam

    He started a build thread on the Corvette Forums located here and I'm sharing more of the work we do on this Vorshlag Project Build Thread. Our thread is posted and will be updated on these forums:
    Why is the C5 Important?

    The answer is simple: the C5 generation Corvette is probably the best bang-per-buck track car in the world right now. Nothing else can match this car's factory road course performance, suspension, horsepower, brakes, and low aero drag of the C5 considering the used car prices they are selling for right now ($12-25K+). That's a bold statement, I know, but its the truth. And while we've been able to beat most C5s in the same NASA power-to-weight class with our TT3 Mustang, we had to go pretty hard core to do that (345mm Hoosiers, massive aero, high end suspension mods and brutal drives).

    Left: Aluminum subframe and composite springs are unique to the Corvette. Right: Look at the frontal area compared to this S197 Mustang!

    The C5 was a pretty radical departure from the C4 chassis, but they share a lot of the same roots. Very low center of gravity, good front-to-rear bias, composite bodywork, low drag aerodynamics, but also a small-ish cabin that can be a challenge to add a roll cage to or to fit around taller drivers. The GM "Y-body" chassis is a halo car program shares it's chassis with no others (we will ignore the "Cadillac thing" that was based off the C6), and it is very nicely priced when new compared to its peers - the Viper, the 911, and a few others. And like I said, used prices on the C5 and C5 Z06 are astonishingly low right now. But finding a clean, unmolested C5 Z06 is getting more difficult and prices have started to go up a tick. So Mark skipped the Z06 and FRC models for the lower cost, more abundant, and swoopier Fastback Coupe.

    The C5 (1997-2004 model years) moved away from the short-lived Gen II "LT1" family of engines to the all new Gen III "LS1" engine, which was revolutionary in many aspects (and still extremely popular today). The ZF S6-40 6-speed manual of the later C4s was also tossed in favor of the Borg Warner (now Tremec) T56, which was 25 pounds lighter, quieter, and performed as well or better than the ZF. The C5 also was the first Corvette to get a hydroformed steel frame, which was much more rigid than the welded sateel frame on the outgoing C4, and massively cut down on squeaks and rattles. It also got the first Corvette rear transaxle, where the transmission and differential are housed behind the driver. This improved weight bias to 50/50. It also is unique in that it came in 3 distinct body styles: fastback, fixed roof coupe and convertible. A total of 248,715 C5 Corvettes were built from 1997-2004, so there are plenty out there to choose from.

    The "Fixed Roof Coupe" C5 (at left) may be a hair lighter, but the "fastback" Coupe (right) has cleaner aero at speed

    This C5 "fastback" body shape is advantageous over the FRC/Z06 trunk shape at higher speeds, so that's a plus. The prices on good Z06s have gone UP lately and the best parts of a Z06 would be replaced on a build like this anyway (cam, intake, exhaust, springs). It is actually a bit harder to find a fastback with a 6-speed manual, but there are cost advantages when you do find them, and the weight differences are almost a wash. The lightest I've ever weighed a stock C5 Z06 was 3048 pounds with zero fuel (and the OEM titanium exhaust) and this one came in at 3114 pounds with 1/4 tank. So its... about 40 pounds heavier? That's not a lot. The C6 was 3150-3300 while the C7 has ballooned up to 3400-3500 pounds (depending on model and options). The 2011-14 Mustang that Mark is leaving was 3600 pounds in stock form and the latest IRS S550 chassis Mustang is 3750-3800!

    And while Vorshlag isn't "known" for Corvettes, we have worked on quite a few, and I personally owned and raced several C4-C6 Corvettes (see above) in my early Vorshlag days. I respect this chassis immensely, and my only hang-up with the C4/5/6/7 chassis in the past was that they handled SO well out of the box, it was hard to make them a LOT better than stock (not like we can do with McStrut cars). But after driving Mark's C5 car in the Optima 2 day competition, I noticed it is in fact easy to make them handle WORSE than stock with the wrong parts, heh.

    Not to mention we have gotten pretty far ahead of the "stock handling" and road course performance with our NASA TTC/PTC classed, 1992 C4 Corvette (Project #DANGERZONE, shown above) that I am racing this year, and a lot of the same principles can be applied to this C5. Upping the spring rates in the right proportions, install better dampers, change out rubber bushings, lower ride height/CG, add power, and add wheel and tire width. Plus improve brake pads, brake fluid and brake cooling. Then develop some downforce with it, using the right techniques and parts. So yea, maybe we can make a C5 significantly better?

    More tire, more downforce, more spring, more damper.... its a proven formula, if you know what parts to use or how to build them

    And that's pretty much what we have planned for Mark's car. Shocks, spring rate, bushings, wheels/tires, aero, a better engine tune, and a quieter yet higher flowing exhaust. We will use some off-the-shelf parts, some "tweaked" parts, and maybe a few all-new designs. The Corvette aftermarket is pretty crowded, for sure, but there's always room for "a better mouse trap". I don't want to make "me too!" parts, something just to mimic everyone else's existing upgrade options, and if someone else makes the best part that we cannot top, we will use that. Otherwise... we have engineers, fabricators and machinists on staff.

    We have the tools.... we have the technology...

    continued below
    Last edited by Fair!; 09-03-2016, 03:55 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


    • #3
      Re: Mark C's 2002 C5 Corvette - Track Rat

      continued from above

      What bothers me a little about the Corvette aftermarket is that a good number of the common Corvette upgrades are Chinese built parts. That's a dirty little secret a lot of vendors don't like to talk about, but we won't be using any of that on Mark's C5, for sure. Stay tuned to see what we put together... We will share what we learn along the way, any race reports which we attend and/or drive Mark's car, and lots of pictures and video. Should be a fun ride when we get done!

      First Round of Mods & Repairs

      After Mark purchased this C5 he knew it needed some help, so I drove 2.5 hours to meet him and picked it up in early March in our enclosed trailer. At that time our shop was utterly slammed with customer work. And well... we are usually booked 2-3 months out for big jobs like this, but we at least squeezed it in for a couple of days to do some initial measurements and then some small repairs before I ran it at the Optima event March 28-29th.

      I am weary of all "internet" measurements, so when we decided to spec a new set of Forgestar wheels for this car, we took all of the measurements ourselves of the hub diameters (above left), existing TSW 18x10.5" wheels (shown above right), and then measured the room inboard and outboard at the front and back with those wheels and tires.

      The somewhat heavy-ish TSW wheels were already rubbing on the front upper and lower control arms at full lock, but we noted this mostly happened at full droop, which is an unusual situation.

      We took that data and looked at a lot of other situations for ride height, suspension travel and steering angle and came up with an 18x11" wheel spec that fits both ends of the C5. We then sent a rushed order to Forgestar for a custom set to be built with no powder coat (to save time; we will powder coat these few weeks later). Wheels with the same specs can be purchased through Vorshlag.

      Left: Forgestar CF5 powder coated black with a flat clear coat. Right: The raw (and dirty) 18x11" CF5 weighed in at 23.1 pounds

      Mark wasn't ready to minitub (for 19x12 rears) or flare the car just yet, so we went with the widest wheel and tire package we could fit under the stock fender limits while keeping it 18" diameter (for better tire choices and a more favorable sidewall). We do a lot of custom wheels with Forgestar and the F14 and CF5 are two of our favorite 1-piece rotary forged wheels they make. This company is unique in that they keep a lot of semi-finished wheel blanks in stock, then cut the backspacing, hub bore and bolt circle for all custom orders. After they are powder coated they usually ship out in 3-6 weeks from their California facility. The 14-spoke Forgestar F14 (18x12" are shown on my Mustang, below) is usually 1-1.5 pounds lighter than the CF5 in these sizes, but Mark wanted the easier-to-clean 5-spoke CF5 design, plus the CF5 has a different barrel that will clear a larger 385mm diameter brake rotor (15").

      The tires we used on the C5 were just what we could scrounge up at the last minute before this Optima event. The C5's rears were some 315/30/18 BFGoodrich Rivals that I ran on the front of my 2011 Mustang at this same event last year (where I won overall, surprisingly). This pair had been used there at Optima, later in about 2 other autocross events, but then sat in our climate controlled shop since we moved to 335s at all 4 corners for this Mustang, after the Texas Optima round in 2014. The front tires for the C5 were a pair of very worn 295/35/18 Rivals that a customer gave us, a size which cannot be purchased for any amount of money (they've been on backorder for 5+ months). If we were taking this Optima event more seriously we.... well, there wasn't much out in 200+ treadwear at the time that would fit or be worth using. There's a serious drought of tires in this performance and size range, but hopefully by the end of April this shortage will be over. The Rival and Rival-S should both be back in stock by then, we hope?

      As you can see these "they run large" BFG Rivals are pushed to the limits of the fender contours at both ends, and they cannot go inboard more than 3mm without touching something, either. So I will say something somewhat definitive: an 18x11" wheel is as wide as you can go on a C5 without mini-tubs or flares, unless you can live with some "poke" past the fenders (that is something I cannot stand). Even just a 10mm wider tire at the front would have poked past the fenders, but as it turned out this 295/315 combo was the perfect size front and rear tire for this wheel and chassis. Sometimes we measured and guess well.

      If the images look blurry and bad, I probably took them with the #potatocam on my phone

      The other work we did to the C5 before Optima was just some simple repairs, like the rear axle seal (1.77 hours) that was leaking at the transaxle. There was a tiny ring of wear on the halfshaft but the leak hasn't returned, so that's good.

      Last but not least we freshened up the brake system a bit. The old pair of front 2-piece Stoptech rotors were done, so they were replaced with C5 Centric Premium rotors (see below left) - which we will begin stocking and selling. The rear rotors were just a tick worn and were turned then re-installed. The front pads were done but Mark had a brand new set of Hawk HP+ pads that came with the car that he wanted us to use.. which turned out to be a terrible mistake, especially not knowing what the rear pads were (we think now they were a more aggressive Hawk DTC compound). I should have trusted my gut and purchased a new set of Carbotech XP20 pads for both ends - live and learn.

      Replacement StopTech front rotor rings were on national backorder, so some cost effective Centric Premium front rotors went in their place

      The brake fluid looked like coffee, so it was flushed and replaced with fresh Motul RBF600, our go-to brake fluid for a track or autocross car. A quartet of Alcon temperature indicator strips were added to the calipers, for a bit of data. The oil was replaced with a fresh batch of Mobil1 15W50 synthetic (run +1 quart over full, for track use) and a Wix 51042 oil filter.

      Last but not least we checked the corner weights with the new wheels and tires attached. The 3114 weight with 1/4 tank of 93 octane fuel was good, but under the 3200 pounds (without driver) needed to run Optima's GTS class, so we filled the fuel tank for this event plus hid a little ballast on board in a safe place. A little cleaning, some decals, and off we went to the Optima 2-day competition!

      What's Next?

      I'm short on time and my post is running long, so I will save the race write-up of the Optima Street Car qualifier March 28-29th for next time. Now all we really had prepped on the car was the wheels and tires, plus a few basic repairs. The brakes were questionable and we knew it had some other issues, but I figured, "hey, I've been doing this a while,I can 'drive around' whatever issues it has!" Famous last words, heh. This USCA/Optima event was a televised 2-day competition that had 5 segments that included an autocross, speed-stop and road course time trial. The C5 had some issues and stopped, turned and launched for crap, but I managed to limp the car onto the GTS class podium.

      I will share all of the lessons learned from this brutal competition that turned into a "test day" in my next post. We also have some proper upgrades planned that somehow Mark has signed off on. Big suspension upgrades, a new rear exhaust layout unlike anything I have ever seen on a C5 to date, proper brake pads/cooling, and some aero mods that border on "Full Retard".

      Last edited by Fair!; 11-28-2017, 05:48 PM.
      Terry Fair -
      2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
      EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


      • #4
        Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

        Project Update for May 20th, 2015: Long overdue race report for the March Optima @ TMS event is finally here. Also gong to show several modifications we've completed on the C5 and future plans.

        Since we made a tactical decision before entering Optima @ TMS to put Amy in the Mustang in their GT class, I borrowed Mark's C5 Corvette to run in their GTS class. This Optima event write-up will be in both the S197 Test Mule and the C5 Test Mule forum build threads.

        Corvette-less Forums?

        Just wanted to note that the original build thread Mark started (not me) on was recently locked, heavily modified, then outright deleted a few days later by the moderators there after our Vorshlag watermarked pictures got another vendor there all spun up and they pitched a fit. Frankly, any photographer worth his salt will watermarks their pictures - its just common practice. We have had a lot of our images stolen and used by competitors, claiming they were their own, so I started watermarking Vorshlag pictures almost a decade ago (and yet it still happens). I got a PM about the pictures from a moderator a day after the thread was locked and deleted, but it was pretty weak.

        Did a little research and quickly found that CorvetteForum is now owned by InternetBrands. I cut all ties with this organization after finding out first hand how shady they are. So long story short... this build thread is off of CorvetteForum, but you can read it on the other forums linked in my initial post. Thanks!

        March 28-29 - USCA @ TMS (200 treadwear 5 event Challenge)

        So my comments about prior USCA/Optima events have been all over the place, especially after the cluster-truck last November with the "OUSCI event" in Vegas after SEMA. I couldn't even post my review of that event, it went so far off the rails. This is a big series with all sorts of complications - a wide variety of cars, drivers of all skill levels, and various sponsor and TV obligations - and some rules I won't always agree with, but it is also televised and I can't ignore that for the potential exposure for our business. Fortunately they made a LOT of changes and improvements (new competition rules, timing equipment, and policy changes) in 2015 and it showed at this event back in March. Big improvements, and now the Optima series is back to the fun filled event I knew they could put on.

        Since there was a $3000 cash bounty on hand for "new Optima entrants" to win the GT class in a Mustang or Challenger (put out there by Camaro driver Ken Thwaits), we stuck Amy in our 2011 Mustang in that class. Why? Since I'd already run an Optima event before, I wasn't eligible, but I won this class in this car, and even against this particular driver. So since she had a shot at three grand, and she's a good autocrosser and licensed Time Trial competitor, we stuck her in big red. Jon from Vorshlag was also giving the $3000 cash prize a shot in his Legend Lime 2006 GT (above right) as well. Engineering intern Shannon (below right) was also entered in GT class along with her mother Jan, both driving in S197 Mustangs (but they ran Optima last year, so weren't eligible for the $3000 bounty).

        Since I wasn't going to be driving our Mustang I rented frequent Vorshlag customer Mark Council's 2002 Corvette (aka: the "eBay special") that I entered in the GTS class (above left). Neither Amy or I did all that well, but we still had a lot of fun and are both glad we went. There were a total of 11 entries from Vorshlag, from employees to customers, and we all had fun at this event. Remember that when reading my rants below - most of which were caused by the car I borrowed, which was untested and modified in weird ways. We've since fixed almost all of these ills, but we only had a few days before this event to repair some broken parts, and I took it with just a quick wheel/tire upgrade we put together.

        Funny thing happened - When I signed up the C5 Corvette in GTS class (for 2 seat cars + AWD cars, over 3200 pounds) there were only 6 in class and 5 were novices, and no AWD cars. This was only a week before the event. Well somehow the GTS class grew to 16 cars, with some cars moving up from GTL, and 7 of the late entries were AWD cars. Those types of cars compete exceptionally well at the standing start Speed Stop and Autocross events at Optima, especially the way that they set up their courses. That influx of late entry AWD cars was an unexpected surprise.

        This made winning the GTL class no longer "shooting ducks in a barrel", as some seriously fast AWD cars were now balanced between GTL and GTS class, with some hot C6 Z06 entries in both of these classes as well. The 4 seat, 3200+ pound GT class was also stacked, and the vintage class (GTV) had some of the nation's top Goodguys competitors. There would be no easy wins this weekend!

        Overall Results from Optima @ TMS: LINK

        Amy was always going to be fighting a tough battle, as the top 3 cars in the 26 car GT class were serious, dedicated race cars built only for ONE purpose: racing in the Optima series. Ryan Matthews' 5th gen Camaro (below) is prepped by Detroit Speed; its a gutted and caged race car with a big nasty motor, real aero (with a new spoiler and rear diffuser to meet the 2015 aero rules) and a pro driver in it. Ken Thwaits somehow entered two 5th gen Camaros into this event, who was formerly a pro driver as well. Both his 1LE and Z/28 have radical motors, the same 2015 aero work, good suspension, and more. These 3 cars were in a class to themselves, and it showed in the results.

        Let's just breeze past the fact that pro drivers aren't allowed to compete (rule 24), or that participants may not register more than one vehicle per event (rule 22). The rules in USCA are more like suggestions or guidelines. There's a movie quote in there, I think? After the things I've seen over the years, I have stopped getting worried about the rules at Optima events - makes for less stress.

        This event was a packed with 72 cars - a record for any USCA/Optima Qualifier event - but they handled the extra volume of entrants well. Compared to last year, where this TMS Optima event had but 32 cars (8 of which we brought), this was a nice improvement. Thanks go out to the Texas shops (Evo-D, Dusold Designs, Robert Jack's crew) and Texas racers who came out and entered and brought customers with them. Vorshlag brought the most entrants and they noted this several times during the event, but more importantly, Texas entries were a big percentage of the overall entry list - which is how these events are supposed to work.

        Brian Matteucci (above) is an old college racing buddy and fiend - who sold me the smoking C4 Corvette (project #Dangerzone) I've been running in NASA this season - was also there in one of his two blue C5 Z06 Corvettes. The car he brought this time was his "track rat" that he had recently purchased for NASA TT prep. This car came with a worn-out smoking motor, on its last legs, but with a fresh LS block already in line to be built by HKE. Brian did really well at this Optima event in GTL class, especially considering it was a bone stock C5 Z06. He is an experienced autocross and road racing driver, and he proved that "skill > parts" once again. His Z06 was running on 275mm Bridgestone RE71R tires, which don't suck but were significantly narrower than the 295/315s I had on the 2002 Corvette.

        I point out his times to show how badly the "eBay" Corvette I drove did in comparison. Brian and I have known each other and raced together for 25 years, and we have co-driven lots of cars together. Our driving styles and general times are usually very close, so keep that in mind when you see his Autocross and Speed Stop times in a stock C5 Z06 vs the times I was able to lay down in a "modded" C5, using a lot of parts that are "popular on the forums". I only bested him in the Hot Lap challenge, but that was because he only took like 6 laps, due to the excessive blow-by and smoke from his worn out motor.

        As I mentioned, another GT class competitor going for that $3000 bounty was Vorshlag's own Jon Beatty. His 2006 Mustang GT was on MCS TT2s, 18x11" Forgestars and some 295 Rivals - which is a package he uses to terrorize local autocrosses in CAM-T class (where he almost always wins).

        Vorshlag's Optima Event Gallery: LINK - pictures taken by Brad Maxcy, my S4's #potatocam, or from others posting on Facebook

        Doug Willie brought his "F Street" prepped 2013 Camaro autocross car to give this event a try also. Doug did really well and took 4th in the GT class autocross in a stock 2013 Camaro 1LE on skinny 285mm Hankook RS-3 tires (he was saving his 305 Hankooks for an upcoming National Tour). So once again skill > parts, at least in the autocross.

        So when it came to our two primary cars, Amy had to run the autocross in the morning Saturday while most of us ran the speed stop. She was shown in 2nd place at the autocross in GT class after the ~3 hours of morning runs, but as the course "rubbered in", the afternoon cars went much quicker and she fell down to 6th place in class (Jon got 5th while Doug got 4th behind the 3 race cars that swept the podium). Bummer. She had never done a Speed Stop event before but persevered and took a whopping 18 runs on that course (next closest was 13 runs). She scored her best time (10.9) on her LAST attempt, placing 6th in class for this event. The chances at that $3000 prize weren't looking good.

        And it continued to worsen as Amy's worst event in the Mustang was Sunday in the Hot Lap challenge (time trial), where she struggled to get 9th out of 26 in GT class on the road course. Why? Several reasons. She had never run the 1.1 mile TMS infield road course before, had never run this car on course with street tires and NO aero, and she said the car was WICKED loose. When all you are used to in your car for the past 3 years are 345mm Hoosier A6 tires and big downforce, it can be hard to adapt to no downforce and street tires. Lack of rear grip kept her cautious all day, but I was trying to motivate her and kept telling her to PUSH IT.

        Well she did push it, and on the opening laps of her 4th session on track (we all had 6 different 15 minute track sessions on Sunday) she spun it into the infield, shown in this short video, shot from Matteucci's C5 (with a potato for a camera, #potatocam). I couldn't get her to record any of her own video in the car but she managed to have one of the AiM Solo's that recognized this track, so she at least had lap times. And her spin was in good company, as Jon and Doug from our crew both had spins, and as you'll see below, so did I.

        It was a tricky, dirty track surface with ChumpCar running the day before. The track management had just added some tar repairs to cracks in the asphalt on the road course and parking lots, but in the heat those were coming up all weekend, making for lots of "OPR" stuck to your tires. It got so bad that it often felt like you'd thrown a wheel weight and people were coming in early to scrape it off. This was also an issue on the autocross, to a smaller degree.

        I fought the eBay Corvette all day Saturday in the Speed Stop then the Autocross event, cursing up a blue streak and even making up some new words. The Koni 3000 series dampers are way too long and only work at really TALL stock ride heights. With a 1/2" of lowering on the previously installed aftermarket spring bolts the car had virtually no rear bump travel (1/4"!) and would bottom out simply under acceleration, as well as whenever I hit any actual bumps or dips on course.

        Handling was flat TURRIBLE and the braking was a big hot mess as well. The Hawk HP+ front pads were overpowered by the racier (Hawk HTC?) rear pads that had been installed, and this threw the brake bias off so much that not even the C5's ABS could keep up with. This video is my 8th autocross run of 9 attempts, and one of the few where I managed to point it between the cones correctly. From the clutch to the shifter, brakes and handling, what a total MESS this car was. Of course it should have been tested before Optima, but as I wrote in my last C5 thread update, we didn't have the time to do any testing or change any significant parts. We ran what it had + the 18x11 Forgestar CF5 wheels we spec'd and had rush built, shod with some used 295F/315R BFGoodrich rival tires we had around the shop (Rivals were completely out of stock at the time, and this was the best we could come up with on short notice).

        Somehow, even in the worst handling car I've driven in a decade, the ebay Corvette still managed 3rd out of 16 in the GTS class for the Autocross, with AWD cars (unsurprisingly) in 1st, 2nd, 4th and 5th. That finish result was shocking knowing how slow I was compared to Matteucci in the stock C5 Z06. My best time was a 44.995 and Matteucci ran a 42.638, on stock sized wheels and 275 tires compared to my 18x11's and 295/315s. Yes, you CAN make a C5 handle worse than stock, to the tune of 2 seconds, if you choose the wrong parts. So this ended up being a good test, to show which mods to not choose.

        continued below
        Terry Fair -
        2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
        EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


        • #5
          Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

          Continued from above

          This C5 did have some good parts on it when Mark bought it (harness bar, seats, harnesses, headers) and the one thing we added helped (18x11's and bigger tires), but it was still full of what I call "eBay parts", the lowest cost options sold by shops that don't have hands-on experience.

          My perspective is that there is a lot of "group think" that comes from internet forums, some of which is led led by shops and parts sellers, but most of it by like minded folks. Because of a strange set of circumstances the worst parts available (the cheapest) end up being the ones most people buy. Why? Because people are convinced they need a lot of parts (many that don't really help) and they want the best deals. So a lot of folks end up buying the cheap option that everyone else recommends. They then shout about the new parts' positive qualities while ignoring the obvious problems, to help justify their purchase. This process is how low end parts are often touted as the best parts, without the buyer realizing the compromises inherent in them. "Most Popular" doesn't equal "Best". We see it in every market, and the Corvette world is no different. Sure, some folks know about proper dampers and choosing quality parts, but the racers at the front of the pack don't usually share their setup secrets as freely as the Internet Forum Experts. /EndOfRant

          In the end, all of the issues I noted in this car were created by a few upgrades that just didn't work well together or with the rest of the car. Some of these parts may work in some special circumstances, or with specific other parts. The Konis that were too long might work fine at bone stock ride heights; the cam that is too big and wrecks the power curve would probably work great in a bigger motor with more rev potential; something goofy happened in the tune but it could have been from a part installed after the previous shop programmed the ECU; a grabby twin disc clutch that made it impossible to launch smoothly is often needed at power levels much higher than this car has; and the loud flashy quad-tipped exhaust makes the car miserable to drive. The mis-matched brake pads that made the rear tires lock up were just a bad decision on my part - I should have insisted on a new set of pads be used at both ends, in a compound/brand that we trust, instead of using random stuff that came with the car. Honestly, a bone stock 2002 Corvette would have been faster than this combination of parts, and a damn sight easier to drive.

          The Saturday events also included the Design and Engineering challenge, which tends to have real "hit-or-miss" scoring on the judging. The 3 judges can spend anywhere from 2 minutes to half an hour on any given car. They are supposed to check off items from a list for "streetability", which accounts for 15 of the 25 points. Glass, interior/carpet, HVAC/interior electronics, exterior lighting and "ergonomics". Then they look at unique engineering and modifications, fabrication work and "car show stuff" for the remaining 10 points. I saw one entrant who had a power point presentation on his laptop hog 25 minutes of the judges time; others would rattle on and on about stereos, fake roll cages, and all sorts of non-performance stuff I don't care about. Like my general disdain for car shows, this is my least favorite element of Optima, but its a necessary evil and it is't ever going away for this series.

          It is also where they are supposed to weed out the "dedicated race cars" with no interiors, but that doesn't always happen, either. So we had washed Mark's Corvette before this event, but after nearly a day of driving it was dirty so I cleaned up the exterior and interior quickly while waiting in the very long line. I ended up cleaning a few of our other cars in line as well.

          At least we spent some time actually trying to apply the many Optima series + sponsor decals on Saturday morning, and we washed our cars (some did neither), so I guess that helped our scores. The C5 ended up in 5th out of 16 in GTS class, behind only two dedicated race cars, so I guess washing the car helped. Amy's Mustang got 2nd in this category in GT class and our customer James Meeker (supercharged Roush Mustang) got 3rd. Both of those cars have all the street gear and LOTS of mods we've done, so I was pleased with that outcome. But since this is the only competition event that isn't scored by your "ranked" placings, the last placed car in GT class (a gutted race car) still had 17.4 points, whereas the first placed GT car had 20.3 points.

          Moral of the story is don't be afraid to BRING A RACE CAR. This is not meant as a critique of how USCA scores this sub-event, just a warning to potential competitors to help them focus on what matters and ignore what does not. The three driving competitions are scored differently - your actual best lap time gives you a ranking in class, and your rank determines the score (1st = 25, 2nd = 22, 3rd = 20 points, and so on). It becomes obvious that placing well in these 3 driving events in your class is CRUCIAL to winning the overall with all 5 events' scores tallied up.

          The Speed Stop was the other event on Saturday, and my experience in 4 former Optima events probably helped bolster my times, but it still didn't keep me from getting beat by even some Novice AWD drivers in GTS class. This is THE event where AWD really shines, and the top 5 times of this class were EVOs, GTRs and STis.

          Amy got a decent time for GT class but as you can see below, I ended up way down in 7th place for Speed Stop with my 10.584 second time on my 9th and final attempt. Same issues in the autocross fought me here on the C5: grabby clutch made launches difficult and the mismatched pads made for ICE mode stops, so I had to brake at about 8/10ths to avoid rear lock-up and axle tramp.

          After the 6+ hours of driving in the Autocross and Speed Stop events, plus the other hours spent prepping, walking course, or getting judged on Saturday, we were all exhausted. I was pretty disgusted with my driving and the handling in the C5, and was dreading having to drive it 70+ miles around town on the "Road Rally". This is where cars have to prove their worth by following a path on city streets, usually in traffic and on secondary roads with lots of bumps. This C5 was driving me nuts and wouldn't idle, wouldn't start smoothly from a red light, and the exhaust note was maddening.

          I ended up leading 6 other cars from our group at the track to the Rally party, so we only went to the marked checkpoints (beginning and end) on the map and cut out the crazy route they had chosen. Why? Because as we have found out in multiple Optima events in the past, it doesn't matter - they don't have hidden checkpoints and half the field skips the route and just goes to the end. I have complained about this loophole before, but with over half the competitors short cutting the rally and nobody else seeming to care, I quit worrying about it and finally just took toll roads and nice highways all the way to the final checkpoint, at the Pole Position indoor karting facility.

          Our entire group was hungry when we arrived, with most of us skipping lunch due to the long lines in grid and at all three Saturday events. The more competition runs we chose to take meant we could place better, and Amy and I both got some of our best runs at the very end of the day (and in the Speed Stop we both nailed it on our FINAL run). Stopping for lunch was a luxury we couldn't afford. So by the time we made it to the Karting center we were pretty hungry, but it was going to be an hour and forty five minutes before they served dinner, so many folks just checked in for the rally and then left.

          Too bad for them! Several of us burned time buying a "3 race package" that turned into 6 races and we ran the karts all night. The food was Bar-B-Q from Rudy's that was EPIC. With about half the 100 people not there we all got TONS of food, going back for seconds and thirds. The racing action was pretty fun but somebody kept putting me, Jon, and Aaron from DuSold Designs back on the "next up" display, and we kept taking laps. Lots of fun, but I was thoroughly exhausted by day's end after 5 or 6 sessions of karting - on a full stomach, after an exhaustively hot day. It was shorter distance to just drive all the cars home than take them back to TMS and leave them in the NASCAR garages overnight, so we headed for the house. It was 9:30 before we got back home, and Amy and I immediately crashed out while Matteucci was soon snoring in our guest room.

          Speaking of Aaron, he did DAMNED well in his 2015 Mustang PP, which we've used as our test bed for S550 suspension development. The first MCS coilovers, the first Vorshlag camber plates and the first Forgestar CF5 18x11s were fitted and tested on this car, and the results were pretty amazing. This car goes, stops, turns, and rides better than a similarly equipped S197. I'm not kidding - its pretty amazing, and if you didn't know it was a Mustang on the outside, it might fool you into thinking it was a BMW by driving it. Ford nailed it on this one and we got it right on the spring and damping for the suspension.

          Aaron drove well and with this car's bone stock brakes/pads/fluid, stock power (it has an axle-back exhaust), and the other performance mods we've helped develop he placed 3rd overall in GT class, behind the 3 race cars. Initially he was ranked as 4th, but a mistake in calculations put him ahead of one of Ken Thwaits's two Camaro entries in the final tally. Aaron scored 4th in Speed Stop, 7th in Autocross, and 5th in the Hot Lap portion. Dusold Designs has done other mods to this car including a custom grill, tow hook, rear spoiler, custom splitter (not in place for Optima) and other updates.

          So Sunday was the Time Trial portion, and I explained Amy's issues above. She just didn't have confidence in the set-up, with the change to street tires and no aero making the car very different. She put it in the trailer after her big spin. Matteucci took all of 6 laps in one session and the exhaust smoke screen got so bad that he ended the day early. I am stubborn and kept trying to battle my way to a better time with the C5, but only took 14 laps in two track sessions before calling it a day. I've never found a car I couldn't "drive around the problems" in, until the eBay Corvette.

          The clutch was no longer an issue on the road course, unlike in the Speed Stop or Autocross, but the rest of the parts mismatch problems were amplified at the higher speed road course event. The TMS infield isn't a traditional road course and the short course length surprises many with the higher speed corners and treacherous off course potential. There are tire barriers and concrete walls aplenty, but it is what it is - there is no other road course site in Texas that has the room to run the Autocross and Speed Stop simultaneously, this side of COTA ($$$).

          We went out on track in the first session but Danny Popp's GTL classed C6 Z06 entry only made it about 50 feet before something in the transaxle exploded, and the Expert 2 run group got a black flag. He laid down a little oil but the track workers had it cleaned up in about 10 minutes and off we went. Popp also had a set of BFGoodrich Rival-S tires, along with Kyle Tucker, but since those tires wouldn't be available for normal folks for weeks or even months, these two cars were moved to Exhibition Class. That was the right call by USCA and I applaud them for following their rules about excluded tires.

          Danny wasn't the only one who suffered mechanical issues, as the newly built tube framed 67 Camaro of our friends at Dusold Designs also had some teething troubles. Mike was FAST on the autocross course in this lightweight machine but when a control arm pick-up point failed, they had to run back to their shop in Lewisville to build a replacement. They weren't 100% confident in the fix, so after Mike drove the car on the Road Rally they called it a weekend. Didn't want to see this wild but mostly untested creation wadded up on the road course on Sunday.

          My first track session in the C5 was full of traffic but uneventful, other than I was cursing at the car for being such a mess to drive. By session two the track temps were up in the right range, and I knew I needed to lay down a good time NOW. Unfortunately the car just would not stop, turn or corner worth a damn. The non-Z06 C5 gearing is weird, and every corner and straight was right between 3rd and 4th - so it was either making NO power in 4th or revving to the top of the range in 3rd. The brake pad mismatch made the rears lock constantly, sending the rear axle hopping and making it loose. The lack of bump travel in the rear made the rear loose over bumps and in heavily loaded corners. And the peaky cam made the motor come on hard and spin the rear tires.

          The video above shows parts of 6 laps in Session 2, including my fastest on lap 3 - a 42.574 - while passing two cars off line. Traffic was brutal in the morning sessions but because of the spin I had at the start finish line after 6 laps during session 2, I called it a day. I'd already driven a borrowed car harder than I felt comfortable with and I wasn't going to wad it up in a concrete wall. I might have found some tenths in later sessions, but the 39 second laps I did last year in the Mustang were nowhere to be found in the eBay Corvette.

          continued below
          Terry Fair -
          2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
          EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


          • #6
            Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

            continued from above

            I was frustrated with the C5, physically tired, and the car now needed a major bath. So did I. But somehow, even with all my complaining and car troubles, this event was still a TON of fun. All of these frustrations were my own damned fault - for bringing a completely untested car with questionable parts to a televised event before we had a chance to fix the many wrongs done to it. Amy also had a struggle in the Mustang, driving in events she had never done, a course she had never driven, and on tires and an aero set-up she was very unfamiliar with. But she and I had several on camera interviews, we met a lot of cool folks, and got to see a lot of kick ass cars. The Optima/USCA folks took care of everyone and made sure we were having fun.

            Unlike some previous USCA/Optima events, they were very good about posting times up during the event, even had live timing up on Sunday, all of which was a welcome change. Since my driving felt so terrible I had no illusions of placing well in class. Of course there were still some surprises at the results ceremony at the end of Sunday.

            Wow, these cellphone pics have major #potatocam filter going!

            As I mentioned above, Amy's Mustang finished 2nd in the Design and Engineering competition against one of Ken Thwaits' two entries and our customer James Meeker got 3rd - both cars have been featured in this S197 build thread many times (we have Meeker's car in our shop now for more cool updates, which I will share next time).

            As you can see in the results above, James did well at the Hot Lap track event, (using the MCS RR2 doubles + Vorshlag camber plates + Whiteline everything + 18x11 Forgestars) taking 6th place right behind Aaron Sockwell's 2015 GT (which has MCS TT2 shocks and Vorshlag camber plates + 18x11 Forgestars). As I mentioned before, Aaron's 2015 looked good out there and we weren't surprised when he took 5th in the Hot Lap event (somehow a 2 seater 2006 Corvette snuck into the GT class to take 3rd?) and 3rd overall in GT class. Amy, Doug, Jon and even Shannon were all in the hunt on the road course, too.

            Matteucci's 2nd place Autocross and Speed Stop times were good enough to put him into 2nd overall out of 12 in GTS class, fighting against the lightest and fastest cars at this event - in a stock C5 Z06 with a worn out motor (this was the last event he ran in this car before pulling the tired LS6). Ronnie Soliman took 1st in the Autocross, Speed Stop and Hot Lap challenge in his 2006 Evo, which was very light and well built. Those AWD cars are still the overdog cars to watch out for in GTS - and since they combine all the classes for the main OUSCI event, also a threat to win it all in Las Vegas. If I were a betting man that's what I'd pick for the finale after SEMA.

            As bad as it felt, somehow the eBay Corvette earned 3rd overall in GTS class, surrounded again by AWD buggies. This was a complete shock to me, as I felt like my Speed Stop times and Design/Engineering score would keep me off the podium. But hey, I'll take 3rd in this mess of a car. Just going .04 seconds quicker in the Speed Stop would have put me in 2nd place in GTS class, but I was a long way from 1st. That was taken by our friend Todd Earsly in his EVO. Todd made a concentrated effort to focus on Optima events about a year ago, running NASA events in TT1 class on street tires just for the practice, and its really paying off - this GTS class win gets him a spot in the 2015 OUSCI event. Congrats to him!

            The Optima folks worked hard all weekend to keep everything running smoothly, and I'm happy to report that they did a nearly perfect job. Well worth the time and entry fee, so if you see one of their events coming to a road course near you, GO AND ENTER. As Matteucci showed, a stock car on decent tires can still do as well (2nd place with a busted motor) in even the toughest classes, if you can drive well enough. And my entry showed that even a terribly handling mess can still podium sometimes, too. Sure, it helps to have a fully prepped race car in GT class, but so what? Aaron's 2015 Mustang is a real daily driven street car and he took 3rd overall with stock power and just good suspension and wheels/tires (18x11 Forgestar CF5s and 315 Falkens). I'm going to drive Aaron's car soon at ECR event and see how much we improved the stock lap times with the new MCS and Vorshlag parts (I managed a 2:06 in it at ECR when it was bone stock).

            I'm glad our Vorshlag entries that had never done this event before trusted me and entered, and they ALL said they had a blast. We even had several in our group that had done this before (Shannon and Jan) and I'm glad they came back with us again.

            In-Car Video BitchFest + New Light on an Old Class

            The video linked below shares 8 minutes of my first hand impressions of the eBay Corvette after driving it at Optima on Saturday. This was the first day I drove this car, and it was a hot mess. I kind of "go off" on the assembly of parts, the aftermarket, some shock brands, and more. The drone and noise from this Borla system was driving me NUTS in traffic, as was the engine's poor idle, terrible driveability, and other glitches (which we've since fixed completely - see below).

            continued below
            Last edited by Fair!; 05-20-2015, 09:07 AM.
            Terry Fair -
            2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
            EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


            • #7
              Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

              continued from above

              After making that video, I've learned a lot more about this particular car. It was built for a certain class where some of the parts sort of make sense. Some parts on this car aren't as terrible when used in "ideal conditions" - the shocks might work fine on a smooth track and at stock ride height, and the other parts fit this points based letter class in NASA (TTA). So now the choices make more sense to me: using these aftermarket shocks but not upgrading the springs (more points), doing the headers and other exhaust bits (used to be +5), cold air (+1), and the BIG cam upgrade (+6) to get to a target power number. It probably stacked up well against the old C5 Z06 entries that used to rule TTA class. The part selection was also partially budget driven, and that's OK.

              Left: Up through the 2012 season, TTA class was alive and well. Right: By 2013 TTA was dead and TT3 was a whole new ballgame.

              The previous owner raced this car in NASA's TTA class at Hallett from 2010-12, and did fairly well in the car. The lap times (1:24s) were pretty good and he won plenty of contingency tires. TTA was a popular and competitive class that had a LOT of variety, but the C5 Z06 pretty much dominated at the top levels there for years. There are loads of posts about the loss of this class, but by 2012 it was dead and not coming back.

              Since 2013, all C5 Corvettes go straight into TT1/2/3, so "points" mods restrictions are no longer a driving factor in parts selection. Instead of picking selective mods around a class that no longer exists, living with big compromises on the street, and being stuck with stock ride heights, the new owner Mark is going to build it with a bigger budget and NASA TT2 class in mind. So again, sorry if I was too harsh in my video above, and I kind of get it now, but there were still some big compromises to the set-up.

              My "8 minute bitchfest" video also showed some of the driveability items that were above and beyond the problems uncovered during competition at Optima, which included:
              • A glitch which kept the car from running properly or having enough power to exceed about 60 mph with the factory Traction Control turned on (I figured that out the morning we went to TMS, within 5 minutes of driving the car for the first time on the highway)
              • The loud droning of the Borla exhaust was ear splitting at highway speeds
              • The rough tune wouldn't idle or cruise under 1500 rpms; you had to use a lower gear to keep the revs up or it bucked and stumbled, which made the drone even worse
              • The ride quality on the long-ish Konis suffered on the street - any real bumps would bottom the rear shocks, sending the spring rate to infinite
              • The clutch engagement was not smooth and made stop-and-go traffic a hassle. The lack of idle made the engine die when stopped, so you had to drive with 3 feet.

              Long story short, it was a chore to street drive, which was a big ask for only 400 whp. Something wasn't right, and I knew our friends at True Street Motorsports could work their magic and tune out these driveability issues. But first, we needed to so something about this exhaust before they retuned the motor.

              What's Next for the eBay Corvette? UPGRADES!

              So after we finally had a few days to catch up after Optima in March we spoke with Mark and he even come by the shop to talk to us in person about plans. The general consensus was that there were several issues we found at Optima that needed to be rectified, and he had some choices to make regarding the suspension, exhaust, engine tune, and brakes. We also needed to know what color to powder coat the Forgestar CF5 wheels, since we had to rush order the set "raw" to make them in time for Optima.

              So let's get to the fun part of this post - the upgrades! First, here's the former dyno graph from the previous tune done when the cam was added.

              Yes, the image is hard to read but the basic numbers are: 338 whp / 356 wtq before the cam, and 400 whp / 381 wtq after the mega-cam and a tune were added. Big add for the cam, obviously, but it came at a cost of smoothness, idle, and other issues. From what I am told this power level was how the car was purchased by Mark this Spring. Something wonky happened to the tune after this old dyno chart was made, as I've had LG tune our cars in the past and they did a great job. Who knows, but whatever the reason, it ran like crap when Mark received it.

              New Axle-Back Exhaust

              The first item we all agreed needed to change was the exhaust. It was too loud and after looking at it up close, I felt it was also restrictive. The weird routing and tubing sizes looked all wrong to me. Did I mention that the tiny Borla mufflers + full length headers made the car EAR SPLITTINGLY LOUD? Yea, it was unpleasant, and I noted as much in the in-car video - where you can barely hear me describe the issues with the car over the monotonous exhaust DRONE.

              I've built a lot of custom exhaust systems and installed dozens of off-the-shelf performance exhaust systems over the past 28 years of being a hobbyist fabricator/racer, a mechanic at a tuner shop, and then the owner at Vorshlag for the past decade. We have two really good fabricators here (Ryan and Olof) and two engineers that understand flow (Jason and I) and exhaust sound. We are also fanatics for lower weight, higher quality materials, and adding simplicity when possible.

              The Borla axle-back system above isn't great, but it isn't 100% terrible. This C5 already had that installed, plus some nondescript long tube headers, all of which is just rusty enough to be recognized as 409 stainless. The header collectors, cats and mid-pipe section are 2.75" OD but the Borla axle-back section is only 2.5" OD. We know how to measure pipe and have a dozen calipers around the shop, so you're gonna have to trust me on those numbers.

              The routing that the OEM system, this Borla system, and seemingly ALL aftermarket exhaust systems seem to take on a C5 is torturous and needlessly compromised. Its ALL ABOUT THE QUAD CHROME TIPS, yo. There are lots of bends and not a lot of room for a properly sized muffler case. And in the case of exhaust tubing and muffler case, bigger IS better.

              We've done lots of before/after measured sound tests and lots of before/after dyno tests and after years of doing that we have figured out what works and what doesn't matter. When excessive NOISE is a problem we found that a LARGER case muffler of a certain type knocks the sound levels down. DRONE is handled in another way, and PERFORMANCE is all about maintaining a smooth and larger inner diameter and minimizing bends. So we spec'd out the biggest Magnaflow 304 stainless mufflers we could fit in the rear and got those coming, plus a lot of 3" mandrel bent tubing and some real stainless V-band clamp assemblies.

              My new routing idea was fairly simple but not something we'd seen before on a C5 - exit out the side. This let us avoid a pair of 180° bends and a pair of 90° bends as well. This also gave us more ROOM for a bigger muffler case. This isn't revolutionary and since we built this I've had people show me other examples of this routing on C5/C6 Corvettes. Not surprising - its the only routing that makes sense.

              Exhaust leaks are also a pet peeve of mine, and I find any audible leaks unacceptable. There's a half dozen ways to make a multi-piece exhaust system join together, and the "common" ways are the cheaper, most leak prone joint types: slip-fit and ball-and-socket joints are the worst, with bolted flanges with gaskets coming a close second. The proper way we've found, which is the most costly and complicated to install, is a V-band flange connection. Done right, these never leak.

              We also build exhausts to be lighter, and can often save 40-80 pounds over OEM systems. But this car didn't have the stock exhaust, so we didn't weigh the changes. Since I also hate rusty exhaust components, we always stick with 304 stainless steel exclusively. Titanium is a real bear to weld and EXPENSIVE, and the less dense material makes for more noise. So we keep a lot of mandrel bent 2.5" and 3" 304SS tubing around.

              Like all race shops would build it, we piece the systems together from the mandrel bends - slicing, fitting and tacking them together as we go. After tacked we remove the finished assembly and final welding everything on the fab bench. This is the right way to do one-off exhaust systems, but its time consuming and the materials are expensive. Spending 12-20 hours building an exhaust is not unheard of, and at our current shop rate ($105/hour) it can add up. This isn't the right choice for many folks, but when the options are all compromised (like the C5) or its a custom race exhaust where every ounce matters, or you need a quieter set-up than the aftermarket offers - this way works. And we stay pretty dang busy.

              Not shown well is the layers of heat shielding we added on the inside of the rear "fenders" (bumper cover). This includes a composite aluminum/fiberglass mat on the inside surface with DEI gold foil reflective barrier on the top of that, near the muffler case.

              The outside of the body has hand formed (to match the curve of the body) 304SS heat shields shown above, bolted in place with stainless button head M6 bolts. The exhaust system "grows" (front to back and laterally) when it gets hot, so there's a necessary gap around the tail pipes that changes slightly with temperature. If the stainless plates get covered in soot they can be hit lightly with steel wool and be shiny again.

              The new sound (see video below) is a lot more pleasing, still having a bark on the outside but MUCH quieter inside. Oh, and this change along with a re-tune gained 25 whp...

              Sean at True Street dyno tuned it this week and as you can see (above) it now makes 425 whp and 398 wtq. Not spectacular, but its still just a stock 5.7L LS1 with a cam, headers and a cold air. It picked up 25 whp and 23 wtq from the exhaust changes and their conservative "road course" dyno tune (STD corrections). We had them tune it for 91 octane (the best at most Oklahoma gas stations where Mark lines) and for road course use, so this isn't some ragged edge drag race tune, either. In a 3100 pound C5 with 425 whp it goes plenty well, and it would put the car near the limit for NASA TT2 as it sits... (nominally an 8:1 power to weight ratio class, with driver on board).

              Click for video (tested on a closed course in Mexico):

              Why has nobody made a C5 exhaust system "kit" like this? It isn't easy to install nor replicate for an off-the-shelf system that is easy for a DIY installer to put on these cars. There's cutting of the bodywork and the V-band clamps don't have any "slop" to allow for alignment. It was made to fit THIS car. People have already asked me what it would cost to build an axle-back set-up like this and ship it to them, and I said "first, ship me your car". This is a custom exhaust set-up that we have to fit to a given car. Not only are the large diameter tubes tough to fit around things like transaxle, suspension and halfshafts, the exhaust outlets need the heat shielding inside and out.

              Wheels Get Color

              The color Mark went with is a Blood Red powder coat that we had done at a local powder coat shop we've worked with for years. Yes, it was baked under 400°F, yes it is safe, and yes virtually all wheels you can buy are powder coated. Please don't chime in with your internet stories of cracked wheels from powder coating. That was a scare from the 1990s and any decent powder coat shop knows how to coat aluminum wheels without altering the temper. Please don't propagate old internet wives tales, thanks.

              Anyway, the finish came out beautifully and the pop of color really helps this otherwise bland silver Corvette.

              NEXT: Suspension Plans

              We have spec'd some MCS TT2 dampers for the car, which are being built and should arrive soon. We will install these with some other parts we want to make, which I will discuss in the next post. We will be removing the transverse springs in the process and go to coilover springs. Why go to that trouble? Why not spec a custom VBP transverse spring for both ends? Well we almost did that, and had really good results from the 1170 pound VBP (above left) custom front spring on my TTC prepped C4 Corvette.

              After talking with Lex from MCS about this car when he was at our shop recently, he made a simple point: how can you tune the spring rates at the track if you only have $500/each transverse springs? A coilover spring is a whole lot easier to change and a lot cheaper to test several rates with. We can carry a dozen springs to the track and let the clocks show us what works best. Good idea.

              Moving the springs to the shock (coilover) and away from the OEM mounting locations is no trivial matter on this car, though. You are essentially moving all SPRING loads onto places on the chassis and control arms that were designed for DAMPER loads. So things will be altered and beefed up to hold these higher loads. We will share more next time...

              What's Next?

              We have done a lot of events since Optima in our other cars, but the next event scheduled for the C5 is below:
              • May 30th - Five Star Ford @ ECR (HPDE event)

              Originally scheduled for May 9th but was moved due to heavy storms, which gives us time to knock out some work on the C5. This time Mark can make it down to drive the car on proper dampers that don't bottom out after 1/4" of travel. He will never know the joys I had at Optima!

              We're also working on a number of other interesting projects...

              This Week at Vorshlag video for May 8, 2015

              Click above our my latest "This Week at Vorshlag" video, linked here. In that I cover many of the other projects going on in our shop that week, so watch that or check out our Facebook page or Blog to see what we're working on outside of the Mustang world. I write insanely detailed forum build threads for all sorts of other car chassis and types...

              Thanks for reading!
              Last edited by Fair!; 05-20-2015, 09:20 AM.
              Terry Fair -
              2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
              EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


              • #8
                Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                Project Update for June 29th, 2015: We've been working on Mark's C5 Corvette since the Optima event and have made big strides. We have some new products we're testing on this car which are somewhat significant, too. Mark finally got to race this car at an autocross, where I co-drove with him. This was to be a test of the new set-up, but we had some weather issues, which I will detail below. Let's get caught up.

                Unintended Weight Loss

                If you have ever read one of my posts you know I'm a freak for weights... we tend to weigh cars and parts more than other shops, because we know how important weight is in racing. After tires, weight matters most. So let's look at what we started with...

                Left: The weight of Mark's C5 after Round 1 of mods (3114); Right: Weight of a stock C7 Z06 for comparison (3570)

                The 3114 pound weight above was after Round 1 of mods were added - it had almost no fuel, full length headers (lighter than cast iron manifolds), 18x11" Forgestar wheels (the 18x10.5" TSW wheels it started with were even heavier), two composite Sparco race seats, harness bar, and a Borla exhaust. That's not bad, considering what a stock, carbon fiber C7 Z06 Corvette weighs (3570 lbs) - which is about the same as a 4 seat 2011-14 Mustang GT with a giant DOHC V8, stick axle and steel bodywork. Mark came from a 2012 Mustang GT before this car.

                We haven't really done any real weight saving tricks on this C5 in Round 2 of the mods, just component upgrades to make it faster. But we always keep an eye on weights and pick parts that are "weight neutral" or lighter, whenever we can.

                And this picture above is where we are now, with similar fuel levels (almost none), which is 3050 pounds. This is almost exactly what a C5 Z06 weighs (I've weighed one at 3048 lbs, which was stock and low fuel). The Z06 is a lighter car than a coupe from the factory, as it doesn't have the giant glass rear hatch, no removable roof, narrower wheels than this car has, and a titanium exhaust. And while a 64 pound loss might not seem like a big deal, we weren't even trying to remove weight here. The car still has full interior, air conditioning, and we even went with heavier front rotors (Centric 1-piece vs Stoptech 2-piece). So a semi-stripped C5 Coupe could easily get under 2900 pounds or less.

                A Brief Detour To Talk About Time Trial

                This new weight of 3050 + a 200 pound driver with the new 425 whp power number (up from 400) puts power to weight at 7.64:1 (down from 8.4:1 when it got to us), which is a tick better than TT2 territory (8.0:1). This is good - so with a little ballast or bit less power it could get right at limit of the TT2 class, when Mark takes the TT plunge. Sometimes it is tough to fit in one of the three numbered TT classes (TT1/2/3), but this one works out perfectly.

                Does this TT and power-to-weight ratio stuff sound confusing? I talk a bit more about TT classes in this thread on the S197forums. Yes, this is a Mustang forum, but the sub-section (corner carvers) where we read and post there is pretty focused, and we have had some decent tech discussions there. In post #23 there I talk about the pros and cons of autocross vs HPDE vs Time Trial vs W2W racing. Posts #28 and #33 is where I talk a bit more about Time Trial, which Mark is building this C5 for.

                Time Trial rules might seem confusing at first glance by racers from other racing groups or non-racers, but it's really quite simple: measured wheel horsepower and measured weights (with driver) are combined to form a ratio (power to weight). This is the CORE basis for almost all NASA racing (W2W) and TT classes. It works really well - better than "engine displacement to weight" ratios and "turbo modifiers" that the SCCA likes to use (which was dropped in the 1970s by almost every other racing organization on the planet). Let's look at some numbers...

                Relative Ranking of NASA Classes
                TT1 5.50:1
                TT2 8.00:1
                TT3 (stock aero ) 9.00:1
                TT3 (modified aero) 9.4:1
                American Iron 9.0:1 to 9.5:1
                TTB 10.50:1
                Spec Iron 11.75:1
                TTC 12.00:1
                CMC ~12.7:1
                TTD 14.25:1
                TTE 16.50:1
                TTF 19.50:1

                AI, SI and CMC are three popular "pony car" wheel to wheel (W2W) racing classes within NASA, in case you are unfamiliar with those names. There are small power-to-weight modifiers to all of these classes, especially the numbered classes, but these base numbers are pretty much the goal you shoot for. Not all "letter class" TT cars can hit the power to weight max (with the limitations on mods, you are lucky if you can!) but the number class cars can (its just costs money!).

                I ran our TT3 Mustang at 8.8:1, even with the -0.4 "non-stock aero" hit (we picked up an even bigger ratio bonus for running over 3801 pounds, +0.6). We run our TTC Corvette at 11.3:1 with a bonus for only running a 245mm tire (+0.7). And when it comes to the modifiers, "minus equals plus and plus equals minus"... I know, it's wack, just don't ask.

                Suspension Development + Hoosiers

                During the past 7 or so weeks since Optima we have done a bit of development. Lex from MCS stopped by our shop and we discussed shock options for the C5, as well as the two big spring choices - monoleaf vs coilover springs.

                The C5 uses a single transverse mounted monoleaf spring at both the front and rear of the chassis, of course, and the Y-body Corvette chassis has done this for generations. Mark's base C5 Coupe was fitted with the two springs above. There is some associated hardware that goes with mounting the monoleafs, which we removed, shown below.

                We swapped the C5's factory transverse springs for a quartet of 2.25" diameter steel coilover springs from Hyperco, which I have weighed above, top right. So if you add up the monoleaf spring and hardware weights (9.7 + 11.9 + 3.6) that's 25.2 pounds, replaced by 8.6 pounds of coilover springs. Now we didn't weigh the MCS TT2 aluminum bodied monotubes, but they are probably another 4-5 pounds lighter on each corner than the steel bodied Konis that came off (which are already sold). So a good bit of the weight loss in Round 2 came from the suspension changes, the rest was in the exhaust and airbag delete + race steering wheel.

                Coilover springs (left) are more common, cheaper and come in more rate options than monoleaf springs (right), which are built to order

                And yes, we could have used custom built, higher rate monoleaf springs (see above right) instead of coilover springs, and that's what we did on our C4 Corvette for TTC. For the C5 we could have sourced monoleaf springs from the same place as these coilover springs - Hyperco. Why didn't we? Three reasons - cost, availability/options, and time to change springs track side.

                Lex summed it up best: "You can take a dozen coilover springs with you to test at the track - easy to change, cheap to buy, tons of rate and length options. Are you going to buy an equal number of ($500/each) monoleaf springs to test with?" He has a point. At $80-100 each for Hyperco coilover springs, this gives you a lot more flexibility and options to test with, plus they are a lot easier to change track side. Plus they are lighter and don't have any "unintended swaybar effect" like transverse monoleaf springs do.

                After deciding on using coilover springs (which moves the load path of the suspension from the leaf mounts to the shock mounts) we knew we wanted to make some spherical shock mounts for this chassis different than what other companies have made. With these two pieces of info we ordered the MCS TT2 shocks (above) in different lengths and configurations than normal. We definitely didn't want to end up with dampers that were "too long", like the set that came off this car.

                The comparisons above show the front shocks (left) and rear shocks (right), Koni 3000 series vs MCS TT2. The new fronts are shorter and have a little more bump travel. Couple that with our raised height spherical mounts and they had even more travel. The rear was the nightmare with the Koni's, and with ride heights 1/2" lower than stock we were left with only 1/4" of bump travel. That ain't enough. The new MCS body length is slightly shorter, and non-inverted. But the big space savings was moving the adjuster to the top of the shaft instead of the one built into the lower fork. That saves almost 3/4" of an inch in body length alone, which equals more stroke in the bump direction. After you look at the motion ratio of the shock it makes for about 2 inches more bump travel = plenty.

                Here's a close-up of the inverted front MCS monotube double adjustable, which we call the "TT2" shock series (TT1 = single adjustable non-remotes). Like I said, we didn't have the rear shock inverted to save room, but left the fronts inverted (how they normally make them for a C5/C6). That means the rear shocks' 2-stage adjuster knob would be buried inside the "blind hole" that the factory shocks mount into.

                So we cut a big hole above the shock to gain access to the knob. This was a relatively easy fix, and makes for MUCH easier shock adjustments than before with the Konis (jack up car, insert tool, rotate and hope to make both sides the same). Now the knobs can be reached quickly - pop the rear hatch, lift the carpet, and turn the knob. Pull up for compression, push down for rebound, nice positive clicks.

                The C5's rear TT2 shocks us the traditional MCS 2-way knob, shown in the video above - down for Rebound, up for Compression

                The trunk access holes above were made by first removing the rear shocks, looking at the blind hole, then approximating the center of this hole and drilling a 1/8" pilot hole up through the fiberglass rear deck. Once the center of the shock opening was located by this pilot hole, a 2" hole saw (with an 1/8" pilot drill) was used to cut the openings from the top side. We cleaned them up after these pics were taken and temporally stuffed a foam koozie down inside the cavity through this 2" opening, to make a water tight seal around the shock shaft. There is nothing really structural here, and the pilot hole kept the 2" hole saw centered over the blind shock cavity and away from the steel frame rail. We will install a better cover next time the car is at our shop.

                The upper shock mount itself is something we designed and machined in-house, to test on Mark's car. This eliminates a big "double rubber bushing" mount in the upper part of the shock, which becomes more crucial when you move the suspension loads to the shock mounts (which only see "damper loads" in stock form).

                continued below
                Last edited by Fair!; 06-29-2015, 03:32 PM.
                Terry Fair -
                2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                • #9
                  Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                  continued from above

                  We had done the same type of rear upper shock mount on a C5 Corvette many years ago (it never went into production), but this time we refined it by adding easier access to the top knob from the rear hatch area. It's a simple upper mount using our oversized 3/4" spherical bearing with two thru-bolt holes that attach the flange of the assembly into existing threaded factory holes in the rear. Note: the access hole for the upper knob in the rear fiberglass recently became legal for many SCCA folks, see 13.5.F, but converting from leaf to coilover is not legal for Street, Street Prepared or Street Touring classes. It's fine for Street Mod or NASA TT1/2/3, though.

                  The new Vorshlag spherical top mounts are shown at the rear (left) and the front (right) shock locations.

                  We left the factory lower rubber shock bushing on the bottom in place for now, but there are off the shelf conversion kits to make this into a spherical bearing also (maybe we will do this on Round 3 of mods). The front MCS shocks lower bushing is already a spherical, as part of their T-bar lower mount.

                  The front upper shock mount was something a bit more unusual, done differently than the other coilover setups on these cars. Most of the spherical upper shock mounts we've seen for C5/C6 coilover front shocks are really just "eye" upper shocks with an adapter to bolt to the stock pin mount hole. That makes for a tall ding-dong looking device sitting above the shock, and the spherical bearing is way below the factory mounting hole - which eats up a lot of front shock stroke (but gains room for the coilover spring to the upper control arm). Our set-up is unique in that the spherical bearing is slightly above the factory upper shock mounting hole - which gains additional shock stroke. We offset and enlarged the factory upper mounting hole inboard, which is how we gain room for the spring clearance needed relative to the upper control arm. It will make sense when we publish the production pictures + instructions.

                  The face of the spherical bearing mount still has plenty of surface area - more so than the factory rubber bushings did - and can pass the loads into the whole upper shock mounting structure, which is thick multi-layer steel assembly welded to the frame of the chassis. Doing this offset upper hole moves the top of the shock inboard, which gained room for the newly added coilover spring. We also went with 2.25" ID vs larger 60mm ID coilover springs for more clearance to the control arm.

                  Common coilover spring diameter sizes are 1.75", 2", 2.25", 60mm, 2.5", and 70 mm - which are listed from smallest to largest

                  It sounds complicated but was actually quite easy. Again, this atypical spherical mount setup removed a rubber bushing from the suspension load path plus gave us MORE BUMP TRAVEL, both good things. Spherical bearings pivot smoothly and can carry a LOT of impact load, unlike rubber which can bind in pivot and crush in compression.

                  The spring rates we chose were a compromise - like everything on any race car, or any race/street car. Mark has since bought a trailer and decided to make this a more dedicated race car, but... he wants to hang onto some street manners for a while longer - like catalysts, interior and air conditioning - so we had a tough call to make on picking the rates. He was also stepping up from 200 treadwear tires to Hoosier A6 tires, which he told us the week we were installing these coilovers.

                  Jason wanted super stiff and I wanted just moderately stiff, so we argued, calculated, and finally settled on 650 front and 700 rear rates in 2.25" diameter and specific lengths that would fit the confines of the suspension. This is about triple the front spring rate and about double the rear of the OEM transverse springs - we think. You see, there are a couple of ways people measure the spring rates on the transverse factory parts and nobody seems to have real a good, definitive listing of C5 springs' actual "wheel rates" (spring rate at the wheel, with motion ratios and funky spring shapes taken out of the equation). The measurement styles or conflicting spring rate data doesn't really matter - all that we care about is how the springs and dampers perform.

                  Luckily we had a test event scheduled with Mark the next weekend, which we could use to dial in some of the settings, so we worked overtime to get it all together before he came by to load up with his new trailer on Saturday.

                  Making Spherical Bearing Shock Mounts

                  Some folks like watching the step-by-step images we show on social media of new parts as they are developed and built. Here's a few steps of the making of these C5/C6 Corvette upper shock mounts, which happened over the course of 2 days (from design, to a brand new machined part, to on the car and driving).

                  First step is always measurements from a car. The C5 was lifted up on one side and the stock shocks were removed. We test fit the shocks and several springs a few times and saw all of the tight spots. Some measurements and tracings of OEM panels were made, an initial design concept was made for both ends, which Jason and I reviewed together, tweaked, and then he made into a final design in CAD. Then the material was ordered...

                  By the time the two billets of aluminum alloy arrived, the CAM design was programmed and ready for the CNC machine. Specific length slugs were cut on our coolant-fed band saw and loaded into outer jaws in the CNC lathe.

                  The front and rear slugs were machined on one side, then custom soft jaws were installed and machined to grab the "tower" of the rough machined parts. Then the ID was machined to accept the press-fit spherical bearings, with several high tolerance dimensions. This was the first two "ops", completed all on the lathe.

                  The finish machined "rounds" were then ready for the CNC mill, to cut the perimeters of the mounting faces that attach to the chassis. To do this required three fixtures - one to hold the tower shape on op 3, and another two to hold the bases for op 4 on the mill. Lots of programming and setup but very little machine time. We made 8 pieces and only needed 4, and didn't anodize them but left them in raw aluminum - typical of a prototype part. Mark is a tester and knows all of this going into the build.

                  The spherical bearings were test-fit into the rounds to verify the dimensions and fit before they went into the mill, of course. We actually skipped op 4 (just a chamfer on the top edges of the base flange) since they were only for cosmetics and would be covered up once installed. The production pieces will get op 4, of course, along with a red anodized coating.

                  All told about 25 man hours were spent measuring, designing, programming, machining and test fitting these parts, all of which we eat in the name of R&D. Testing should prove the parts work (or need a tweek) and we would have another successful product that we can sell for years to come. We shall see...

                  That's a good visualization of the starting billet and the finished parts. Lots of steps taken to get from round bar to final product, and hopefully you enjoyed the little step-by-step here.

                  Additional Mods

                  Mark has a lot of future plans for this car but wanted a quick release race steering wheel to complete Round 2 of mods complete. We put together an estimate for his requested racing steering wheel and quick release and got he parts coming when he approved the choices, colors and numbers.

                  We suggested the models of the wheel and quick release ultimately chosen, using brands and models we have used in the past. The steering wheel is a MOMO model 88 in 350mm diameter (also available in 320mm) with a black suede covering and flat bottom design. I've used this wheel on four of my own race cars in the past and numerous customer cars. The GM hub adapter is a MOMO piece, which goes to a 70mm diameter 6-bolt circle common to Sparco, MOMO, OMP and other racing steering wheel makers. The quick release hub is from Lifeline, who also makes the Sparco branded part that looks identical. We've used all of these parts before, and sell these to racers all the time. The QR comes in gold and black, and Mark picked gold.

                  We have used a lot of different steering wheel Quick Release hubs over the years. My only advice is this: while there is a big price difference between the circle track QR hubs, Chinese/eBay QR hubs, and the high end hubs like this Lifeline/Sparco unit, there is an even bigger difference in feel and "slop" between the low priced and high priced units. This is another one of these "you get what you pay for" deals, all the way.

                  These parts are often finicky to install and took some special care to get the factory airbag out, remove the OEM steering wheel, fit the MOMO hub adapter, and trim the column surround plastics. The QR hub and MOMO wheel were the easiest bits to install. One thing to remember is that a QR hub always adds depth to the column, pushing the steering wheel about 2" closer to the driver.

                  This worked out perfectly for Mark yet when I drove the car (with a fixed seat placement) it put the wheel a bit close to my chest - but this car isn't built for me, it's built for Mark! And this car, fitted with high side bolster 1-piece racing seats, removing the steering wheel does make it easier to get in and out of. And the new wheel... mmm, it feels so nice. Good stuff.

                  continued below
                  Terry Fair -
                  2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                  EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                  • #10
                    Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                    continued from above

                    Another big change to the set-up was going to real brake pads. I had so many problems with the Hawk HP+ pads on the front at Optima that those thankfully went away forever. We ordered him Carbotech XP20s for the front right now and we are looking at a Big Brake Kit from AP for his next round of mods. Mark rounded up some "gently used" Hoosier A6 tires in the similar sizes as the Rivals I ran before (295/30/18 front, 315/30/18 rear) and we mounted those to the same Forgestar CF5 18x11" wheels.

                    Last but not least, Mark made a move away from his S197 Mustang and that helped fund the "Truck & Trailer Mod". His custom-ordered 18' dovetail steel deck twin axle trailer arrived the day before he had planned on picking up the car - good timing. We had to adjust all sorts of new things - ramps, straps, trailer hitch, load leveling bars, and placement of the car on the trailer - but we got it sorted and loaded the day before the Texas Region SCCA autocross at TMS Bus Lot.

                    Last but not least, Jon made some class numbers and letters for the autocross event. As you can see he ran SSM class, which is more of an "anything goes" class for DOT legal R-compounds. My Sunday customer appointment got pushed at the last minute so I was able to co-drive with Mark at that event, and with 10 runs between us we could dial in the shocks and tire pressures on the whole new set-up. Mother Nature had other plans....

                    Test Event - SCCA Autocross at TMS

                    The event Sunday looked like it could be used for some decent testing of the new set-up of shocks, tires, brake pads and spring rates. Normally I don't like to make this many changes at once, but we knew they would all be beneficial to this car, based on the dismal performance at the Optima event. Who wouldn't take Hoosier A6 tires over worn out 200 treadwear streets? And Real brake pads over budget HP+ pads? And real monotube double adjustable shocks over Konis that bottom out when driving over a penny? And spring rates that firm up the car and remove lots of dive and roll? Here's a couple of pics of the C5 from Optima...

                    Pictures of the C5 cornering at the March Optima event at TMS on street tires and stock springs. Note the front roll on the right pic

                    I am a big proponent of using images of a car in various cornering states to help judge the setup of things like camber, spring rate, ride heights and more. Remember: the pictures above are with the Koni monotube adjustable dampers, stock springs, and pretty dead 200 treadwear tires. LOOK at how much roll there is, yikes.

                    Picture Gallery: (not much there)

                    So here in Texas we've had a LOT of rain this Spring and Summer. Enough that it made national news. But this weekend was scheduled to be clear and warm: 93°F and Sunny - that's a scorcher, so we brought a tire sprayer to deal with tire heat from a 2-driver car using Hoosiers on hot asphalt. This site has smooth sealed asphalt where you can see max lateral grip numbers of only about 1.3g on R-compounds.

                    The course layout was not favorable to bigger cars like this Corvette - this was definitely more of a Miata/transient type course compared to the month before, where we set FTD and Top PAX in our 3600 pound TT3 Mustang (also running in the Street Mod category, below). But hey, you take what you can get when you are testing.

                    I like this event site and we ran our TT3 Mustang here in May (above), where it did very well

                    The sky was overcast when I woke up to leave for TMS, but I thought, "Meh, weatherman said no rain!" so I left my rain gear at home. Along with Mark - me, Brad and Jon from Vorshlag ran in this autocross event. There were 164 entries and 4 run heats, and we ended up having rain in 2 of the 4 heats. Jon, Mark and I got a bit unlucky and worked in heat 2 (where it rained) and ran in heat 4 (where it poured).

                    Our shop manager Brad ran his STX prepped BMW 328is in the "X" class in heat three and had a bit more luck with the weather - this was the magic run heat that was dry, warm and fast. He has waited months on the RE71R (magic 200 TW tire) but they still weren't ready in his size, so he had to run on his old Hankook RS-3 tires, but still managed a respectable 3rd out of 10 in the "Pro class" (PAXed class for National level drivers, if they care to run it) and 8th out of 152 timed drivers in overall PAX. His wife Jen won the PAXed "W" class and also had fast run times, running in heat 2 in the wet/dry. They got dry runs on their 4th and 5th runs, where massive time dropped. I was announcing that heat and the 5th runs were pretty amazing, and virtually everyone got their best run by 2-3 seconds on their 5th.

                    Heat 4 = 1 run then Thunderstorms

                    The weather really screwed up the 4th run heat, though, with one dry run then.... BOOM! Massive thunderstorm with lightning that shut down the event. They refunded 50% of the entry fee for everyone in this heat - it was just hosed.

                    Our order manager Jon ran his green 2006 Mustang GT in the 4th heat with us, taking the CAM-C win on his first and only run. Even with the win he was frustrated, as only having a single dry run ruins your PAX ranking and it's impossible to compare your time to someone in heat 1 or 3 that had five dry runs. It also ruins any testing you had planned.

                    So Mark and I ran in heat 4 as well, and as one of only two 2-driver cars, we were first on the grid. The weather looked bad so I was happy to give Mark the first driver spot, and he took a wild and wooly first run, all in first gear. I wish the camera worked - it was all sideways. I rode along with him (it's allowed here) and we were laughing as he slipped and slid his way around the track. The shock settings were wrong, the tire pressures were too high, but he had fun and we could feel the used R-compound tires start to come in as he scrubbed off some rubber. We lowered the pressures then made some small shock changes, but knew we'd be making more changes soon. It was LOOSE.

                    The "Best" pics I got of the C5 loaded in a corner. Flatter by a significant amount

                    I slotted in next, and realized I was a bit close to the steering wheel. Oh well, no adjustments possible without unbolting the seat, so I just drove it. We had bled the tires down to 30-32 psi, they were nice and warm, and the ground was still dry. It had been about 6 hours since we walked the course, though, and I was having trouble remembering the layout - which worked it's way around and inside itself a bit. Mark rode through with me and we talked a bit during this run...

                    terrible driving in this lone run we got on film in the dry

                    Before you get started with the comments, yes, this run is terrible. I probably should not even show it, as it makes me look like more of a awful driver than I really am. But it was my first and only dry run, so just ignore the over-driving, topping out 1st gear 4 times, and ugly hand use. The car was set WAY loose and a handful to point in the right direction, and the gearing was between 1st and 2nd. By the end of this run you can hear us talking about shifting earlier and doing the whole course in 2nd gear instead of mostly in 1st, like this one. I also tend to calm down a lot when I have a clean time in the books (surprisingly, this run was cone-free).

                    I only show this video because it's the only dry run we got on film. :/ The thunderstorms rolled in after 1st runs and it was all over. I took one run in the rain and was hydroplaning all over the place and fully 16 seconds slower. Then they shut the event down because of nearby lightning strikes.


                    I shouldn't even post the results, because with one run they are meaningless. But I wanted to point out one thing - as bad as that run was, as badly as it was driven, as far from the correct damper set-up it was at - this run time was one of the quickest for first runs, for all drivers in all heats. We were on our way to a good result, and my "butt dyno" felt a 43 second time in the car. Again - it looked bad on video, and it was pretty bad driving, but the car was still pretty fast. That's all that matters here: the car has a lot of potential, and it's not even being built to autocross.

                    After my hilarious slip-n-slide pouring rain run #2, the lightning started and hit close by - across the street - and they sent the corner workers and everyone in grid to find shelter. We camped out in a buddy's truck and waited for the lightning to pass, then I helped pick up the course while Mark loaded his car on the trailer, in the rain. Absolutely not the test we had imagined, but what can you do?

                    OKC SCCA Autocross Testing June 28, 2015

                    Mark took the C5 to an autocross event (yesterday) in Oklahoma where he had 8 runs to dial the car in. Results are posted, but Mark wanted to let me know that he was testing yet took passengers on all of his runs. He had a cone on his fastest run at the starting line, which the side exhaust blew over, LOL! Hey, we were told this was to be a track car, so I can't worry about cone sneezes.

                    If you ignore the "exhaust breeze" cone he had the 4th quickest time of the day, and was still dialing in the car (double adjustable shocks). He is going to come back down July 12th for the Texas Region SCCA autocross event where we will both drive the car again and do some more setup work. Then he has a Hallett test day for Sept 2nd to work on some times on a road course, finally.

                    What's Next?

                    Mark was still happy with the car, as even with only a single dry run he could feel the improvements. The brakes actually worked now that the street Hawk pads were removed. We drove around city streets in the car on Saturday and the ride quality was firm but not unreasonable with the 650F/700R rates, and never bottomed out - even going over some rough railroad crossings. The car cornered flatter and had no noticeable brake dive like before. The sound of the exhaust was both pleasing and much quieter than before. The new engine tune was easier to drive (no more stalling at idle) and the power delivery was much smoother than before.

                    All of the mods from Round 1 (basic repairs + 18x11 wheels and Rivals) and Round 2 (shocks, springs, engine tune, exhaust, Hoosiers) made for dramatic improvements, but more testing is needed to dial in the shocks. Mark could finally take his car back home to Oklahoma and he will be hitting some track events at Hallett (his home track, which is one of my favorites) and some autocrosses in his SCCA region (he has already done one more autocross).

                    We have Round 3 of mods planned with Mark, and they are extensive. These include Safety upgrades (roll bar, HANS, fire bottle, main power kill switch), Brakes (AP brakes front and rear + Ducting), Drivetrain (Gearing, LSD, Accusump, Oil Cooler), and Aero improvements (wing, splitter, more). Once these are tackled it should be a pretty quick TT2 car, but when he gets some lap times at Hallett with the current setup posted I will share them here. The previous owner had some quick 1:24 laps there on Hoosiers with the old Koni/TTA setup, and we shall see if we've made it better or not pretty soon. Since we had my TT3 setup in the 1:21s at Hallett I'm pretty sure we can go faster with a 600 pound lighter C5 Corvette setup for TT2?

                    That's all for this time - Thanks for reading!
                    Last edited by Fair!; 06-29-2015, 03:55 PM.
                    Terry Fair -
                    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                    • #11
                      Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                      Project Update for July 17th, 2015: Short and sweet update this time, after another autocross test event (where we got more than one run) and a slight change in priority of the build, but its pretty cool.

                      Mark's C5 has been driven in anger four times since he bought it - at Optima on street tires, at the June autocross on Hoosiers, another June event in Oklahoma, and now at this July event. The last 3 events were on the new suspension we built and installed and there are some good comparisons I will show below. The last 3 events were also on the same (used to begin with) set of A6 Hoosiers, which began to fall off a cliff and lose performance due to heat cycles and age. It is always tough to test on less than ideal tires, so we didn't make radical changes. I'm still waiting to see this car on a road course - which is what we all agreed that it would be intended for in the first place.

                      Let me just start out with the obvious - summers are HOT here in Texas. We had a bit of a reprieve from our normal super hot June-July-August months with unprecedented rains from early Spring into July this year, but this past weekend was back to "normal" for us - sunny, hot, and humid.

                      It was perfect weather for a Vorshlag pool party the day before this autocross event, which we had at Brad's pool. Started at 3 and I wasn't home until midnight, and we all ate and drank our fill. That 5 am wake up alarm on Sunday for this autocross was brutal. Once again Amy left me to my own devices, and wisely passed on autocrossing at this event herself.

                      Texas Region SCCA Event, Aug 12, 2015

                      I arrived at the Texas Motor Speedway event site at 7:05 am, way too early and way too bright. Felt like garbage but managed to help Mark unload the Corvette off the trailer and walked the course, then slept a bit. This region likes to mix up the run-work order every event, so in June we worked 2nd heat and ran 4th (last), this time we ran 1st and worked 3rd.

                      Mark offered another co-drive so we both entered in Super Street Mod (SSM) class again, which is where the car falls due to the relocation of the spring from the transverse to coilover location. Its not really a SSM car, not hardly, but its just "where it fits" and these events are just being used for some initial testing of the new shocks and springs. By 9 am we had the driver's meeting and then things got underway for Heat 1, when we were set to run.

                      We planned a little better this time and had the "tire sprayer" loaded with water and ready in grid. The temperatures quickly climbed into the mid 90s and track temps were 145°F, as measured with an IR gun, so we needed the water this time. We lined up with the two-driver cars. I ran first, and that first run was a mess. Mark rode with me and we had a lot of wheelspin, but much of that was a dirty course - I was the 4th car to drive on it.

                      We noted throughout the day that while the car would launch pretty hard from the standing start (3000 rpms) we still couldn't use 1st gear much, as the rear tires would start to break loose in a straight line at around 4500 rpms in that gear. So we short-shifted to 2nd at 4500 rpm every run and just used 2nd gear for the entire course. There were three VERY tight 180° turn-arounds and the revs were a bit low coming out of these, but it now has more torque and we didn't want to just shred the rear tires trying to use 1st - unlike the June TMS event at the same site, where we only had one run each before the thunderstorm hit, and both of our runs were terrible.

                      This run group was a bit small and made the event rushed for us. After each run we barely had time to get the tires bled down, switch the numbers, reset the video cameras (one on roof, one mounted inside), spray the tires down (they were overheating badly, especially the left side), and then switch drivers and get belted in and the steering wheel back on. This left very little time to watch other cars, change the suspension settings, etc. In the end we only made a couple of small shock rebound changes, as the car seemed to be handling pretty dang well. The track was cleaning up and also getting hotter, and these outside changing variables kept us from doing any effective shock testing.

                      Back in March at Optima, before the exhaust and tune, the car was "running out of gear" in 1st in the autocross, but 2nd was very sluggish because of the lack of mid-range torque. Looking at the before and after dyno charts, with the new exhaust and updated tune now, there is actually a 50 ft-lb increase in the mid-range, and it was noticeable at this event. Instead of trying to do the 1st-2nd-1st-2nd gear change dance, we could just leave the car in 2nd gear and let the low RPM torque pull us out of the 180° turns without feeling like the engine had no power.

                      What was not working so well were the tire compound and brake booster. The 295/315 A6s Mark got for the June event were used scrubs, and there have been another 60 runs runs put on them since at the June TMS event, the June Oklahoma event with lots of runs, and this July TMS event with two drivers. Not only were the tires extremely HOT (after a run we couldn't touch them for a full second) they were heat cycled out. Dead, kaput, done. I am not a fan of doing testing on used tires, and then there's the fact that autocross competition events don't necessarily make for good tests. But its what we got, so be it.

                      We both noted that the brake booster seemed to run out of assist after each short straight. I have noticed this before in our TT3 Mustang, running at this site back in May, where that car's booster was "running out of vacuum" after two long straights. I had to press so hard on the brake pedal then that I sheared the retaining pin that connected the brake pedal to the booster pushrod on that car. This same thing was happening to the C5 - either there is a vacuum leak in the booster or the big camshaft it has, with lots of overlap, is not producing enough vacuum after ~5 seconds of Wide Open Throttle. We were both overshooting the braking zone on the three 180° turn-arounds on our first two runs. On my third run I calmed down and just braked way early for each stop, which helped me drop two seconds and made for a 48.5 second run. I told Mark to try the same thing and he matched that time on his 4th run (48.6+1). By my 4th run I realized that these tires were blazing hot and weren't gripping like they should, so I slowed down all my inputs even more, which led to a 47.48 second run - the quickest time of the first heat.

                      In-car Video of Terry's (first segment) then Mark's (second segment) best runs of the day.

                      There's some video above that Mark shot with his GoPro of our best runs. Admittedly these runs don't look all that impressive, and at the end of the day the PAX placings weren't very good. Mark had cone trouble on his best run and seemed to be trying to use more steering angle than I was - and the tires just couldn't take it. It felt like we were on very heat-cycled tires, and that's what it boiled down to. I had to baby the throttle and temper the steering inputs or the tires would just run out of slip angle and slide. It felt a little like driving in the rain, to a degree - any abrupt input (brakes, steering, throttle) would over-tax the tires quickly. Driving here in May in my TT3 car on fresh 335/345 Hoosier A7s was a breeze - and had noticeably more grip!

                      But still, even as low as the grip felt and the issue with the brake booster pushing our braking points back in the C5, that 47.4 run was 3rd quickest of the day (out of 134 cars) and the fastest of any "car with fenders". Our best time was only edged out by a tenth of a second in heat 3 by a shifter kart, and again in heat 4, when the surface was cleaner and rubbered in, by an FMod car. Would we have gone quicker in later heats? Mark maybe, but not me - lack of sleep was catching up to me, and I was glad to be done working after heat 3, to head home early!

                      Jon (left) took CAM-C in his 2006 GT - also on MCS TT2s. The S550 (right) is looking quick in FStreet class

                      It was a great event, a fun course, and well run as always. Thanks again to Mark for letting me co-drive and for doing the video, which saved me some time from my normal post-event routine of video editing. It was a fun day, even with the heat and from being pretty tired and dehydrated all day, I was glad to still be able to get some decent laps in. We took 1-2 in SSM against some more heavily prepped Corvettes, so that felt good as well.

                      Before and After Cornering Images

                      Its hard to convey how much better the car handles now than it did before, when it had the Konis and stock springs. One of the easiest ways to improve handling is to reduce roll, dive and heave by increasing spring rate - and when you do that, you can also lower the ride height for a lower center of gravity. Those go together - if you can compensate for shock lengths (like we did with the MCS set) and raise the rates enough to eliminate bottoming, a lower CG is a good trick to improve lateral grip all on its own.

                      Based on a our experience we like to start off with at least least triple the front springs rates and double the rears on a 4 wheel independently suspended car like this one. As grip levels go up even more, so will the need for more spring rate. Of course when you increase spring rates dramatically you always need to improve the dampers to deal with that as well - and high quality monotube adjustables is the way to go. The Koni 3000s are technically monotube adjustables, but both the hassle and "randomness" of their infinitely adjustable valves is what makes them less than ideal, not to mention their excessive length leading to bottoming out the suspension when lowered. So the MCS is a good fit here. We could have used custom high rate transverse springs, and that would have been easier, but again - we like the low cost of coilover springs (Hyperco) vs $500/each custom built high rate transverse springs (Vette Brake Products).

                      OK, no more theory, lets see some data. To me one of the best ways to show the handling improvement, outside of lap times or data logging on a fixed road course (we haven't gotten there yet on this car) is to look at images of the car loaded up in a high-g corner, which we have below.

                      BEFORE: Koni Monotubes, stock springs, 295/315 BFG Rival street tires

                      AFTER: MCS TT2s, Coilover spring upgrade, 295/315 Hoosier A6 R-compound tires

                      As dramatic of a difference as these pictures show, it feels even MORE improved driving the car back to back. Mark didn't get to race the car on the old shocks/springs, but I did - and its a night and day difference. The new setup doesn't have the excessive roll and dive as the old, nor the "infinite spring rate spikes" when the shocks bottomed out, as they did before. This makes the car more precise at turn-in and gives the driver more confidence when pushing the car hard. Sure, the A6s were "compounded out" but it still had some decent grip and a good feel.

                      The improvements are doubly impressive when you consider we have also upped the mechanical grip used with the MCS shocks. Going from (worn out) BFG Rivals to (worn out) Hoosier A6 tires, even in the same size, is a big step up in grip. But the C5 just seems to WANT MOAR GRIP! So we are working toward that next... new tires, and bigger tires.

                      Having run probably 50 or more autocross events at this TMS site over the last 15 years, I feel like I can say with confidence that fresh Hoosiers in these same sizes would have been worth ~2 seconds that day, and on a hot day like this not having 2 drivers running back to back to back would have been a benefit as well. Moving up to wider tires like a 335/345 A7 would be worth even more. I cannot emphasize enough how important tires are in racing!

                      continued below
                      Last edited by Fair!; 07-21-2015, 12:37 PM.
                      Terry Fair -
                      2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                      EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                      • #12
                        Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                        continued from above

                        One more thing to note about this event - the sound readings were great on the C5 and we never blew 100 dB all day, while many others did. I noted some 93-97 dB readings for our two entries (SSM 105 and 5), but nothing out of the ordinary. This site is not sound restricted but many autocross sites are these days, and I was worried the side exhaust might not do well for sound readings. We were topping out 2nd near the sound meter, so it wasn't the best conditions for this car to "blow low" sound, either. I love it when we build an exhaust that can reduce noise levels AND make a +50 ft-pound torque bump in the mid range +25 whp up top.

                        What's Next?

                        So Mark has spoken with me in the last week and is throwing us a bit of a curve ball - it now needs to do well at autocross as well as track. These two motorsports don't exactly share the same requirements, but many of the improvements we had planned can work well in both formats. I have conferred with Jason, Brad and Jon at our shop - all experienced autocrossers, and we have made some suggestions on his new plan.

                        Of course I told Mark my opinions about using "scrub tires" and that if he wanted to get more serious with the car for autocross events it needed fresh tires in wider sizes. If he wants to make it more track worthy, we could likely stick with these tire sizes for a bit and concentrate on aero. Especially for his home track Hallett, which has a few quicker corners (T1, T4, T8-T9) where aero will help. So he had some deciding to do.

                        We had all initially planned on attacking aero upgrades next then attacking wheel/tire width down the road, but we are skipping ahead a step now. Yes, Mark still wants to do the the giant splitter, diffuser, AJ Hartman ducted hood and rear wing - but these will wait until after adding some mechanical grip by way of wider tires first. Why? Well he's going to be doing more autocrosses than road course events right now. Since he's the Regional Executive of the Oklahoma SCCA Region, which does a lot more Solo than Club Racing, he ends up at more autocrosses. So his car is being forced into a more autocross-centric role, at least in the short term.

                        The end goal is still the same - NASA TT2 - but anything that can help that goal PLUS make it quicker in parking lot events will come first. Unfortunately the September Hallett track event Mark had planned got scrubbed due to a work trip that popped up, so his first track test will have to wait a bit, but he does 2-3 autocrosses every month already. So now Mark is scheduled to bring the C5 back to Vorshlag at the end of the summer to allow us to explore ways to fit larger wheels and tires to the C5... namely some 18x13" front and 18x14" rear sized wheels, likely in the model shown below.

                        The new Forgestar M14.2 wheel is a 2-piece design we first reported on at SEMA 2014, and we were told about them before that after talking to the principles at Forgestar about our BMW E46 LSx race car we're building for the 2016 season. These M14.2 wheels are being made in 18x7" to 18x15" widths, in half inch increments, and they are more cost effective than 1-piece monoblock or 3-piece wheels in the wider widths (final pricing has not been announced at this time, but its supposed to be a good bit less than $800/wheel).

                        When it comes to autocross and track handling, the axiom "BIGGER IS BETTER" applies to tire width

                        After years of working my way up in tire sizes on various autocross and road course builds, I'm convinced that nothing performs (via adds mechanical grip) better than TIRE WIDTH and compound. We noted incredible improvements (2-3 seconds per lap, at the same tracks) from the 2013 to 2014 seasons on our TT3 Mustang after switching from 315mm A6 tires (2012-13 events) to 335F/345R Hoosiers (2014-15 events). So we're going to PUT 345s ON ALL THE THINGS!

                        Seriously, this 345/35/18 Hoosier A6/A7 tire is freagin MAGIC. Nothing matters more than tires in racing, and nothing beats this big monster. Its the biggest DOT tire Hoosier makes, and personally I want this tire on the back of everything I drive in autocross or road course events. Mark seems to think it will work on his C5, and I couldn't agree more. He fought for both front and rear grip on the 295F/315R Hoosiers at all three autocross events he has done so far, and going +30mm on the rear and +40mm on the front will very likely make the car faster and easier to drive. Isn't that always the goal?

                        A little bit of this, and little bit of that...

                        How do we get these wheels to fit? Well we'd like a bolt-on composite set of flares (fender overlays) for a C5 that are a cross between the bolt-on aspects of the Liberty-Walk type kits (above left) and the function of the C5R bodywork (above right). We can't just go out and order up some C5R bodywork - it was made to mount to a semi-tube framed car, and is long out of production. So we need to MAKE something. Which is a big task, and we will need outside help here, but we're gonna try. Why? Because nobody makes flares for a C5 to fit this much tire - yet. And the car needs real flares to properly cover the front and top sides of these MASSIVE wheels and tires - to keep the spinning tires out of the airstream.

                        Fitting 315F/335R tires requires a lot of poke (left) and some fender cutting. C5 rear flares don't cover much more tire (right)

                        I've seen numerous C5s try to run wider than the 295F/315R sizes. We found that to be the limits under the stock fenders, which Mark's C5 already has. Stan Whitney's beautiful XPrepared C5 (above left) had 315F/335R tires, but like all C5 racers using these sizes, the tires stick out of the bodywork (poke). To keep from cutting the tires they cut the fenders upwards for bump travel clearance. This trick works for autocross speeds but doesn't work well at road course speeds. Similarly, the "hard parking" flare kits (above right) we've seen offered for the C5 only seem to cover the tops of a marginally wider tire, and barely have any bump travel before they rub. These also leave the front of the spinning tires sticking out in the airstream - which is a drag.

                        Mini-tub conversion on the rear was discussed, but judged to be not worth the effort or class penalty

                        We talked to Mark early on (and mentioned it in my first post) about mini-tubbing the rear, but after researching this further, there are three serious limitations on adding wheel room with minitubs on the C5 chassis. First, there isn't much wheel room to be gained inboard on the rear (1" of width), as the rear suspension control arms quickly become a limiting factor. Second, it is a lot of work/expense for very little gain in width. The most you can do with a mini-tub job on a C5 is a 19x12" wheel (18" wheel barrel hits the control arms sooner) so it is not much help. Third, modifying the inner fender/tub isn't legal in many racing classes, or incurs a "non-production chassis" power-to-weight ratio penalty, like in TT1/2/3 (see below).

                        7.3.2 - Restrictions and Limitations for Production Vehicles

                        A) Other than the listed exceptions, every Production vehicle must retain its unmodified:
                        1) OEM frame rails/rear frame cross beam, and/or Unibody, and Sub-frames/
                        suspension cross-members (in their OEM locations)
                        2) Strut/shock towers
                        3) Inner/inboard side of the fender wells (any non-horizontal aspect)
                        4) Rocker panels
                        5) Transmission tunnel
                        6) Floor pan
                        7) Windshield frame location

                        7.4.2 Modification Factors (TT1/TT2/TT3 only)

                        The “Modification Factor” listed after each item below is added or subtracted from the actual measured Wt/Hp ratio to determine the “Adjusted Wt./Hp Ratio” that determines vehicle legality in each TT class.
                        • Non-Production Vehicle: TT1 & TT2 = -0.4
                        • TT3 = -0.7
                        The rule listed above is straight from the 2015 NASA TT ruleset. It might not seem like much, but a -0.4 ratio penalty is rough. Consider that as a TT2 car this C5 will have 7.9:1 pounds per hp ratio limit (with a +0.1 bonus for running 3300-3399 pounds comp weight), but the minitubs would knock you back to 8.4:1. On a ~3300 pound car like this (with driver) that -0.4 penalty equates to 20 whp you would have to give up or 165 pounds of additional ballast.

                        I'm used to making wide body flares in steel, and if you've read any of my forum posts since about 2006 you know this. But fiberglass... ? Man, I hate working with composites. Fiberglass is a messy, stinky, nasty material to work with. And when you cut or sand this stuff it makes a dusty, itchy mess that gets everywhere, including in your lungs and the pores of your skin. But... its the only thing that makes sense on a car with a body entirely made of fiberglass. Yea, yea, yea, your buddy is good with carbon fiber, which is bitchin' and all, but not practical for low volume production or one-off flares. I've worked with CF and its an expensive, complicated, messy, stinky, nasty material to work with!

                        First we need to get the wider wheels/tires on the car (left) and clearanced. Then (right) flares are built around them... "Easy!"

                        Once we have some sort of foam/wood/fiberglass bucks built up on the car, we will work with a mold maker friend of mine to hopefully make short production runs of something we can replicate - hopefully. I'll post up any news here, so don't ask me a thousand times what they will cost or when they will be ready for sale. I have no idea, but if something goes into production it won't be introduced in secret. Read this thread and you will now the latest on whether this worked for production or if we just made the one set for Mark.

                        That's all for this time - thanks for tuning in!
                        Terry Fair -
                        2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                        EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                        • #13
                          Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                          Project Update for October 12th, 2015: Well some things happened to the C5 that changed the priorities for a few upgrades. The intended budget for flares and wheels was instead spent doing some repairs to Mark's C5 in august, but luckily he was wise enough to let us work in some upgrades while the car was apart at our shop.

                          A co-driver took Mark's C5 for a ride through the weeds, way off course at an Autocross over the Summer. While the off-course excursion was underway the only thing within 100 feet that could damage the car was hit - a big, steel propane valve.

                          I don't have good "Before" images, as our crew stripped the front end right after the car arrived, to assess the damage underneath. The front bumper cover was destroyed, as you might imagine from these structural pics, but the frame, subframes, wheels, exhaust, and the rest of the bodywork were unscathed.

                          This propane valve was poking up out of the ground about 6 inches and dug a hole through the front end, then tore up a number of things under the chassis. The bumper cover was shredded, the tubular front bumper support structure was twisted like a pretzel, the radiator and condenser were smashed, one of the control arms was pushed back, and a header primary was crushed.

                          This car was lucky - it could have been a lot worse. The car sort of V'd into the valve, then when it dug into the front end it pushed up and "jumped" up over it, so nothing behind the header collector took any further damage. The valve was rock solid, so the car could have sustained more structural damage to the floor and rear suspension if it hadn't have "jumped up".

                          I don't know much more about the incident, so don't ask. Yes, it is very rare for a car to sustain damage at an autocross - this is still the safest form of motorsport I know of this side of video games. It was a new site they were using for the first time and his co-driver just... "lost it". Going fast. Luckily Mark had invested in a truck and trailer, so he was able to winch it up on the trailer and drag it down to us, without having to call a flat bed wrecker.

                          Crash Repairs = Perfect Time for Carbon Upgrade!??

                          With the front bumper cover and structure wiped out I thought it might be a good time to go ahead with the previous plans of a splitter, ducted hood, and carbon front end.

                          One possible way to "fix" the damage was this upgrade, but it was pricy

                          I tried hard to get Mark to upgrade the front to C5 carbon fiber nose + splitter + ducted hood made by AJ Hartman (see above). Looks so good, but there's a lot of fabrication required to make it all bolt up.

                          We're a dealer for AJ's parts and love his carbon work, so I worked up a good quote for Mark... but it was still pretty pricey. Part of the estimate was a big "unknown" - the custom structure needed (see above) to support the splitter, heat exchangers, and bumper cover.

                          Plus to work with AJ's ducted hood the intake manifold has to be flipped 180° and the throttle body is then fed from the cowl, which entails more modifications and unknowns. Try as we could, I just couldn't give him a solid enough estimate he could live with. But hey, I tried!

                          Front End Repairs and Upgraded Radiator

                          The C5 stayed at our shop while we assessed the damaged, ordered parts, did repairs, then did some nice little upgrades.

                          Finding the bumper cover and front radiator/skid plate structure was pretty easy. The new bumper cover is a good bit lighter than the OEM bits (typical with Taiwanese replacement parts) and Olof took the badges off the stock piece and transferred them over.

                          The new square tubular structure that holds the radiator and bumper in place is a pretty lightweight piece, but it comes in bare steel. The old one was rusty and we didn't want that to happen to this one, so we cleaned it with Scotch-Brite and wax & grease remover, then painted it with 3 coats of semi-flat black enamel paint.

                          As that went in the car, so did a massive all-aluminum DeWitt C5 radiator. This thing is 2x as big as the core on the OEM unit, and didn't have plastic end tanks glued in place. That's good for both cooling and reliability upgrades.

                          A new A/C condenser was attached to the radiator, which took a little modification since the new rad was so much thicker. But it still fit within the confines of the two original equipment heat exchangers and the unit slid back in place nicely.

                          With the old (destroyed) radiator out of the way we noted some crusty, nasty funk inside, as well as the water pump inlet and outlet. This seemed like something worth showing to Mark, so the picture below was sent and followed up with a phone call...

                          Apparently even the fancy GM anti-freeze isn't perfect, and 13 years of use had led to a lot of deposits in the cooling system. We could flush out the engine pretty well, and it was getting a new radiator, but we felt a water pump + thermostat + t-stat housing replacement were a good idea.

                          Mark agreed and since the front of the car and radiator were both out of the way this was an easy water pump swap, adding very little time (a whopping 30 minutes).

                          There were little wiring repairs, riv-nuts that had to be reinstalled in the frame (see below), and lots of little "fiddly bits" to fix, but it was straightforward.

                          The front end repair and radiator install only took about 5 hours of labor, which isn't bad considering how much damage there was.

                          The lower air dam was replaced with OEM plastics, as the old ones were worn from time and torn up even more in the incident. Luckily the aluminum front subframe wasn't damaged, so it was left untouched. We're not a body shop so the front nose was left in bare ABS black when it left, but Mark said he had a guy that would wrap the car soon.

                          Two of the tie rods were looser than before, and all four were original, so we suggested replacing the outer tie rods at all four corners. This was actually very easy as we had the suspension apart for bushings, shown below.

                          continued below
                          Last edited by Fair!; 10-12-2015, 06:40 PM.
                          Terry Fair -
                          2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                          EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                          • #14
                            Re: Vorshlag Build Thread - Mark C's 2002 C5 Corvette Track Rat

                            continued from above

                            Polyurethane Bushing Upgrade

                            This next round of work was no fun to do, but it will make an improvement in performance. Since the front right lower control arm had shifted in the incident it needed new bushings, at a minimum. And with over a decade of time and use the rubber suspension bushings were looking a little ragged, so it was time for poly.

                            Replacing rubber suspension bushings (especially hydraulic filled ones) with firmer durometer polyurethane material is an old racers trick, at least for cars that cannot use Delrin or metal bushings. This C5 is one of those "tweener" cars... it is a dedicated race car that is trailered to events, but... it might someday end up in a racing class that forbids metal bushings. And metal bushings have a higher wear rate and are always noisier. Properly greased, poly bushings can be silent yet remove the majority of rubber bushing deflection under cornering and braking loads.

                            Using heat (propane torch), pressure (30 ton press) and elbow grease the OEM rubber bushings were removed from all 8 control arms. These things are bonded to the aluminum so the heat is necessary to get them to come out.

                            Getting the new poly bushings in place takes pressure (press) and patience. This is tedious work and gobbled up hours of time. There is one important step next that many people ignore...

                            Grease zerks were added to every bushing location. This involves drilling the control arm and tapping it for the grease zerk. With 1-piece poly bushings you also need to drill through the bushing, so grease can get on the inside, next to the sleeve it rotates on. Then line up the holes (2-piece split bushings usually have a gap in the middle that grease can pass through). This ensures that if the bushing grease pushes out over time (it will) it can be re-lubed to quiet that joint. A dry polyurethane suspension bushing not only makes noise it adds "stiction" to each joint.

                            A little forethought must be used to map out where the grease zerks should go - don't just go drilling holes willy-nilly. Think about how the control arm will sit at ride height, full bump and full droop. You don't want the zerk getting bound up on the subframe and getting snapped off. You also tend to grease these with a car on the lift at full droop, so leave yourself access room for greasing them in that suspension position.

                            All told this was over 10 hours of work, but likely something that will never have to be done again. Again, with proper lubrication these should give at least a decade of silent use.

                            An example of why this is necessary: We had a Miata that came in our shop about 2 years ago that we installed poly bushings on. We had started adding grease zerks (to the front control arms points) but the customer didn't want to pay for that, so we stopped at only the front bushings. I should have insisted - two years later one of the rear bushings was worn out because it was dry (had not been lubricated). These poly bushings should get a little squirt of grease every 6 months or so, sooner if they make any squeaks. Its back at our shop now getting grease zerks added to the other joints today, after replacing the bad bushing.

                            Spherical Lower Rear Shock Mounts

                            The only rubber left in the suspension at this point was the rubber lower shock mount for the rear. It was a big honkin bushing, and that will deflect under bump loads - delaying the damper reaction as well as the spring.

                            We looked for a solution and found one from Pfadt, which is owned by someone new lately. I'm not a big fan of their shocks or other parts, but they seemed to have one of the only spherical conversions for this shock mount, so we went with it.

                            This was relatively easy to swap out since the rear lower control arms were out of the car getting poly bushings at the pivot points on the subframe. This Corvette is now rubber bushing free in the suspension.

                            Steering Column Lock Defeat

                            Like all factory built cars, the C5 Corvette has a theft deterrent in the steering column where if the key is removed or turned to the off position, the steering wheel "locks". This makes it harder for a thief to drive your car if he "hot wires" it.

                            But when you are racing and, say... you lose the brakes.... drivers are taught to kill the motor, and let engine braking (an engine is just an air pump, once you remove fuel and spark) help slow the car down. But if you do that with a stock steering column, and go past "off" on the switch, you just lost the ability to steer. After you lost the brakes. Not a good situation to be in.

                            Normally whenever we are prepping a race car there is just a mechanical "pin" that locks into the steering column, which we can drill out or remove. But GM had to get fancy and make a motorized doo-dad that did the same task. This is driven by a Body Control Module, but this system is a well known failure point - leaving you unable to steer your car after started-up and limiting speed to 2 mph while driving with the locked column. And of course, after this many years, this car's steering interlock system started to flake out. When it would do this, the steering wheel would lock after you started the car, and you couldn't steer. So.... yea, that needed to go.

                            We could have ripped apart the column to find the interlock motor but that causes other problems. So instead we ordered the LMC5 Module shown above, which is a kit to electronically disable the electro-mechanical steering interlock system.

                            It has to be wired in under the dash but Brad managed to knock this out in 1.75 hours, while standing on his head. Now the GM system is removed and the steering wheel can always be turned. A better theft deterrent is removing the wheel altogether...

                            Header Repair + Rear Exhaust Hangers

                            The header repair was pretty basic, but it was tricky to do with the header attached to the car. Ryan made a template of the mashed in bits then cut out the smashed section...

                            Getting that cut out cleanly while still in the car was tricky. He then took the template and transferred it to some stainless 1.75" tubing. The round patch was then TIG welded over the hole in the primary tube for a repair.

                            A rear exhaust hanger was broken in the "off" so both rear hangers were also replaced.

                            A Move To 315 Rival-S Tires

                            Last but not least Mark wanted to try a set of 315/30/18 BFGoodrich Rival-S tires. Why go from A6 Hoosiers to 200 treadwear Rivals? Well there's reason to believe that the CAM category in SCCA Solo might grow next year to include CAM-SS. Not to mention these tires give him the opportunity to race with both USCA/Optima and Goodguys, which are on his list. Mark has already run the C5 at Goodguys, since he picked it up.

                            Currently the CLASSIC AMERICAN MUSCLE (CAM) category encompasses 3 classes, but the C4-C7 Corvettes are excluded. You can see the basic CAM rules here. There's talk (and we've written letters) to include the newer Corvettes in their own CAM class called "CAM-SS" for 2016. If so then Mark wanted to have a tested setup ready to go on Day 1.

                            Olof removed the dead Hoosiers from the 18x11" Forgestars and mounted up the 315 Rival-S tires. Brad cleaned the wheels with some pressure then some SONAX wheel cleaner to get the rest of the brake dust off. That stuff is magic... it turns color when it reacts with the metal in brake dust.

                            Speaking of brake dust, the reason there was so much was because the pads were gone. The old HP+ pads on the left and new XP12 Carbotechs on the right. Olof swapped in these new pads all around.

                            All Fixed - Ready To Race

                            After all of this work was wrapped up, the Corvette was ready for autocross action once again. We cleaned up the whole car for Mark - since he never washes it!

                            One little freebie we threw in this time was the new decals. Since Mark's co-driver paid for the front end damage repairs, so we figured the least we could do was make him a sponsor decal.

                            More Autocrosses + What's Next?

                            One of the first event's Mark did after picking the car up was a local autocross, which he used to get the car dialed in on the Rival-S setup. He then entered the All American Sunday (AAS) autocross class as the October Goodguys event at Texas Motor Speedway

                            He was leading all day and into the last runs, but then Aaron Sockwell snuck past him on their final runs to take first place, with Mark in 2nd. Tough loss, as 1st pays out a free set of tires and all sorts of swag at Goodguys. Aaron drive's a 2015 Mustang GT that we also used for suspension development on the S550 chassis. It also sports red 18x11" CF5 Forgestars, 315 tires, MCS TT2 doubles, and Vorshlag camber plates. Aaron also ran this course on Friday-Saturday in a customer's 67 Mustang, so he had a little more experience on that course.

                            He has been running the car in more events since and having a ball.

                            At this point I have no idea what Mark will want to change next, if anything. The suspension feels great now and shouldn't need much from here on out. The motor makes great power but it could always make more, of course - just costs money! The gearing is a bit mismatched for autocross speeds, so a rear gear ratio change might be in the cards.

                            Of course I'd still like to see the move to BIG wheels and tires, but cost of the flares and the labor are up there. Who knows, this might be this car's final form for awhile. And that's not a bad thing.

                            Last edited by Fair!; 10-12-2015, 05:29 PM.
                            Terry Fair -
                            2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                            EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev


                            • #15
                              Re: Vorshlag C5 Corvette Development Thread

                              Project Update for September 3rd, 2016: Mark has been having a blast with his C5 Corvette over the past 10 months, other than a transmission issue we fixed . There's now a newly rebuilt C5 Z06 transmission in and the improved gearing was a huge improvement over the base C5 transaxle. Shifter has been upgraded to an MGW from a Hurst, and more motorsport appropriate AP brakes were installed up front - their lightweight 4 piston Sprint kit with 2-piece rotors.

                              Mark and co-driver Chase have driven the car numerous times this season in autocrosses from Dallas to OKC. The car has bounced back and forth from SSM (on Hoosiers) to CAM-S (on BFG Rival-S tires), on the 18x11" Forgestars with 315mm tire sizes. I've autocrossed in this car a number of times, too, so let's get caught up on this C5 Development thread.


                              The gearing for 1st and 2nd gear were not working well for autocross use in Mark's "Coupe" 6-speed car. Remember - his C5 is not a C5 Z06, which has different transmission gearing for 1st thru 3rd gears (and 5th and 6th as well). Let's dig into some tech here to clear things up.

                              There were actually 3 different transmissions (technically - "transaxles") and 3 different final driver ratios used in the C5 generation Corvettes (1997-2004). There are also some extra names for some of these transmissions - mash-ups of two RPO codes - as well as redundant RPO codes (2 codes for the same thing) to make it all extra confusing. Below are the actual GM RPO codes for the C5 drivetrain options, based on this this link and interweb research. I'm not even going to touch on the C6 stuff, which is similar but different.

                              RPO option codes for C5 Corvette transmissions ans final drive ratios:
                              • MM6 Transmission, Manual 6-Speed, 85 mm, 2.66 1st, 0.50 6th, O/D
                              • M12 Transmission, Manual 6-Speed, 85 mm, 2.97 1st, 0.57 6th, O/D
                              • M30 Transmission, Automatic 4-Speed, 4L60-E, Electronic
                              • GU2 Axle, Rear, 2.73 Ratio
                              • GU6 Axle, Rear, 3.42 Ratio
                              • G90 Axle, Rear, 3.15 Ratio

                              These are codes that confuse people, because they are completely redundant
                              • G92 Axle, Rear, Performance Ratio (this just means the car has an "optional ratio")
                              • MN6 Merchandised Transmission, Manual 6-Speed Provisions (means it has a 6 speed manual)
                              • MX0 Merchandised Transmission, Automatic O/D Provisions (means it has an automatic)

                              The Borg Warner "T56" (that one is not an RPO code, but instead a model name from BW) 6-speed M12 code transmission was the only gearbox offered in the C5 Z06 and the MM6 code was the other 6-speed manual offering in the Coupe and Convertible. The M30 (also known as the 4L60E, and shorthanded as "A4" by some internet folks) automatic 4-speed transmission came with a tall 2.73 (GU2) final drive ratio but there was an optional (G92) 'performance' ratio of 3.15 (G90) that could be ordered on that car. All 6 speed manuals in all C5 Corvettes came fitted with a 3.42 (GU6) final drive ratio. The differential housing (on the back of the transaxle, which holds the final drive ring and pinion + limited slip differential) for the 3.15 and 3.42 ratios are larger than the base model automatic's 2.73 housing.

                              There were other changes with the C6 generations, which all had more powerful engines (LS2 = 400 hp, LS3 = 430 hp, LS7 = 505 hp) than the equivalent models of C5 generation (LS1 = 350 hp, LS6 = 385 then 405 hp). Mark's C5 has a slightly modified 5.7L LS1 engine (camshaft + headers + cold air) and makes 425 whp on a chassis dyno, so that's roughly 475 hp at the crank.

                              The video above
                              has sound clips from this C5... sounds meaner than "slightly modified"

                              Here are the two main 6-speed transmission gear ratios, by RPO model:

                              M12 (Z06) 6-speed gear ratios:
                              First: 2.97
                              Second: 2.07
                              Third: 1.43
                              Fourth: 1.00
                              Fifth: 0.84
                              Sixth: 0.56
                              Reverse: 3.28
                              Final drive ratio: 3.42

                              MM6 (base C5 Coupe and Convertible) 6-speed gear ratios:
                              First: 2.66
                              Second: 1.78
                              Third: 1.30
                              Fourth: 1.00
                              Fifth: 0.74
                              Sixth: 0.50
                              Reverse: 2.90
                              Final drive ratio: 3.42

                              The Z06 Corvette's M12 has lower gears (higher numeric ratio) than the MM6 for gears 1-3. Fourth is the same for both. 5th is lower and more usable in the M12. 6th gear is never used for performance driving - it is the mega-driver highway gas mileage gear, which is only slightly different between these two models.

                              Calculations for speed in each gear, 3.42 final drive, M12 vs MM6

                              The goal in all autocross cars is to optimize speeds in 2nd gear, which is the gear used almost exclusively for the majority of the time spent on most courses. The goal is to achieve a terminal speed of most courses usually between 70-75 mph. Racers will run speed-in-gear calculations (as shown above) with their max engine RPM (7000 in this case), tire height (25.5" tall for 315/30/18 tires), final drive ratio (3.42:1) and the gear ratios in each gear for the transmission. As you can see 2nd gear on the MM6 transmission in Mark's car goes all the way to 87 mph! That's faster than the top speed in virtually any SCCA autocross you will ever see. With the Z06's M12 6-speed swapped in, however, 2nd gear goes to 75 mph. This is damn near optimal for 90% of the autocrosses you will ever see. With a 75mph terminal speed in 2nd gear that means the Corvette will be also geared better on more courses for all speeds under 75mph.

                              But changing the transmission in a C5 Corvette is an expensive job - both the parts and the labor (8-11 hours is often quoted just for the R&R). Finding a known good used C5 Z06 "M12" transmission is also difficult, as these are no longer sold new. You would normally have to source a correct used M12 transmission (money), then have it refreshed (more money), then have it swapped (time and money).

                              Option 1 to "fix 2nd gear speeds" change would be to alter the final drive ratio by changing the ring and pinion in the differential. The common change is to a 4.10 ratio, which will lower 2nd gear speeds closer to the speed range we want. Changing the final gear ratio in the differential is much more expensive to do in a C5 than in solid axle RWD cars like a Camaro or Mustang, where you can buy the ring and pinion set for under $200 and have them installed professionally for $350-500 in labor/small parts. On a C5 Corvette, which has a rear transaxle, you end up paying around $2000-2500 for parts and labor to change the final drive ratio. That's just how it goes, no short cuts or cheap parts here.

                              Option 2 is to change the transaxle out completely, from the MN6 to M12 geared 6-speed. This will always cost more, because it takes more labor (9+ hours) and the parts cost more ($3000-3500 for a core M12 trans + a rebuild is common). But in the case of Mark's car, where 4th gear synchros and mean gear cluster were worn badly, this was the right way to go.

                              SWAPPING TO THE C5 Z06 (M12) TRANSAXLE - TWICE

                              Since Mark knew his Corvette's original MM6 had a blown 4th gear and needed to be fully rebuilt, he took the plunge and went for the M12 transmission swap. This was a better route than going for a rear gear change + upgraded differential + MM6 transmission rebuild.

                              Mark found a great deal on an M12 transmission that "had just been rebuilt" from a race team, made the deal, and had it shipped to our shop. He paid a good bit for it, due to the freshness of the rebuild, but it seemed like it was overall going to be cheaper than what we could have done for an M12 core + a proper rebuild + the trans swap combined.

                              We normally have a policy of not allowing customers to bring us used parts to install. Why? Because if a customer supplied a part, we install it, and the parts turned out to be junk, we aren't liable for the re-work to fix it. Even though we didn't supply the parts, that situation always makes the customer upset. We have learned this the hard way - and that it is the right policy for shops to stick by. Mark has been a great customer, so I bent the rules this one time... let him bring us parts, but I warned him if the parts weren't any good the labor to fix it "was what it was". He understood and took the risk, with the benefit of that he might save up to $1000.

                              To remove the C5 transaxle you have to drop the rear subframe as a unit along with the "torque tube". This is the aluminum tubing section that houses the driveshaft inside and bolts to the bellhousing and transaxle. The clutch is up front like a normal front engine car but the transmission and diff housing (transaxle) are mounted out back.

                              Of course nothing went according to plan, on the car we originally coined the "eBay Corvette". One more janky piece of previous mechanic work from the past bit us. There are several bolts that normally thread into the bellhousing which hold the torque tube in place. Three of these were stripped - it took almost no effort, but these three would just spin and spin. But they wouldn't come out...??

                              We realized later that instead of threading into the housing, the holes had been stripped out and nuts had been super glued to the inside. That temporarily held the nuts on the inside of the bellhousing, just long enough so they could be snugged up and impacted tight. And while you technically can tighten a bolt and hidden nut this way - once - the bolt won't come apart without cutting the heads off. The glue had long since stripped out, so when the bolts were touched to loosen them, they just spun and spun. Cutting the bolt heads off took some time, as did the installation of three Keenserts to fix the stripped threads in the bellhousing. This is a type of heli-coil but with 4 teeth that you use a special tool to set into place. Super strong, fix it once, and forget it.

                              Once those 3 bolt heads were cut off the remaining hardware was removed and the transaxle + torque tube could be dropped out. Then it went on the bench and we started transferring the torque tube and rear mounted differential unit to the "new" M12 unit.

                              This was another strange "fix" we ran into when disconnecting the shift linkage. There was a bolt that had been tack welded to the shift rod coming out of the transmission. This rod had all sorts of hacked up marks on it from a previous mechanics work with what appeared to be a chain saw. We cut the welds loose, cleaned up and welded the deep cuts on the shift rod, and replaced the hardware with new parts.

                              Since both the M12 and MM6 used the same differential housing and 3.42 final gear we just unbolted the back diff section from the old (MM6) trans and bolted it to the "new" (M12) trans.

                              continued below
                              Last edited by Fair!; 09-03-2016, 04:41 PM.
                              Terry Fair -
                              2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
                              EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev