Maxing Out a C7 Corvette for Time Trial Competition

After Allen Patten’s rapid rise to Time Trial success in his A90 Supra, he jumped into the GT4 variant of the Supra. Once a driver’s gotten a taste of a purpose-built race car, it’s hard to go back.

That said, there’s still something so fun about building a car, and with his newfound knowledge, Patten decided not to give up on modding a street machine, but this time, he would avoid doing anything in half measures. For that reason, it made sense to find a less compromised, less luxurious base to build upon.

“The original plan for 2024 was to run Time Trial in the street Supra, but we’d started to find the limitations of the car,” Patten began.

After the exhaust came loose at Lime Rock and melted the e-diff wiring as well as rear wheel speed sensors, they decided to rewire the entire car for motorsport-grade ABS and a few other goodies. That forced them to find a way Patten could stay fresh for the few times this year he’ll be able to test the GT4 car. It’s hard to set up GT4 test days, after all.

Besides, finding a place for the 600-horsepower street Supra was getting more and more challenging. As friend and technical advisor Chris Drum reported, “the car just teleported between corners,” which made it harder to test at casual track days.

As they drew out a plan to professionalize the street Supra, Drum suggested Patten stay in the seat with a simpler car better for accumulating laps. A Chevy die-hard, Drum was confident the C7 Grand Sport was the best seat time car for Patten.

The C7 generation represents a larger jump from the previous generation than the C6 does, and the Grand Sport variant takes the widebody of the Z06 without the Z’s Roots-style blower heat soaking. Compared to the Supra, the Corvette is far less compromised. Double-wishbone suspension, no torque converter, and a dry-sump, direct-injected LT1 engine that makes 460 horsepower at the crank certainly didn’t hurt.

That Old Cliché

“It was just supposed to be a seat-time car: something fun, reliable, and sweet, but the plan to keep it stock didn’t last long,” Patten said with a laugh.

When he decided to prep it for NASA TT3, Drum turned him to Louis Gigliotti for his basic track-day handling package: a set of proper two-way Penskes, as well as Gigliotti’s drop spindles, and his spherical bushings. “That package is pretty much the Corvette easy button,” Drum quipped.

The wider bodywork could easily fit a set of Apex SM-10RS wheels measuring 18 x 12.5” at all four corners. Though another 30 cm could be stuffed in there, they opted to run 315-section Hoosier A7s to avoid a penalty in his chosen class. The basic track package was a revelation.

“I don’t know why I had this notion that it would be scary, but with the transaxle and the weight distribution, it’s so natural to drive. With the double wishbone suspension and drop spindles, it maintains geo well – you don’t have to throw five degrees of camber at it like you do a strut car. The braking performance is amazing, too. The performance out of it with minimal mods blew my mind. That led me to want to explore building,” he elaborated.

The car came with the lower-grade iron brakes, but with Girodisc two-piece rotors and Hawk DTC70 front and DTC60 rear pads, it stops quite well.

The engine needed little to make more than adequate power. Mainly to improve power across the rev range, they added a ported MSD intake, Stainless Works headers, and a throttle body from an LT5 motor that powers the C7 ZR1. In total, it made 470 wheel horsepower, though this had to be detuned to for TT3, obviously.

The factory gearbox lacked a little precision in the shifter throw, and the higher gears were too tall for Patten’s liking, so in went a C7 Z06 gearbox, which has a better ratio spread, as well as a short shifter.

Broken Box

“Whenever I get a car, I have a stupid obsession with optimizing it. I raised the stock redline from 7,000 to 7,200 since I wanted to flat tune it. All that fine-tuning didn’t pay off. I ended up bending a pushrod when street-testing it. Funny – my seat time car got torn down before I got to drive it on track.”

When he got it running again, he took it to a NASA event at Virginia International Raceway with the intention of beating the TT3 record, a 1:58.6 set there by a lightweight E46 M3 with aero. After detuning the motor to 375 average horsepower, they added a bit of ballast to bring the total weight with driver to 3,601 pounds.

On a set of non-sticker A7s, they put in some promising times in the low-59s the first day. but, during one particularly promising lap, Patten money shifted it and blew it up again.

The team pulled an all-nighter trying to get it fixed. They thought it was a pushrod, but it was a bent valve. When they took the cylinder head off, they drove to Mooresville to pick up another one that night, but once they got the new one on, “one of the threads in the aluminum block stripped, because this was the third time that head had been off,” Drum noted.

Pushing the car in a competitive setting helped confirm that modifying the seat time car was worthwhile. “The C7 is a little easier to drive than the Supra. It’s got a longer wheelbase – more neutral. The easier you can make it to drive, the faster you can go in a Time Trial setting with limited seat time, where you don’t have a whole crew to optimize the car.”

Never Say Die

A few weeks later, they went to CMP for redemption. Even with some transmission issues, they were looking strong at the start. Following a few damping adjustments for low-speed rotation, they also reduced a little compression at the rear to improve with longitudinal grip. In addition to composure over CMP’s high curbs, good drive off the corner, especially in Turn 14, is vital.

“Even without aero, I can stay flat through the Kink at CMP. I try to have to turn in slightly later and jump the curb with the car straight, because if you hit it with much steering angle, you’re going to have a bad time when you land. I mean, you’re four wheels in the air at 125 mph!” he exclaimed.

“There was some more in it there, but with the ice mode kicking it from lap to lap, it saps a little confidence. It varies lap to lap. Basically, it gives you a hard pedal and about 30 percent braking torque. If you’re threshold braking, the only way to cure the ice mode is to cadence-brake — not that easy in a heavy car.”

Even though he something left on the table, he set a new TT3 record there. A year prior, he took the TT2 title in his Supra. This lap, he found, came much more easily to him.

“The Corvette rotates more easily than the Supra, so naturally you’re a little straighter at exit, which makes it seem like it puts the power down better. With the stock-power Supra, the traction issues are manageable, but with big power, the turbo lag and the torque hit become factors you must consider. The window is much tighter with the big turbo, whereas a big V8 with a natural power band is much more forgiving.”

However, it’s just as much the setup as the approach he’s taken in recent months that have gotten him to a record-setting position. Drum, who works alongside IMSA pros on a regular basis, is impressed with how Patten has developed as a driver.

“He usually finds time in whatever he gets into. He describes feedback well. Good at analyzing data, too. Once you tell him something, he can do it – sometimes he can put several things into practice simultaneously. You don’t have to worry about him retaining information and doling ideas out one-by-one. He works harder than any other club racer I know. He cares. He races sims, he races karts, he spends a lot of time thinking about racing, and he doesn’t have much fear. He’s a consummate student of the sport,” Drum said.

Ruined Now

With one record set, they had to take the car down a new path. The motor had been giving them problems again, anyway, so it seemed like the right time to take a new powerplant — one with near-OEM reliability — and let Gigliotti work his magic on it.

For this version of the car, they opted for a mostly stock LT4, the supercharged 6.2-liter from the Z06. Thanks to Gigliotti’s extensive cooling upgrades, which total something like 5.5 gallons in capacity between the radiator and the blower’s heat exchanger, this shouldn’t heat soak like the factory version. Lubrication comes courtesy of a Dailey six-stage dry sump.

With a COMP cam, Frankenstein Engine Dynamics cylinder heads, a Kong Performance-ported blower, and Gigliotti’s side-exit headers, the LT4 is expected to make upward of 800 horsepower on factory boost – just 11 pounds. Detuned for TT1, the package should make something around 540 wheel horsepower at 2,900 pounds.

No expense has been spared. Along with the MoTeC M182 system, which has been designed to retain the factory direct injection, they added a supplementary port injection system for ethanol’s cooling and boost-friendliness.

“The factory direct injection system cannot really keep up with any sort of modded power level on E85, because ethanol requires significantly more fuel. C7Z’s typically run out of fuel system around 700 horsepower at the wheels, and we are well exceeding this. So, we are utilizing the factory direct injection and adding a supplementary port injection plate that goes between the supercharger and cylinder head. We’ll have a fuel system that’ll support up to 1,000 horsepower, if desired,” Drum elaborated.

Whole Enchilada

Now, Gigliotti is going full-bore on this one. With Zebulon’s wing, splitter, and diffuser; as well as Gigliotti’s own flat floor, the car will have real aero.

It won’t have much interior, either. Target weight is somewhere around 2,900 pounds with driver, thanks in part to Gigliotti’s custom engine harness, which weighs 7 pounds total.

Braking power will improve with the AP Essex 9660/9450 brake kit, Bosch Motorsport Clubsport ABS, and an AP pedal box as used in the Next Gen Cup Car. The braking system alone rivals a new economy car in price.

“After driving it a few times, I fell in love with the Corvette platform. That’s why I decided to get behind this and put the street Supra on the backburner,” Patten said. “Now the Supra is a bare shell. I’ve got too many irons in the fire with GT4 stuff, so I’m probably going to move on and part it out.

The Corvette has been a mixed bag. The wider aftermarket and superior suspension design have facilitated its development. The performance and the potential are there, undeniably. In terms of reliability, the Toyota might have the edge, though.

“In my experience, and I don’t want to generalize, I’ve had reliability issues with the stock driveline,” he said. “The money shift was my fault, but we had the head off three times and I’ve only been to the track four times with it.”

As frustrating as the start has been, the potential has been clear since day one. Now, with real money behind the build and some of the best Chevrolet club racers in the country at work on it, there’s no doubt Patten’s newest Time Trial creation will reset more than a few records. Where it’s headed, he’s not quite sure — GT4 obligations have him flying by the seat of his pants these days — but wherever it ends up, the combination of car, team, and driver will make waves.

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