Last week we took a closer look at the Classic American Muscle (CAM) autocross category and we mentioned that we were starting a CAM project of our own. But even the best-laid plans are subject to delays, and some of those setbacks forced us to roll out our project later than expected. But here we are – and rest assured, what this project lacks in punctuality it will more than make up for in horsepower.
Our desire to jump into CAM is nothing new. In fact, a CAM project car has been a regular lunchtime topic amongst the SportsCar staff for years. The problem was deciding on the car and how much power we thought we needed. Then about a year ago, I received a call from my father revealing that he was about to reacquire a rather unique C5 Z06 Corvette he had sold only a year earlier. So, what makes this car unique? This is where the story gets interesting.
Not long after this Corvette left the dealer’s lot back in 2003, the first owner sent it to a performance shop in Decatur, Ind., for a few upgrades – the plan was to have Lingenfelter Performance Engineering (LPE) install its twin-turbo package. Then, while the car was in the shop, an invitation was sent to John Lingenfelter to take part in the 2004 Car and Driver Supercar Challenge, an event that would pit top builders and tuners from around the country in a head-to-head battle of power and performance. With the invitation in hand, an offer was made to the car owner that LPE would do some additional work to the car at no additional charge in exchange for being able to use the Corvette for the event.
While we’re unsure of the specific work completed, we do know the engine was fitted with a modified version of the twin-turbo build LPE typically put on the street. According to the Supercar Challenge coverage in the November 2004 issue of Car and Driver, this Corvette boasted 800hp and 830lb-ft of torque, courtesy of a 427ci small block and a pair of turbochargers. To handle the boost needed to achieve these power numbers, the car was fitted with a C5R racing block, featured extensive proprietary cylinder head work, and air-to-liquid intercoolers – all items not found on most of the road-going pieces put out by LPE.
Combined with a massive Alcon brake kit, GM’s T1 road racing suspension package, and massive Michelin tires – which are neatly tucked into the bodywork thanks to LPE’s mini-tub kit – the car was able to pull off a second-place finish in the Supercar Challenge. But that was then.
Over the years the car has changed hands a number of times, even making an appearance in the One Lap of America with one of its many owners. Eventually, the car landed at a commercial equipment auction, hardly an outlet befitting such a car. But this made it easy for my dad, a longtime Corvette aficionado, to snatch it up. “I purchased the Z06 in early October of 2008,” says Robert Isley. “It was at an auction company that handles business and equipment failures for banks. I then took a year to get the car cleaned up and make some needed repairs.”
By the time he acquired the car, much of what had been reportedly installed for the Supercar Challenge was nowhere to be seen. The race seats were gone, the only remaining piece of the T1 suspension package was a front swaybar, and it was shod with a very old set of Michelin tires, some of which were emblazoned with the One Lap of America tech stamp.
After enjoying the car for a few years, my dad sent the Corvette to its next owner. “I sold the car to a buyer in Wisconsin in July 2016,” he says. “The new owner put less than 200 miles on it in a year. He then agreed to sell the car back to me after it sat in his garage for nearly the entire time he owned it. He told me he didn’t drive it because it was way more car than he thought he was buying.”
With the Corvette reacquired, I proposed to my dad that we get serious with the car. Thus begins the Corvette’s second life.
A SECOND LIFE BEGINS
An impromptu trip to Arizona – where the car and my dad reside – found us at an Arizona Region autocross for a shakedown run in the Corvette’s new autocross class, CAM-Sport. Two turns into the first run I could see why the last owner only put 200 miles on the car: the car didn’t want to stop. On top of that, the car was plagued with understeer at every turn, and the rear tires would spin if you even thought about the gas pedal. We certainly had some work to do.
With a ridiculous amount of power on tap I focused on making the car stick to the ground. But with one of the few rules in CAM being a 200-treadwear minimum for tires, it was obvious that suspension would be the most important area to work on.
From the factory, the C5 Corvette is fitted with a mono-leaf suspension. This system has proven effective on Street and Street Prepared Corvettes, but despite that, there are limited choices when it comes to alternative leafs. Additionally, custom leaf springs are very costly and a pain to change. Coilovers can be fitted in their place, but the C5 chassis was not engineered with coilover suspension in mind – the idea of fitting them creates a debate with Corvette owners that can go on for days.
Inspired by some of the Porsche builds we’ve seen – where coilover springs supplement the factory torsion bar suspension – I decided to investigate this option. Since CAM has no suspension restriction, why not think outside the box? As it turns out, at one time Callaway Cars, another well-known Corvette tuner, offered just such a suspension package. While discontinued long ago, Mark Krumme of Eibach Springs was able to obtain some of the specifications.
SUSPENSION OF DISBELIEF
Inspired by the idea of having a suspension package that would be easy to tune, the search turned to finding the right shocks, and Wyatt Gilbert of Motion Control Suspension noted that the MCS 2WNR dampers for the C5 would be a good fit. This package offers a unique and easy-to-adjust mechanism, offering users independent rebound and compression adjustments, and are also outfitted to handle coilover springs. Perfect!
One of the challenges with this particular Corvette is all of the turbo system plumbing, from cooling to charge pipes – almost every spare inch of the car is packed with hot items. The 2WNR dampers offered all of the control and function of a two-way adjustable shock but without having to worry about mounting a remote canister in the tight confines.
The turbo conversion adds a good bit of weight to the front of the C5, so it was decided to increase roll stiffness on that end of the car; consequently, 150lb Eibach springs were added to the MCS dampers. To offset the supplemental spring’s effect on ride height, we modified the OE spring to sit the car lower. This involved both trial and error – and luck – but by the third try, we had the springs working together, the ride height where we wanted it, and the ability to easily tweak corner weights. Most importantly, we could now quickly and easily change the front coil springs to tune the car’s handling as desired.
The next project was to remove the front GM T1 swaybar. While effective on the racetrack, this setup was not ideal for our application. The unit chosen for this build was a reasonably sized 1 5/16-inch tubular swaybar from Hellwig. This would still be a good upgrade over the OE swaybar, plus it’s adjustable, offering up another tuning tool.
At the back of the car, I quickly found what was suspected to be hampering the car’s ability to put power down: the OE rear shocks had been fitted with an additional set of bump stops, perhaps in an effort to keep the 345/30-19 Michelin tires from rubbing on the fenders. Chucking that setup, and with the goal of keeping the rear of the car compliant, the MCS 2WNR shocks were installed sans any additional spring. MCS did supply the needed hardware for supplemental rear springs, however, so should additional spring rate be required, a call to Eibach will solve that problem, too.
Hellwig offers an adjustable rear swaybar, but we chose to retain the OE Z06 unit for this phase of the project.
With the suspension settled on the car, it was time to look at the rolling stock. While the car was outfitted with a nice looking wheel and tire package, it did little for anything other than straight-line performance.
Any effort to harness 800hp on an autocross course requires serious rubber, and when it comes to tires in the CAM category, BFGoodrich Tires G-Force Rival S is the go-to – and, importantly, BFG offers the big sizes. The almost standard package for a CAM-S Corvette is a 315/30-18 in the front and 335/30-18 in the rear, which made the choice easy. Even though these are slightly narrower than the Michelin tires that were already on the rear, it was obvious from our baseline autocross that a modern, sticky tire was needed. Being significantly shorter, the new BFGs also eliminated concerns over fender clearance and they corrected an artificial rake issue.
Fitment in the rear was easy – the front was a challenge. The car had been fitted with a 295mm front tire, and even then there were signs of it rubbing on some of the turbo related components, so we reached out to Forgeline Motorsports for advice on the wheel and tire fitment issues. Forgeline has a massive catalog of race-proven wheels, and a knowledgebase that makes it easy for them to design the right package for virtually any application.
After some measurements, Forgeline’s David Schardt recommended a wheel size and offset that would tuck the massive tires into the fenders, as well as clearing the 14-inch Alcon brake rotors and six-piston calipers that were already on the car.
Based on Schardt’s recommendation we ordered the Forgeline GS1R wheel with an 18×11-inch fitment in the front and 18×12-inch rear. The GS1R wheel is utilized extensively in both professional and amateur road racing, so we knew it could take the abuses of autocross – and with plans to do some non-autocross activities with the car later, the GS1R had the car covered.
The GS1R features a forged 6061-T6 aluminum mono-block construction, with I-beamed spokes, providing a combination of strength and stiffness – and it doesn’t hurt that they look incredible. Our set was coated in a dramatic Pearl Gray finish and included the optional center caps.
To help ensure that this new wheel and tire package would no longer rub on any of the turbo plumbing, we had West Coast Race Craft build a set of custom steering rack stops.
As it turns out, the new 315mm front tires safely cleared the important turbo bits in the fenders during normal use; it was navigating tight spots in the paddock that proved problematic. Regardless, the new steering stops eliminated the issue all together.
THERE’S MORE TO DO
The problem with this project is that this Corvette is very custom to begin with, so very few off-the-shelf components will do the job. Simply installing suspension, wheels, and tires took months of calling experts, measuring, planning, measuring again, ordering, and then waiting for parts to arrive. And the project is far from done.
What remains? Horsepower tweaks for one, perhaps in the opposite direction of what you may think. It turns out, while ridiculous power is fun, usable power is better. There’s also the problem of slipping out of the driver’s seat during autocrosses to deal with. Much of that will be dealt with in the next installment, although I have to admit, dialing in the power is turning into as much of a monster as the power itself.