Horses of a Different Color

Driving any two cars back to back with the expectation to perform consistently is a tall order, especially when those cars are as different as production vehicles can get. How does somebody find the limit in a lightweight, unforgiving midengine car that needs to be cajoled for a fast lap, then sprint across the pits to strap into a heavy, powerful, front-engine machine, which must be manhandled to extract its last 10 percent? How does one time-pressed driver update his software so rapidly so as to be able to set searing laps in consecutive sessions in different machines?

Over the last year, NASA Arizona Time Trial driver Eric Kennel managed to do just that. He’s come to love his edgy and excitable Toyota MR-S — the economical midship he’s run in TT6 for the last few years. However, before he started understanding midengine driving dynamics, he dominated TT4 with his 1994 Acura Integra.

Now, the Integra isn’t the front-engine car mentioned in the opening paragraph. Thanks in part to the success he enjoyed in his Integra, Kennel became a highly requested instructor in the Arizona Region. One of whom, a fan and fellow Time Trial driver, gave Kennel the chance to sample their TT1-spec Corvette after bumping into one another at Podium Club. Truth be told, Kennel was a bit intimidated at the sight of John Pearson’s bright green C6 Z06, but he didn’t decline when Pearson threw him the keys. Pearson had just stuck a new GM CT-525 engine in the car and wanted to see what it was capable of.

The prospect of performing in a 550-horsepower Corvette with aero and slicks is a little daunting for someone accustomed to the low power and benign handling of an Integra, but Kennel was surprised to learn that the big Vette was much more forgiving than its appearance suggested. Kennel, with his home-track advantage, went on to set a scorcher of a lap. “It took me a session, but I ended up going 8 seconds faster than [Pearson] had ever gone there — he was just learning the track that day — and the rest was history!” Kennel laughed.

After that fateful afternoon, the two decided to rewrite some of the local records in Pearson’s monster. Kennel joined Team Auto Solve and agreed to turn the laps and aid in the development of the Vette, coach any new members of the team, and lend a hand with tires and brakes when Pearson was pooped.

With Pearson providing the TT1 car and covering most of the expenses, Kennel figured he’d spend half the track day in the Corvette and the other half in his economical MR-S, saving money and getting his big-bore thrills at the same time. An exciting proposition, but one that came with a certain amount of complexity.

Dual Duty

The differences between the two cars are considerable. Big, powerful, and pushy versus small, anemic, and agile. They place different demands on the driver, they must be manipulated differently, and they respond differently to modifications. In Kennel’s opinion, the Toyota is the harder car to extract the last 10 percent from. It’s also been much harder to set up.

The MR-S is always on the verge of oversteer in faster corners — and this can make it an unnerving car to learn. At first, the car was almost undrivable in fourth-gear corners and anything faster. Kennel learned to soften his inputs. Then, to stabilize the rear, he made sure the rear axle had a little more camber than the front. Following these changes, he added an MFactory helical limited-slip diff and a set of low-torque Raybestos ST43 pads. As he discovered, hi-mu brake pads would upset the rear if the middle pedal was prodded too roughly.

It wasn’t a sub-par ABS system causing this, either. The ABS is fantastic and the braking zones are pretty short, but the ABS is particularly sensitive to pad selection. When running mismatched pads, the ABS wouldn’t work well. On matched pads with medium bite, it handles weight transfer well, but it dances its rear a little under trail-braking. Any ham-fisted inputs will be penalized with a snap of oversteer. To get the most from the ABS, the car must be straightened before the binders are applied. Brake hard with any steering input and the rear wants to sashay.

Because of its nervousness, Kennel’s hands need to be especially swift to keep it under control. Any extended lifts off the throttle in the middle of a corner result in a slide, so he’s learned to crack the throttle open when turning into faster corners.

“The midengine platform likes a lot of maintenance throttle to keep the back end planted,” he said. “It also helps limit steering inputs, since lots of steering input at high speed is a good way to end up backward. If it snaps on you at 90, you’re going for a ride!”

The MR-S is excitable and its outright levels of grip and power are comparatively low. These traits mean the car needs to be pointed early. It’s easily agitated in the turn-in phase, which, if done correctly, can help encourage considerable rotation. If Kennel has the direction change completed by the middle of the corner, he can get on the power extremely early.

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Getting the utmost from the car is never easy since it’s so easily excited and potentially overdriven. Operating within that narrow window is a challenge that requires complete focus, but when he’s switched on, he gets that satisfaction that only the most exacting cars can offer.

It may come as a surprise that the Corvette is the blunter tool. However, it poses a unique challenge to its driver. Though the Corvette doesn’t operate on a knife edge quite like the roadster does, it has two times the grip and three times the power.

Softer Edges, Higher Limits

Greater outright grip combined with a reassuring balance means that the Corvette must be hustled — almost manhandled — into the corner, not cajoled. “The Corvette can be thrown hard into corners, unlike the MR-S,” Kennel added.  Even at high speeds, if Kennel is courageous enough to find the limit, he’ll be rewarded with a comforting sort of understeer — the kind that can be neutralized by a brief lift off the throttle.

Managing this forgiving understeer, especially at turn-in, is surprisingly difficult after getting to terms with an oversteering car. “It takes a lap or two to retrain the brain. At first, you just can’t believe how much grip the Corvette generates, especially in higher-speed corners. On slicks with aero, the car cornering much faster than the MR-S, retraining your brain to enter a corner with no fear at a hundred miles an hour can be intimidating,” Kennel elaborates.

As the speeds increase, the amount of front-end grip tests bravery more than finesse. “It really is something you have to work up to. In the bowl at Chuckwalla, for example, I’m telling myself to be brave every lap. The car carries 1.8g consistently in the faster corners, so you really have to ‘sack up’ at a certain point,” he describes. The car is so stable and compliant at those speeds — the Penske 8300 coilovers are truly outstanding — that almost nothing he does, no matter the surface condition, will cause a snap at the rear.

Once he finds faith in the car, Kennel increases the turn-in speeds until the front starts to slide. Then a coast period follows, during which he momentarily lifts to help restore some neutrality, then, as the front starts to rejoin the intended line, he applies the throttle quite assertively. “The engine doesn’t make enough power to spin the wheels in third gear, so, after tip-in, I can apply the throttle without wheelspin in most medium and high-speed corners.”

In second gear, wheel-spin is only a few millimeters of throttle travel away. Even if the wing is pressing the Pirelli slicks into the pavement, Kennel can use generous amounts of throttle to rotate the car as long as he’s selected second gear. This helps him shorten the mid-corner coasting phase and lengthen the straightaway. This throttle application is the greatest generator of rotation.

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The difference between this V-shape corner and the ones he takes in his MR-S is that, in addition to using wheelspin instead of weight transfer to encourage yaw, he can do this at much higher speeds in the Corvette, which goes to 90 mph in second gear. At that speed, the MR-S is in fourth. As a result of all this, he’s usually applying the power somewhat later in the Corvette than he ever is in the MR-S.

Weighing in at 3,175 pounds with driver, it’s roughly 800 pounds heavier than the MR-S. Even with top-shelf AP Racing 9660 brakes and lots of aero, the Corvette doesn’t stop quite as confidently as the lightweight MR-S does — its mass is noticeable.

However, the greatest limitation is the sub-par ABS. Its old Delphi system isn’t the dependable thing that the Toyota’s ABS is, and so Kennel has to tread carefully, particularly in corners that require a long trail-brake. Push too hard, and the Corvette will go into ice mode. “It goes from stopping decently to hardly stopping at all,” he warns.

Practical Problems

If he has time between sessions, he sits and ponders the task ahead in fine detail. “I try to run through visual laps in my head, making note of how each car brakes, and how I can use the brakes and the steering wheel to my advantage in each car. I like to run through one entire lap in my head in each car before heading out.”

If he’s hopping into the Corvette, he’ll have to reassure himself that, regardless of what he does, the rear will stick. Bravery is paramount. If he’s moving into the MR2, he’ll have to soften his touch somewhat, since his finesse is what makes the difference.

Once in the Corvette, finding a clear, quick lap is a matter of careful spacing and an aggressive warmup lap. The Pirellis Hards are durable and consistent, but they usually take two laps before they’re at operating temperature. “They just get better as the session wears on, but some of my best laps get ruined by traffic, because the Pirellis are just starting to get into the sweet spot two laps in, which is when we’ve caught the back of the pack.

“In contrast, the MR-S is good to go by the second corner. The Toyo RRs are as good on the track as they are on an autocross. However, they are sensitive to pressures and surface texture. The rear tires can overheat depending on track and starting pressure, but that’s mainly because of the drivetrain layout. If we see this, we’ll lower the starting pressure, and they’re usually fine for 30-minute sessions.”

Moment of Truth

The duo plans on bringing both machines to this year’s NASA Championships. Both need a little work before they’re optimized. The Corvette can stand to lose 175 pounds and dial some of the push out of the setup. The MR-S’ rear stability needs improving before he feels he can coax everything out of the car consistently. Giving it rear downforce would pose a problem, though, as he’s currently taking advantage of the BTM Aero benefit. “I would have to take a staggering 1.4:1 power to weight hit putting on a rear wing. The BTM Aero gives me a .4:1 bump, and adding a wing removes that while also hitting me with a 1:0 power to weight hit, as per TT6 rules.”

The important point is that they’re not daunted by the task of taking two different cars to the NASA Championships. They’ve learned how to get the most from the cars on track, and they’ve figured out how to delegate the various tasks in an efficient manner that leaves them with the time and bandwidth needed to extract the most from two very different vehicles. In fact, they’re considering adding to the Team Auto Solve garage. Nice to know they’re up for another challenge.