Developing A C8 Corvette For Time Trial Competition

Even after a fiery crash, which burned his cherished C5 Corvette to the ground with him in it, Mark Petronis’ desire to race had not been extinguished. Petronis could have walked away from the sport after the crash at New Jersey Motorsports Park, but fate had another ‘vette in store for him. “Much to my wife’s chagrin, one of the first things I asked myself after waking up in the hospital was, ‘What am I getting into next?’”

Petronis’ return coincided with the unveiling of the Chevrolet Corvette C8 model. His father ordered two of them in early 2021 — two because he didn’t know how long it would take for Chevrolet to deliver. After flipping one, he gave the complimentary passes to the Ron Fellows school at Spring Mountain — each given as part of purchasing a new C8 — to his two sons.

“It was my first time back in a car, and I had no idea what I would experience mentally or physically. I didn’t know how I’d perform on track with other cars around me. My right hand was still a total mess. I had little use of my fingers,” Petronis admitted.

Learning that he was faster than his brother Kevin and only a few tenths off the instructors abated some of that anxiety.

Soon after, Petronis picked up a C8 of his own and took it to Lime Rock. There, he realized how much more heft he was now carrying around — an additional 700 pounds over his stripped C5.

Neither the added weight nor the stock alignment’s push could diminish his sense of joy, though. The overwhelming sensation that weekend was shock. The car was so good out of the box and the 59-second laps were testament to that.

Bare Essentials

With it being so good, only a few things needed to be changed. “We did a couple of back-to-back tests on stock tires. Stock alignment moves all over the place. Without our camber kit, the factory eccentrics just don’t hold. With a track alignment, the stock tires lasted longer and I went 1.4 seconds faster,” he added.

Around that time, people were starting to track them. Mark’s company AMT Motorsport designed their own camber kits. “The C8 is all cast, and every corner of the suspension arms adjust with round eccentrics; and there are no flat edges. They’re just relying on the torque of bolts to keep the control arms from moving. Our product is basically a stop sign with positive edges that, once locked in, can never move.”

Next came the interior. He ordered the car with GT2 seats hoping they’d be supportive enough, but they weren’t. With AMT’s Ultralow seat mounts, OMP halo seats, a Brey-Krause harness bar, and Sabelt harnesses, he found the security he needed to feel at one with the car.

Following that, he splurged on AP Racing Pro 5000R brakes with 372mm and 355mm rotors, front and rear, respectively. “Unless I’m 100 percent confident on the brakes, I can’t be fast,” he admitted. Along with those caliper and rotor upgrades, he opted for GLOC R18 pads at all four corners.

With the C8’s few shortcomings addressed, he began trying tires. Anticipating a lot of unnecessary movement when he graduated to slicks, Petronis threw nearly-complete monoball suspension at it. The difference was staggering. “There’s not as big a difference on monoballs as with the C5 and C6. The C7 and C8 are quite a bit stiffer from the factory. On the 200-treadwears, the stock bushings go a long way. Yes, monoballs are still a benefit at the sharp end, but not a necessity like they are with the C5/6.

“One thing to note is you can’t add monoballs to the front lower control arms because the steering module convinces the car’s running on rough road and the wheel wrenches out of your hands. It’s untenable,” he added.

With full confidence in the car, he could push it hard enough to start breaking things. One afternoon early in his ownership, Petronis was enjoying a head of steam coming into Downhill at Lime Rock when he spun on his own oil. His engine had blown. The outside wall was approaching fast, and flashbacks from his big wreck came flooding back in.

Fellow NASA Northeast racer Adrian Wlostowski was standing at the Downhill as Petronis was spinning toward the wall with smoke billowing out the rear of the car. Also on scene the day of the accident in 2021, Wlostowski, had saved his life by pulling him from his burning car five years ago. “It was crazy that [Wlostowski] was, yet again, ready to jump the wall and pull me from a burning car one more time,” Petronis joked, “But at this point I don’t know if he’s an angel or a devil, since every time I’m on fire, he’s there!”

Thankfully, the gods smiled on him that day. He missed the outside wall by 20 feet. The icing on the celebratory cake was the free engine Chevrolet provided with no questions asked. Unfortunately, it was a bit “soft,” as Petronis put it — around 40 horsepower shy of the norm.

Back in the car, he started coming to terms with the mid-engine balance. “I mean, the technique is not wildly different, but the brake release is more exacting. “In Race 1 mode, you lose yaw control, and on cold tires the car can snap on you when coming off the brakes. When it starts going, it wants to keep going,” he elaborated.

That rotation needs to be capitalized on. “With so much grip in the rear, the point is to get the car rotated as quickly as you can so that you can stand on the gas. It’s not a matter of feeding the power in sooner. It’s about rotating the car earlier and standing on gas.

“Unlike the C5, there’s enough traction to put the power down immediately. The thing just hooks up and grips. The mid-corner speed is maybe a smidge slower, but the acceleration more than makes up for that on the delta. My coach Ricky Taylor helped me get to terms with this,” he continued.

With the interior, chassis, and brakes sorted, Petronis and his team went to work on the aero. That’s when he got Ryan Neff of Zebulon Motorsports Consulting involved with the project. Neff provided the CFD for Faircloth, whose wing is currently mounted to the rear. The first rear wing was a 72” x 12” Faircloth element with their own mounting system, which he matched with an LG splitter at the front. Adding just the wing dropped 1.4 seconds at Palmer Motorsports Park, but the balance was rear-biased and a touch pushier than Petronis liked.

They replaced the LG with a co-designed Zebulon splitter that produces almost 300 percent more downforce than the LG. With two trips to the A2 Wind Tunnel in Mooresville, N.C., to verify results, they bumped the rear wing up to a 78” x 14”, which now has the power to balance the crazy front downforce created by the Zebulon splitter. It’s not often you get a production car with a front end that outperforms its rear, aerodynamically speaking.

“Even with the smaller wing and LG splitter, we were at the limit of what the stock mag ride shocks could handle. Because of how sensitive the electronics are in the car, you can’t just increase the spring rate to support the additional downforce of the car. With our big splitter and huge wing, the car would be undrivable on the factory suspension,” Neff explained.

“It became clear we had to get racing stuff, so we bought Penske 8300 double-adjustables from Louis Gigliotti, one of the best guys for Corvettes. To get the most from them, I had Andrew Acquilante come onboard to fine-tune them,” Petronis stated.

They started at 750-pound springs, then had two further iterations to help support the aero load, because they were “bottoming out everywhere.” They ended up with 1,100-pound springs in front and 1,200-pound springs in the rear. This was enough to support the downforce from the first wing as well as the larger wing that replaced it. Lots of downforce helps neutralize the car a lot.

“A good rear wing helps settle the rear in high-speed sweeper stuff, and the balance is manageable,” Petronis said. “Understeer is easier to deal with at high speed, I think.

“With the C5, I was confident I could handle whatever the car did until about 95 mph. Past that, I was definitely white-knuckling the car when it decided to get a little loose. In the C8, I don’t think it will surprise me at any speed. In fact, I have extra confidence going into the VIR Esses at 140, and I’m sure there’s still some left on the table.

That poise and predictability comes at a price, though. “The tires go a bit faster than they did with the C5. I could run 16 heat cycles on Hoosier A7s and still set records in the C5, but now they’re dead after 12, though the Toyo R that I’ve run extensively seems to last a little longer.”

They may be at the practical limit of weight reduction. “We removed 200 pounds without trying hard. An Antigravity battery and a Paragon exhaust are responsible for a lot of that, with the lightweight seats and mounts accounting for the rest of it. I’d like to take wiring out and save another 200 pounds, but messing with the electronics is asking for trouble.”

Final Touches

Thankfully, it’s not really needed at this stage. The C8 may be a little harder on consumables and a little restricted in terms of tuning, but it works well under hard lapping, even on hot days. “The gearbox and the differential have never gotten over 240 degrees. Some have had over-temp alarms on theirs, but my assumption is that’s caused by running the car in auto mode. Keep it in manual mode and it won’t make any unnecessary shifts, which seems to keep things cooler.”

VIDEO

Ride along with Mark Petronis on a 56-second lap in his C8 around Lime Rock Park.

Keeping the motor cool requires one easy option Americans will have to install themselves. “The middle-east spec cars come with an additional radiator in the driver’s side door, so we added that,” Petronis said. “Before that, you would get one morning session before the car reached 230 degrees, at which point the car was dog-slow due to all the timing it pulled, and that heat soaking tended to last for the rest of the day.

“After we added the fourth radiator, the highest it gets is 226 degrees. It’s only a $700 option — you just have to buy the parts and do it yourself. We don’t need crazy front radiators for the time being.”

However, he might have to rethink that if he’s to improve aero efficiency. “In the short term, I’d like to take aero efficiency to the moon. We’ve taken some inspiration from the GT3 version of the car, which has a massive center radiator with a ducted hood. By adding something like this, we could block off the side radiators, generate more downforce at the front, and reduce drag. We played with all that in the wind tunnel, and there are definitely gains to be had.”

With the car now fully sorted, Petronis feels they have addressed all the low-hanging fruit available for the platform. “Sure, we could try to add some power to make up for those missing 40-odd horsepower, but we’re going to chase crazy aero efficiency with a flat floor and big diffuser,” Petronis said.

“It’s going to be an expensive undertaking and probably in no way marketable, but we’re pretty excited to have the most aerodynamically developed C8 in existence outside of the GT3 cars!”