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Unread 03-30-2015, 05:08 PM
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Default Vorshlag C5 Corvette Development Thread

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 at 03:55 PM.
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