Last week we introduced you to our Classic American Muscle CAM-S autocross project car, a 2003 Chevrolet Z06 Corvette that had been breathed on by legendary tuner John Lingenfelter. While starting with a car that came out of the Lingenfelter Performance Engineering shop would reduce our need to look for much more power, it didn’t take long for us to discover that with most of the work being done more than a decade ago – and the car had been well used since its creation – we still had a good deal to work to do.
We squared away what is probably the most important part of any autocross build during our previous installment. Last month we came up with a creative suspension solution by combining Motion Control Suspension, Eibach, and Hellwig suspension components, and then topped that off with a custom set of Forgeline wheels wrapped in massive BFGoodrich G-Force Rival S tires. Now it was time to focus on other areas of improvement.
One issue we discovered during our initial shakedown runs was the Corvette’s poor braking performance. Considering the car was outfitted with a beefy Alcon brake system consisting of 6-piston calipers up front and 4-piston rears, all clamping down on two-piece, 14-inch rotors, we really expected the car to at least stop as good as a stock C5. What we discovered, however, was braking performance more on par with a 1980s sedan.
Digging into the brake system, we believed the lack of stopping force was a result of a mixed set of brake pads, which included both ceramic and semi-metallic. While our CAM project primarily focuses on autocross, we also plan to do some SCCA Time Trials; consequently, we set out to find brake pads that would allow us to do a range of events without necessitating a pad change from venue to venue.
Reaching out to Ian Berwick, PAGID Racing’s motorsports manager, yielded us the pad we were looking for. “I’d recommend the RSL29 compound,” Berwick told us. “It’s easy to use, beds-in well, and works well with ABS, meaning the modulation and release is very good.”
Picking a pad compound was only half of the process; next we had to identify the pad shape that married up to our nearly 15-year-old Alcon brakes. Tracing the old pads and sending a scan to Berwick quickly narrowed down our options. Here’s a tip: If you use this method to compare pad shapes, place a reference measurement on the page since scanners can marginally resize the image. Also, since we couldn’t be sure that the new pads would be compatible with the transfer layer that was already on the rotors, we had West Coast Race Craft clean the rotors.
Make some noise
Another item that needed some TLC was the exhaust. While the car was already outfitted with a very nice, one-off titanium turbo back exhaust system, it was loud. Much of the reason for this was the air-to-liquid intercoolers, which occupied the space where mufflers are typically found on a C5 Corvette. The system included a pair of metal core catalytic converters and resonators, but no actual mufflers.
With limited space for mufflers, we ditched the resonators and asked the team at Burns Stainless to build a set of mufflers to fit in the same location. With the proximity of these mufflers to the engine and turbo chargers, we selected the optional scrubble packing from Burns, which is better suited to this kind of temperature range than the standard glasmat packing. In short order, we had a set of lightweight, custom length mufflers that fit perfectly in the space previously occupied by the ineffective resonators. Both the tone and volume of the exhaust were much more pleasing after the change.
Sit right there
If you’ve ever driven a C5 Corvette in anger, you will have noticed that the factory seats are about as sporty as your dining room chair. While it may be comfortable enough to sit in for hours, spirited driving is a pain. It was time for an upgrade.
Like with many sports cars, finding a race seat that will fit and retain the interior can be a challenge. Luckily, we had just learned of a new offering from Sparco USA that was supposed to address these tight cabins.
The FIA-approved QRT-R utilizes Sparco’s QRT ultra-light technology, which greatly improves the strength-to-weight ratio of the seat. In addition, this design offers the interior dimension of a larger seat while maintaining a compact outer shell that fits more easily into small cars.
Having spent far too many afternoons fabricating custom seat mounts, we opted for the 600 Series mount offered by Sparco for the C5. Sure, mounting a race seat seems easy on the surface, but anyone who has done it quickly figures out how much of a time waster it can be – the 600 Series mount makes it a bolt-in affair.
Sparco also offers a range of side-seat mounts and sliders, allowing you to get the seat right where you want it. By the time we were done, we were delighted to see the QRT-R fit our cramped cockpit with room to spare.
The next item to address was a race harness. At some point, our project car had been outfitted with a harness that attached to the stock seat and appeared to have been heavily modified by someone with marginal sewing skills. Between the homebrewed modifications and aged-out stamps on the belts, it was an easy choice to shop for a new one.
We selected the RaceQuip 6-point, 2-inch pull-down HANS/FHR harness. The 2-inch lap and shoulder belts are by far our favorite setup in any of our road race project cars, both for comfort and ease of use – the 2-inch lap belt in particular is a comfortable option. While the 2-inch shoulder belts are designed to be used with head and neck restraints, it isn’t an issue on the autocross course, and any time we hit the track, we are wearing one.
The RaceQuip FIA 6-point belt is a great value, too, priced well below similar harnesses, and the action on the adjuster rivals that of much more expensive units we have used. The supplied hardware made installation a snap, with the supplied clips-ins used on the floor and the shoulders wrapped around the harness bar that was already in the car.
For track use, we also picked up a RaceQuip tow loop with the soft ring end, which will meet the requirements for most track groups, while not beating up the paint on the car.
With the dirty work done, we headed over to FR Sport where Mark DeShon worked his alignment magic. The C5 is blessed with a good range of suspension adjustment from the factory, and we were able to obtain a good baseline setup.
The final stop on our setup tour was a visit to Church Automotive Testing, where Shawn Church utilized HP Tuners software to improve the drivability of our slightly overpowered autocross car. We already had Dynojet numbers showing 715hp and 716lb-ft of torque at the wheels on pump fuel, so we wanted to see if we could soften the initial curve. Unfortunately, this is where the project took two steps back.
Within seconds of connecting the HP Tuners suite to our ECU, Church discovered a big issue. Somehow this car was still fitted with a stock 1-bar MAP sensor, something that doesn’t pair well with forced induction. Also, at some point in its life, the MAP sensor had been turned off and the car was running a MAF-only calibration. While the car was fitted with an oversized MAF sensor, it still could not manage the airflow produced by the twin turbo setup.
With no time to address the MAP sensor, we shifted directions and sent Church on a mission to dial power out to make the car safe to run. Then we hit another snag – around 720lb-ft of torque on the Dynapak (a dyno that attaches to the rear hubs), the Corvette’s clutch began to slip. On the street or even on the chassis dyno, this would be masked by tire slippage, but it was clear as day on the hub dyno.
Less than 24 hours after our dyno session was an autocross, and despite the power and clutch issues, we were dying to get our CAM-S Corvette on course. Do you want to know how the car did? Well, for that you’ll have to wait until our next installment.