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Unread 07-21-2015, 10:59 AM
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Default 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!
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Unread 10-12-2015, 05:17 PM
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Default 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 at 06:40 PM.
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Unread 10-12-2015, 05:18 PM
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Default 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 at 05:29 PM.
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Default 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.


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 at 04:41 PM.
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Default Re: Vorshlag C5 Corvette Development Thread

continued from above

Once the differential housing was attached to the transmission (above), then the torque tube could be reinstalled (below).

Below are pictures of the hydraulic throw out bearing and the Keensert installation tool, for this thread diameter and pitch.

With everything bolted together once again it was time to raise the transaxle + torque tube assembly back into the car.

That all went back in place and the rear subframe then went in below that. The exhaust went on and we were ready to drive it.

One other thing that happened while the Corvette was here that week were new front ball joints. The old ones were cooked (likely from brake heat + age). Toe was realigned of course. We changed the rears as well.

Mark had also upgraded the front brakes to the AP 4-piston fixed motorsport calipers and 2-piece AP rotors, from their "sprint" kit, shown above. The rear brakes stayed intact.

Test drove the car and the synchros seemed even worse in this "rebuilt" M12 than the worn out MM6 trans that we removed. Mark came into town and drove it and he noted the same thing - it was a hot mess. So out came the M12 trans and I took it our local Tremec specialist (Joe D) for an inspection. Joe opened up the trans and called - it was a mess inside. It needed everything from synchros to gears, shift forks to bearings, seals and blocker rings. Took some time to source all of the parts, but $2300 later it was rebuilt and ready to go back in. At least this time there weren't stripped threads and bolt heads that needed to be cut off - it went in painlessly and quickly.

The race team that sold him this M12 owned up to some of the unreported damage, and I think Mark worked out some partial refund? The extra R&R work - since the transaxle had to come out again, get rebuilt, and be reinstalled - ended up as twice the normal install labor, plus the extra price of a rebuild on top of that. The C5 was also sitting for about 8 weeks while the trans was rebuilt then reinstalled, which sucked for Mark (no racing) and for my shop (storing the car for 2 months). Moral of the story is - always assume any used parts you buy need to be completely rebuilt!

With the fully rebuilt M12 transaxle now in place, the Corvette was back racing in March. The new 1st and 2nd gear setup worked SO much better now, with 2nd gear speeds that are much more usable. The only time 3rd gear is needed are on GIANT autocross courses, which we sometimes see at Mineral Wells Airpark events - like the 2016 CAM Texas event and the 2016 Texas ProSolo (see below). At every other normal course, however, 2nd gear is the only gear needed and slower speed corners have more usable torque on corner exit.


In May 2016, Mark wanted to improve the shifting of his car further so he ordered an MGW shifter from us. MGW shifters are made in the USA and the owners are super cool folks who road race regularly.

Mark and his co-driver Chase managed to install this shifter in the C5 and ever since it shifts even better than before.

With the long shift knob and the short throw shifter combined, the total shift throws are very manageable, the effort is low, and the "reach" for the knob from the steering wheel is a lot closer. Its a perfect shifter setup for this car.


In an unusual move for me, I have raced in 5 SCCA autocrosses this year, all in various CAM class cars. I ran Scottish Joe's 5th Gen Camaro twice and Mark's C5 Corvette 3 times so far. I fought GM's ABS system "ICE MODE" programming at all 5 events, and it frustrated me a great deal. How isn't this more of a thing? Why does GM suck at programming their ABS schemes? The Ford ABS is light years better than the Corvette or Camaro ABS. When I brake hard the ABS on these cars often "freaks out" and just stops... stopping. Pedal turns to a brick and I blow through a gate or cone wall.

2016 was the year of Cones and ABS Issues for me?

I'm also pretty rusty when it comes to autocrossing, probably since I haven't done much of this in the past 4 years, but its coming back to me, bit by bit. Its tough for me to jump around in other people's cars, and my "cone count" is higher than it has been in years. I'm either ICE MODE'ing the brakes or clipping the cone bases (like above), so don't take my results and videos as an accurate portrayal of how these cars are handling - a faster driver can always make these cars look better.


Event pic and video gallery: https://vorshlag.smugmug.com/Racing-...CAM-Challenge/

Vorshlag was an event sponsor for this CAM Challenge event as well as the Texas ProSolo, so since I was gonna be there to cook for people anyway... I found co-drives at both events in some of our testers' cars.

Three Vorshlag test vehicles all running in the Texas CAM Challenge

We were still testing a new setup on Joe's car and at the CAM only event, when it had fresh 305mm Hankook tires and new 19x11" wheels, where it still had a bit of a push.

You can see the understeer we are fighting in the video above. One more event after a front spring change and more camber and we could have this one really dialed in.

3800 pounds of fun and came in 2nd out of 19 CAM-C cars (with our shop manager Brad coming in 8th in the same car) at the 2016 Texas CAM Challenge, and damned if I didn't run the time to win in the brackets, but coned it. I lost in the Saturday runs by 1.4 seconds to an old friend and Vorshlag tester Brian Matteucci in his white 2015 GT, shown above.

Mark and co-driver Chase were mired a good ways back in the CAM-S class, driving the C5 and fighting with "dead" tires. They were about 4 seconds slower than what we ran in the Camaro, which shouldn't be the case in an 800 pound lighter car. All year BFGoodrich kept running out of 315mm and 335mm Rival-S tires, and this was one of those periods where the C5 was shod with "compounded out" tires (I think they had 200+ runs on them at this point).

No major changes were made to the Corvette before the next event, other than fresh 315mm Rival-S tires were mounted.


Event pic and video gallery: https://vorshlag.smugmug.com/Racing-...Texas-ProSolo/

I have co-driven Mark's Corvette three times this summer: At the Texas ProSolo in June, at an SCCA event at Lone Star Park in July, and at another regional in August. We are loaded up and heading to the 2016 SCCA Solo Nationals right now, too. I will give a brief overview of these 3 events so far in 2016.

2016 Texas ProSolo: https://vorshlag.smugmug.com/Racing-...Texas-ProSolo/

This was a fun event where I got to run the C5 in the merged CAM class for the Pro. Once again I was chasing Vorshlag tester Brian Matteucci's 2015 Mustang GT. Brian runs a Forgestar 18x11" CF5 wheel, 315/30/18 Rival-S, Vorshlag camber plates, GT350R springs, Eibach swaybars and a Torsen T2R diff with 3.31 gears - all of which we supplied to him. Brian is brutally fast in this S550.

I kept fighting with the ABS system's "ICE MODE" and my best right side run had a cone after when the brakes simply stopped working in one corner. Sure, I can "brake less" and not engage this glaring fault in the ABS programming, but damn it you shouldn't have to drive around these issues in all GM cars. Why can so many other car makers program their ABS systems to work with a wider range of grip and brake pad compounds without issue??

At this ProSolo Brian and I were paired up in the final 4 runs, and while I edged him by .3 sec in time overall for both sides, he beat me by .3 sec in the paxed times. The Corvette was really loose on corner exit at this event, and with the hectic nature of ProSolos (you run 2 left and 2 right side runs back to back) there isn't time (nor are you allowed) to change shock settings between runs.

Come to find out later, the rear shocks were set at an incorrect amount of compression, and we didn't catch it until after my runs were over. No wonder why it wouldn't launch well or put power down on corner exit. My runs were filled with lots of little driving mistakes, and I didn't have a single 4 run grouping without a major ABS brake system failure and subsequent "cone binge". I could not reprogram my brain to brake more gently than I am used to in autocross situations. The S197 Mustang ABS system ruined me, I guess? At least a Vorshlag tester took the win and the top 5 out of 7 in CAM were Vorshlag test cars once again.

continued below
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Default Re: Vorshlag C5 Corvette Development Thread

continued from below

SCCA at Lone Star Park, July 30, 2016

Event pic and video gallery: https://vorshlag.smugmug.com/Racing-...-Park-July-30/

At this SCCA regional event Mark's Corvette had 3 drivers - Mark and Chase drove it in CAM-S while I jumped up to "X" class to run it in a different heat. And heat was the key word - it was 97°F during my runs and I forgot to bring my cooler - which led to heat exhaustion that day pretty badly (2 other people at this event went to the hospital that day, from the same effects). It hit me so hard that day that it has crept back and got me another 3 times this summer. I'm really trying to stay ahead of it by drinking lots of water and Gatorade type drinks, but heat is really killing me this year.

You can't see it as much in the in-car video below, but I was fighting the ABS system in all of the big braking zones once again. This run the ABS completely goes bonkers on me and I blew 30 feet off line. The GM ABS is really starting to spook me - I just cannot use the brakes as hard as I can in a Ford, BMW or Subaru. Frustrating.

The handling was much improved with proper rear compression valving set this time, and my raw time was pretty good on my 3rd run, but I clipped a damned cone again - just ran over the base. By my 4th and 5th runs my hands were shaking badly, I slowed down, and I knew I was in trouble with dehydration. That run heat took almost 2 hours and there was nowhere to hide from the relentless sun. By days end it was 104°F and I was close to throwing up. After the Corvette loaded in my trailer and I sat in the truck for 30 minutes with the AC on full blast, trying to regain control of my brain, with a pounding migraine from the heat exhaustion. I somehow got home, then drank a lot of water and passed out by 5 pm and slept for 14 hours. I felt terrible the next day, my whole body hurt. This was a bad day.

My results in the "X" class were marred by my 3rd run cone (4th and 5th runs are thrown out in "X"), so I was somewhere near the bottom of the class. Mark and Chase ran in CAM-S a later heat but were about a second behind my best clean run. The rear tires were really giving up the ghost that day. They have been racing the car every other week all summer on this set, ever since the ProSolo, and did a huge number of runs on the rear tires. After this event we all decided the rear's needed to get bigger, so talked about an 18x12" rear wheel and 335mm tire for the remainder of the season.

SCCA at TMS Bus Lot, August 28th, 2016

Event pic and video gallery: https://vorshlag.smugmug.com/Racing-...t-TMS-Bus-Lot/

This was last weekend's event, but the day before I was at Motorsport Ranch running baseline track times in my wife's 2013 FR-S. I got overheated and was feeling sick Saturday afternoon. On Sunday at the autocross I was already starting "behind" on my hydration, and heat exhaustion kicked my butt again on Sunday. This was getting ridiculous.

I made a point to bring a stocked cooler with waters and Gatorade drinks and kept one in my hand all day, drinking non stop, but the previous day's damage was just too much to un-do. It wasn't even that hot, only about 90°F when I left at 2 pm, but I was feeling it while driving. I hit a record 6 cones over 5 runs in Mark's car that day, fought ICE MODE on every run, and had arguably my worst drive of the year. Right before Nationals, yay...

This layout was what I call a "busy little Miata Course" - as are all of the courses at Texas Region events - but that's what we had to navigate in this car. Mark was ahead of me all day, and I just couldn't seem to get ahead enough on the courses or stay off the cones. I am not even showing my in-car video, its just awful. Mark, however, drove very well and put .425 seconds on me that day and pax'd top 20.

We both felt the recent changes (see below) of new swaybars and wider 18x12" wheels/335mm tires made a big improvement out back. Mark's run above shows the Corvette doing so much better in corner exit than ever before.

Running on fresh 315F/335R Rival-S tires, 18x11/12" wheels, MCS TT2 coilovers, Eibach bars, August 2016

The MCS TT2 coilovers and new swaybars have improved the turn-in massively, and the roll/lean was visibly lower in head-on shots. Compared to the first time I drove the car on "good" tires, at the Optima event in 2014, its a night and day difference. That (below) was on 295/315 Rivals and Koni shocks with stock springs and bars. The new setup (above) has wider and sticker 315/35 Rival-S tires, yet radically less roll/dive/lean.

Running on 18x11" wheels, Koni dampers, stock springs and shocks, and used 295F/315 Rival tires, April 2014

So Mark was feeling good when we loaded up the Corvette that day, but I felt like crap again. And this was our last test event before heading to the 2016 SCCA Solo Nationals. I agreed to this months ago, but now I'm heading back to Lincoln for the first time in 4 years on a "low" for the season. I've gotta get my head in the game and stay hydrated next week in Nebraska. CAM-S is no joke at the National level. If anyone reading this sees me in Lincoln without a bottle of liquid in my hand, tell me to get some water!


After the July event and before the August autocross we brought the car back to Vorshlag for some updates. After the August event we installed fresh front tires on the C5, in preparation for the Solo Nationals. I will quickly show that here.

The aftermarket swaybar choices for the C5 aren't all that great, but we had supplied Mark's dad's C6 Corvette with an Eibach setup earlier this year. They were adjustable at both ends of the car and nicely built. So Mark wanted a set of Eibach bars for his C5. We ordered the C5 versions (no good pictures exist) and they showed up... non-adjustable. Oh well, they are tubular and larger in diameter, and Donnie installed them here with grease zerks and fitted the bushings to the bars so they can rotate (endlinks removed) with "pinkie effort". That's my rule on swaybars - no bind in the body mount bushings is allowed. Drilled, zerked, fitted, and greased every time.

When I won a single BFG tire for my 2nd place finish at the ProSolo driving Mark's car I donated the winnings to Mark - it was his car, after all. We requested the Rival-S in a 335/30/18 size and rounded up two more 335s after they had run out of stock this summer (thanks for the hookup, whoever you were), which arrived the same day as the wider rear wheels.

Earlier this year we saw some long lead times on custom Forgestar wheels, but this summer the wait times have shrunk as they invest in higher stocking levels of wheel blanks. A pair of 18x12" F14 wheels were custom spec'd rush ordered in "raw" finish (that can save you as much as 3-4 weeks) and mounted with the new 335s out back.

The 18x12's have way more "poke" that I would ever spec for anyone, but Mark finally broke down and said he's commit to flared fenders - at all 4 corners - after Nationals. So we really ordered these 18x12" wheels for the front, but will use them on the rear for Nationals. Forgestar confirmed to me on the phone yesterday that they finally have 18x13" wheel tooling and these wider blanks should be arriving in October time frame. So the rears on this car will go to either 18x13" F14 or 18x14" M14 2-piece Forgestars. The car might switch autocross classes, too.

The 315/30/18 Rival-S has been on backorder for many weeks as well, so we did some searching and Mark bought this set of 4 wheels and 4 new 315s mounted but never raced. Two of these became the "National set" of fronts.

Running race compound brake pads makes the wheels dusty in a short time. One autocross and the red wheels look black (above). One of the things I'm always giving Mark grief about is how dirty he lets the Corvette get. He doesn't care - clean doesn't mean fast - but I keep reminding him that the giant "VORSHLAG" decal on the side means that I do care. So every time it is in my shop we seem to be cleaning it...

We found a trick to cleaning metallic brake dust off of powder coated wheels years ago - a German chemical cleaner called "Sonax wheel cleaner", which I have mentioned here before. We have been ordering this stuff online and it is a bit pricey. Now there's a cheaper USA-made alternative called Code RED, which you can find at Pep Boys stores for about half the price per ounce. It uses the same chemical process that reacts to the iron particles in brake dust, which changes color from green to red once the process is finished. This must be washed off before it dries, and sometimes it takes two coats and some scrubbing, but its the best stuff I've ever seen for cleaning brake material off of wheels.

Another pet peeve of mine with this car for the past year has been the unpainted front bumper cover. We replaced this when his previous co-driver had a big "off" and tore up the nose, but Mark wouldn't let me get it painted then. This time, as a condition of my co-drive, I insisted.

Our friends at Heritage Collision Center in Sherman, Texas did a fine job and painted the nose and licensed plate cover back in body color. They had to do a bit of bodywork, as the unpainted nose took a lot of bug hits over the last year which damaged the surface. It looks as good as new now.

Jon here at Vorshlag made some fresh "class/number panel" decals for the side and they classed up the car a bit from the hand cut tape decals (oiy!).


We worked on some other things this summer, some of which are not finished, and I will talk about them after we readdress them after Nationals. For now we have the C5 as "ready as it can be" and loaded in the trailer. I leave for Nebraska tomorrow, picking up Mark along the way. I have no idea how we will do at Nationals, but I haven't been in 4 years and it will be fun to be there racing, win or lose.

Vorshlag is also sponsoring the "Nationals Winner" jackets for all of the "supplemental" classes: CAM-C, CAM-T, CAM-S, and STP / STPL. These are all classes I feel are too important to ignore, and we have pushed the SCCA hard for two of these classes to be created (namely CAM-S and STP). I will do a write-up after Nationals and talk about the other systems we have been working on, as well as talk about the new autocross classing plans Mark has for this C5 in 2017.


Last edited by Fair!; 09-03-2016 at 04:52 PM.
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Default Re: Vorshlag C5 Corvette Development Thread

Project Update for September 11, 2016: After returning from the 2016 Solo Nationals I had a pile of work to catch up on, so I worked all weekend and then sat down to do my post-event write-up. It will be brief as we haven't done any work on the car since returning, and Mark still has to decide what class to run next year: CAM-S or SSM. I don't have anything poignant to say about 9/11, even after being at Ground Zero a handful of weeks after this terrible event (it was still burning) - other than to say "I will never forget". I also lost a family member while I was at Nationals, and two others from the CAM/Optima community passed away during the same week, so that's been a bit rough.

There were some potential rules updates in CAM that were discussed and I will go over what was proposed at the Town Hall Meeting during Nationals. I drove pretty poorly and finished just outside the trophies, 7th out of 21 in CAM-S. Pretty disappointed in that, but the C5 ran solid and "coulda been a contender" with a better driver. Even with all of that we both still had a LOT of fun at Nationals this past week and I'm glad I went. It has been 4 years since I last attended - too long - but the fresh outlook of CAM is what brought me back.

Photo and Video gallery: https://vorshlag.smugmug.com/Racing-...olo-Nationals/

I usually take hundreds of pictures during my trips to Solo Nationals, but I had a bunch of stuff on my mind and just didn't take a ton this time. My wife Amy is usually with us and also snaps pics, but she didn't have a car to race this year and stayed home to work. The photo gallery above only has a little over 100 pics, mostly of the CAM cars, but also a few oddities we noticed during our 5 days in Lincoln.


Most people don't live in Lincoln, Nebraska, so the vast majority of the 1350+ competitors at this year's Solo Nationals had to travel to this very centrally located event site, where the SCCA has held Nationals for the last half dozen years. For some folks (on the coasts) the trip spans days of driving or a transport service and a flight, but we brought Mark's Corvette up inside my trailer with our Ford F350 towing flawlessly. This truck is by far the nicest vehicle I own and has more horsepower (400) than any of my current race cars, which is kinda sad.

From Vorshlag's Plano, Texas location, the trip to Lincoln was about 640 miles, which should take about 9-1/2 hours with no stops. I had to stop in Edmond, Oklahoma, to pick up Mark. Luckily that was almost directly on the way North to Nebraska. I left my house at 6 am Sunday hoping to get to the event site, unload the Corvette, and unhook the trailer before dark.

We grabbed some breakfast in Oklahoma and kept driving north. Once we got into Kansas we drove for hours across this vista of corn and windmills, then we had a blowout on the trailer. GRR, I hate trailer tires, and replaced all 4 of them after I had 4 blowouts on the way too and from Miller for NASA Nationals in 2013.

I know why this happened. Where I park my trailer on my property two tires are shielded from the sun by trees, but the other two (right side) get baked. I was suspicious of these two dry rotted tires before we left, but after replacing two front truck tires my "trailer budget" was pretty slim, so this blowout wasn't a huge surprise. We stopped within seconds of the tread cap coming off so it didn't do any damage. We installed one of two brand new mounted spares in a handful of minutes, and were back underway. #500psi

Not 10 minutes later I got popped by a cop doing 63 in a 50 zone. I was really being careful not to speed, because I hate getting speeding tickets in these flyover states, some of which are known to fund their municipalities with speed traps. The Kansas and Nebraska highways have lots of changing speed zones, going from 70 mph to 55 mph and back again, quickly and seemingly at random - there's nothing out here but fields of corn!

The rest of the trip was uneventful, other than pulling into a Kansas fuel station to be greeted by the bare ass of CP competitor Jeff Stroh mooning us as we pulled up to the truck stop pumps, LOL! We saw lots of fellow autocrossers traveling to Nebraska, of course. We arrived on site in Lincoln by about 5 pm Sunday and managed to unhook, unload, and get the Corvette through tech in less than 2 minutes (no line yet!). We also checked in at registration before the lines got too long on Monday. We parked 3 trailers from Texas racers in a circle to shield us from the unrelenting wind and inevitable rain.


This was Mark's first Solo Nationals but I had been many times and understood the schedule. Monday is always when the Town Hall Meeting is held, which is one of the only times the members get to speak with the BOD, SEB and Advisory Committee (AC) folks face to face. I am not a huge fan of the way that rules get made, and have sent hundreds of letters to the SEB over the years, so I show up at these when I can.

After a politically motivated shit storm following the 2012 Solo Nationals, I had walked away from the SCCA for the past 4 years, vowing to never build a car around SCCA Solo rules again. I've stuck to that plan, which has made my life easier. I do miss the challenge of Solo and as you have seen here in this thread, have dipped my toes back into the SCCA Solo scene in the past year. It was the brave new world of CAM that brought me back, so I wanted to go to the Town Hall to hear what was on the horizon for this category - to make sure that this set of classes stays as "un-SCCA" as possible.

After some introductions and opening remarks by the SEB, they open the microphone to racers that want to bring up questions. Several sad pleas from SSR racers (this is a "throw-back" Super Stock class that still runs Hoosiers, that is quietly dying), and some talk about a potential revival of Street Prepared category with some "too little, too late" rules updates (this once popular category is also dying), we broke up into groups where the AC's met with members to talk about rules and trends at tables spread across the tent area.

The wind was howling and felt like the tent would blow away at any minute, so we had to almost yell to be heard from 5 feet away (see video above). The "rules czar" of CAM, Raleigh Boreen, met with the interested CAM racers. We had a good discussion about the 3 existing classes. As many of you know, CAM is a very new category for SCCA, isn't (and may never be) "Nationally recognized", and the somewhat unlimited nature of the rules falls well outside of SCCA norms. That's why I like it - this isn't some 5 decade old category with old and busted rules, entrenched racers resistant to change, and is almost completely devoid of the politics that wrecks many classes over time. There is no "committee", which is probably why CAM has only one page of rules for 3 classes.

Still, there were some concerns voiced by a few racers. "Money in racing" is always brought up, and the "have nots" always want an equalizer. Luckily that was largely ignored in this "builders class", so we moved onto other details. The existing rule for "+150 pound penalty for Lexan front windshields" was discussed, argued, yet most folks missed the point entirely (double pane safety glass windshields are safer, and side and rear Lexan windows are not a safety issue). Raleigh reigned that in and we moved on.

So CAM is pretty simple: domestic front engine/RWD cars, some wheelbase limits, 200 treadwear tires, limited aero, and a minimum weight are all that the rules really care about in CAM. But the minimum weight in CAM-S (2350 lbs) is way lower than CAM-C (3200) and CAM-T (3000). CAM-C (newer with ABS) and CAM-T (older w/o ABS) are for 4 seat cars, and CAM-S is for the 2 seat cars with a shorter allowable wheelbase and ABS is allowed. CAM-S was supposed to be for real and kit car Cobras, and they can weigh about 2350 pounds in stock form.

We lobbied to have the C4/C5/C6 Corvettes and Vipers added to the CAM category last year - initially asking for a 4th class called "CAM-SS" tailor made for these modern 2-seat domestic sports cars with a 2800 or 2900 minimum weight. We had hoped to keep this separate from CAM-S and the uber-light Cobras (and other CAM-S builds people can dream up, like tube framed ultra lights based loosely on some domestic car built in the last 115 years) and keep the min weight attainable without a tube frame build.

At this town hall, Mark and I brought up the 650 pound penalty that is added to C4/C5/C6 Corvettes and Vipers in CAM-S. So we plead the case for moving these cars out of CAM-S into a new class called CAM-SS, and leaving the older 2 seat Corvettes (C3s are popular), Cobras, and lightweight custom builds in CAM-S. Or at the least dropping the 3000 pound min weight for them in CMA-S. Not wanting to rock the boat, we just wanted to follow the original plan for CAM: Classes separated by "old and new" + "4 seat and 2 seat" guidelines. Some CAM-S racers didn't want this, yet they don't want to race against "superior chassis with ABS" like the C5/C6 Corvettes. Some even suggested moving the C3 Corvette into CAM-T, which most CAM-T racers vehemently argued against.

There were the "no rules!" folks, who oppose any changes, and a few weird arguments like "weight doesn't matter", arguing that the 2350 pound Cobras were somehow at a disadvantage because they were 650 pounds lighter - which I openly scoffed at. A handful of racers in CAM agreed that the 4th class, CAM-SS, would be best to move these modern ABS equipped cars away from the existing CAM-S classic cars. Hopefully this is the only change that comes of this Town Hall meeting, as the rest of the ideas just went in circles and didn't fix anything. Closing the 650 pound penalty in CAM-S still allows for the "crazy" builds but lets the more abundant C4/C5/C6/C7 Corvettes a place to race on a level playing field. Ultimately it is up to Raleigh, and he said he was aiming to have the 2017 CAM rules posted early - by November 1st or Thanksgiving at the latest - to give racers time to adjust for any tweaks to this new class.

So we will see what becomes of that and Mark will decide where to take the C5 next soon after. SSM allows some big aero and of course Hoosiers. CAM-S has street tires, no aero, but seems more fun. And there are "damned rotaries" in CAM!

The practice course is running most days during Nationals held on a separate part of the site far away from the grid and main course areas. The Nebraska Region SCCA runs the practice and it sells out weeks or even months ahead of Nationals. Mark thought ahead and bought a 4 run pass for us to use to get familiar with the concrete surface and maybe make some small changes to the car.

We ran this on Monday before the Town Hall, with our 4 runs slotted from 2-3 pm. The wind was powerful and blew over the timers every couple of minutes, so in the 5 chances we had to check out the course we got no times on 4 of those. I got a somewhat lackluster time on my "sighting run", the first shot at the course either of us took, on cold tires. Instead of sticking around another hour trying to get re-runs on the 4 "no time" runs, we just packed it in and "saved the tires". I've made drastic changes based on runs from previous Nationals Practice courses and it always bit me in the ass. The car felt a little pushy, and we adjusted tire pressures UP from our local asphalt courses to this grippy concrete, but left the car alone otherwise.

The rest of Monday was spent sitting around waiting for the course to be open for walk. We roamed around and got stopped by dozens of people, even ran into Brett Madson, who was my pick to win CAM-C (and he did, by a good margin).

We walked the West course only, which was what we would be driving first on Tuesday. All of us scratched our heads at the unusual way that the course was marked. It was dominated by 3 cone clusters and cone walls, which I felt would lead to a lot of lost DNFs and cones (it did). On our first walk through we would find the #500psi cone, which was one that got pounded the most on this course.

Bret's SN95 Mustang is pretty much a maxed out CAM-C build. It has a 2-valve 4.6L V8 that makes 380 whp (???). It is built light and has hundreds of pounds of lead in the rear frame rails, so that helps the front-to-rear bias greatly. It has a built T45, he runs 335 mm Rival S tires at all 4 corners, and uses modern Watts Link and decent spring rates. Nothing exotic, easily attainable, just one of the first folks to really build for CAM-C. He also drove his ass off and won the class by nearly a second.

We ran across a lot of funny stuff in the paddock, like the fully furnished tent with hot tub in one area. The "Taco Truck on Every Corner" golf cart. Lots of wild SM cars with giant tires - a friend asked me to take pictures of the Subarus in SM, so you will see lots of 315mm and 335mm shod Subies in the gallery.

The BRZ below left had a neat GoPro video camera mounted to a tow hook at the front, which I thought was a novel idea. This was one of nearly 150 of the "86 twins" that filled STX and CS classes. CS had 86 cars and STX had 72 entries, both with a very heavy BRZ/FR-S contingent. Giant freakin classes!

After a long day of activities on Monday we headed to the hotel to check in. Mark had a room at a fancy Marriott downtown he got on hotel points, which was really nice. This was the first time I had stayed in a hotel in "The Haymarket", which is the downtown high end hotel, food and bar district. It is always where we end up going to eat during Nationals, and it actually makes sense to stay there if you are going to eat there - other than the F350 barely fit inside the parking garage.

continued below

Last edited by Fair!; 09-12-2016 at 04:05 PM.
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Default Re: Vorshlag C5 Corvette Development Thread

continued from above

We ate well in the Haymarket district restaurants with a different group of racer friends each night: Buzzard Billy's had decent Cajun food, BurgerFi had a great burger and onion rings, and we had some good grub at Lazlo's.

I didn't get much sleep that week, however, as a certain somebody who's room I shared snored like an unmuffled rotary at full revs. I stayed up and watched the F1 race, surfed the interwebs, and listened to music on my phone until there was a break in the sound, then I would doze off and try to start my side of the snoring battle. With 1-2 hours of sleep each night it began to catch up to me, but I managed to drive "about like I usually do" through mild sleep deprivation.


Tuesday morning bright and early was already hot - damn hot - and breezy. Sunday, Monday and Tuesday were all sunny days with ambient temps in the 95°F range each day, so I made sure to drink plenty of water and consumed most of a case of Powerade that week. Always with a drink in hand, trying to stay out of the sun, and slathered in SPF50 sun screen when I needed to walk course or stand in grid. I managed NOT to get heat exhaustion or sunburned all week, which was a major accomplishment for me.

It was super busy that morning, and I was assigned course work during heat one for FP, GS and STX Ladies. The West Course kept us hopping and the 1.5 hours flew by quickly. Then we waited for one heat in our paddock before another course walk between heats 1-2 and we gridded up in heat 2.

Day 1 run 3, Terry driving terribly

I didn't bring my good camera with us to grid on Tuesday so all of these pics are from Wednesday on East course. The in-car video above is my 3rd and final run from this West course, which kicked my ass. It was hard to see and I got caught out with mistakes on every run. Mark and I both had trouble here, as did many others - even the designer for the West Course coned every run on his own course.

I stayed off the cones, but probably too far off. I was driving too conservatively, always seeming to get on throttle too late, turning in too early and getting "behind" on the cones in every section. This made for some slow times, which seems to be par for the course lately for how I've been driving in Mark's Corvette. Which is a shame, because the car was working beautifully! I managed to stay out of "Ice Mode" on the ABS, which seems to be less prevalent in this car on concrete than on asphalt. It is still there, but just harder to achieve.

There was a 3rd gear shift necessary in the final section before the finish that I struggled with. In my 2nd run I was going for 3rd and hit a bump, which popped my visor halfway down, and the bottom edge went right across my vision. I was blind for about 3 seconds, so I reached up and popped the visor down so I could see, then when I looked up again I was 30 feet offline and about to plow down some cones. My first run was crap and this nearly aborted run matched that time, so I went into run 3 with nothing but junk. It was more of a "safety" run than anything, trying to be clean and salvage something for day 2.

Mark had issues on every run and his 1st attempt ended up being his fastest. He started off well but just never got faster, which always hurts. I think we were both caught off guard at the higher grip levels available on Rival-S tires on concrete, as neither of us had any experience with this tire on this type of surface. Both the OKC and Texas Region SCCA events are all held on asphalt - we lost our last 2 concrete lots in Dallas 2 years ago - and it shows. We kept trying to push ourselves to go faster, but the tires always seemed to have more in it.

Serious autocrossers will travel to Lincoln to run the Spring Nationals and even some of their regional events before Nationals, and we should have done that. But Mark was still dabbling in SSM on Hoosiers earlier this year, and I had no intentions of taking anything to Solo Nats, so we just went up more on a dare than anything else.

CAM classes: CAM-C had 27 drivers, CAM-T had 11, and CAM-S had 21. After the 3 runs were over for day 1 we had both fallen to mid-pack, 11th and 12th out of 21 in CAM-S, and almost 2 seconds out of the lead. That night someone told us that a cone was found for another CAM-S competitor ahead of us, so we moved up to 10th and 11th. Not a good place to be heading into day 2, but I was doing the rain dance and hoping for a miracle - which is what we would need to move up significantly.


We didn't walk the East Course until the end of the day on Tuesday. I won't walk the 2nd course in a 2-course event until after the 1st course is done, to keep my mind clear. We walked this one again Wednesday morning.

This course flowed better and was much easier to see. I enjoyed this course better even with the wet and dry conditions.

I worked course while Mark worked Impound, and the skies looked pretty bad in first heat. The entire heat 3 was CAM cars but we got a few STX drivers to help us work on Day 2, to balance out the worker load. I got paired up on corner with the head of the STAC, who had some great comments about the Street Touring category - which I watch closely and raced in for 5+ years (STU) starting back in 2005. We stayed dry the majority of this heat but it started to sprinkle at the beginning of 3rd runs, and really started to rain in the closing minutes.

After heat 1 we went back to the trailer to stay dry and the rain came down hard in heat 2. C-Prepared was running and the wet conditions really shook things up. I was hoping for a continuous light rain, to keep course wet but still driveable. It stopped raining about 30 minutes before we needed to head up for heat 3. That's right when my sister called and told me our father had died. This was a huge shock and it messed with my head. A lot. I had to drive in less than an hour so I tried to wrap my brain around driving, visualizing the course, and thinking of ways to catch up some time versus other CAM-S drivers.

Mike "Junior" Johnson's flared C3 has LSX power, giant Rival-S tires, and weighed in at 2934 pounds. He took 3rd in CAM-S

The grid area was sopping wet but the rain had stopped as CAM gridded up for heat 3. There were substantial puddles on course, mostly on the right side... which was the start and finish areas. The rest of the course was still wet but the wind and sun were drying things quickly.

Richard Jung's CAM-S 1968 C3 Corvette also has LSX power and tips the scales at 2950 pounds

I went out first (I was 99 to Mark's 199) and it was still very wet, but I pushed the car hard trying to set an early quick time. I hit the first cone in the first slalom but had a decent raw time. A number of other driver's had cones on their first wet runs, too, but Mark managed a clean and faster run in the later part of the first runs - he was the last car to take the course for CAM-S each time, being # 199. This moved him right into the trophies, so we had some small hope there.

Run 2 was getting dry on the left half of the course but still sopping wet on the right. I dropped 3 seconds into the 69.0 range but again, hit the same cone in the first slalom. I wasn't even aware I was hitting it but the cone sheets don't lie. Mark went even quicker with a 66.5 time on his 2nd run, solidifying his trophy position around 5th place now, even better.

We go into run 3 and I am sitting on cones and I really need a "hero run" - finally clean and much faster. All of the CAM drivers are dropping several seconds per run as the course dried out, and the 2nd drivers are seeing even drier conditions than the 1st. I was the final "1st driver" to take the last run on West course and I gave it all I had. I dropped another 3 seconds to a 64.102 second run, which felt incredible. If the video would have worked for our last runs I would show it... it was precise, faster, and I felt good about it. This run moved me into 5th and final trophy spot as I came across the line, and I gave a hoot and a hollar!

Mark had the driest look at this course in CAM-S, and he dropped 1.6 seconds to a 64.917. But by then the 2nd driver CAM-S times had dropped into the 63 and even 62 second range, so he fell out of the trophies and down to 11th. At the end of heat 3 my 3rd run was the 6th quickest in class, but I was too far back from day 1 and finished 7th of 21, one spot out of trophies by .277 sec. Here are the Official Results.

Shawn Lambert and Eric Brown took this 2002 C5 Z06 to 1st and 5th in CAM-S class on BFG's... this tire took 1st-12th in class


We went back to our paddock spot, a little down but glad that one of us could catch up a few spots. Mark said he was happy with finish in his first ever Solo Nationals, but I'm never happy with anything other than 1st, hehe. We went to lunch as the sun came out, which made the site a humid and wet mess, grabbing some mediocre Mexican food and plenty of water. We had time to kill before the banquet, which was slated from 5:30 until 10 pm.

After our 2 hour lunch break we came back, loaded up the Corvette and packed the trailer for the drive home Thursday morning. We got cleaned up at the hotel, made it to the banquet hall early, and talked to dozens of folks. Right as the "banquet chicken" lines opened up for the Tues-Wed banquet, we eased our way out of the hall and again went to the Haymarket for Indian food at The Oven, which was amazing. We ran into some Texas Region SCCA folks and shared a table with them.

Thursday morning we hooked up the F-350 to the trailer and said our goodbyes. Apparently there was a MASSIVE rain storm some time after we left - 2 inches fell in 20 minutes - and some associated controversy over the event stopping, some drivers getting dry runs before/after the rains, etc.

Texas Region's Feras Qartoumy built this 72 Nova at home, but "don't call it the Murder Nova"

As I write this at least 5 classes are still under protest or appeal, but eventually that will get that sorted out. I do dislike the "some wet / some dry" runs in the same heat, but its Nebraska in September - IT ALWAYS RAINS.

Keith Lamming in CAM-C had an unusual thing happen to him on course: airbags exploded. This is a known issue in the 2010-11 5th Gen Camaros, where high grip slaloms will trick the car into thinking it is going to crash and the curtain airbags deploy. Keith said he normally removes the air bag fuse before any autocross run but simply forgot this time and it "did what they all do" in autocross. This isn't a thing on 2012-15 5th gens, apparently.

Long time Optima racer Todd Rumpke passed away early during the week of Solo Nationals. He was 53 when he lost his battle with cancer last week. There was a big tribute to him at LS Fest this past weekend where Danny Popp drove his C6 Corvette in competition. I remember Todd from when I raced against him at OUSCI. The news hit everyone hard.

Tony "Rosco" Rietdorf was at Solo Nationals and ran the CAM Challenge in his SN95 Mustang. Sunday night after the Challenge he fell off the back of a golf cart in paddock and his head hit the concrete. An E.R. doc was on the scene within seconds but Tony was unresponsive. The EMTs arrived quickly and he went to the hospital where they induced a coma to reduce brain swelling. There was a GoFundMe page created to help pay for his medical costs, which is still up. We got news last night that he passed away. So sad that a freak accident in the paddock could claim the life of a 36 year old so quickly. Just sucks.

I also lost my father the same week. Its complicated... but I didn't have much of a relationship with him, nor did my sisters. Still sucked hearing this news, which was unexpected. Throat cancer took him at age 75.

And on that positive note... let's wrap it up!


The "drive home from Nationals" always ends up where massive bench racing and planning happens, and this exercise is fun. I dreamed up no less than 4 cars "I need to build" for the 2017 season, two of which were CAM cars, but the reality is that... maybe one of them will get funded and built. I've got the manpower and the know-how to do more, just not the budget to build a fraction of what we can dream up.

There are some plans for Mark's C5 still in process, which I'm not allowed to talk about just yet. I was going to bring his C5 back to Vorshlag after Nationals but Mark had an OKC autocross the following Sunday (today), so I dropped it off at his place and we will get our hands on it sometime in the near future.

The pending rules changes (or not, we shall see) in CAM might prompt Mark to stay in CAM-S. If either the 650 pound penalty for C4/C5/C6 and Vipers goes away or they move to CAM-SS, he might stay in CAM. Otherwise he might move over to SSM and play with Hoosiers and aero. We shall see sometime in November when Raleigh releases any new rules for CAM. I will write up another entry here when we know more, or when get to play with this C5 - or another C5/C6 - in the future.

Thanks for reading,
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