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Unread 03-30-2015, 05:08 PM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default 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 at 05:48 PM.
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