Driver Battles: RX-7 And C6 Grand Sport Square Off At Willow Springs

It’s a sad sign of the times when big egos get to hog the spotlight in grassroots racing. The old racer camaraderie so many of us experienced at one point in our lives seems a rare commodity these days, and it’s seldom seen when budgets go sky-high. Fortunately, there are still a few series that encourage friendships to blossom and skills to improve.

When Johnson Mac and Steven Kronemberger arrived at Willow Springs earlier this year for Driving Line’s “Driver Battles,” they both felt slightly ambivalent. The relaxed setting contrasted with their competitive natures, the daunting high-speed corners, and the standard of the circuit-oriented cars. One with a rotary, the other with a V8, these two drivers pushed themselves a little further than they felt comfortable, but they still left the circuit with a broad smile stretched across their faces.

Photo credit: Luke Munnell/Driving Line

Representing the Rotaries

For the last 20 years, Mac has adored the Mazda RX-7. Running laps around Trial Mountain in Gran Turismo hooked him on Mazda’s rotary-powered racer. By the time he was in college, he had made a second-generation RX-7 his own. After his first autocross event, the bug sank its fangs deep, and this “hair-pulling hobby” became one of the driving forces in his life. It was only natural that, in 2015, he moved onto the third-generation version of the RX-7.

A Shine body kit adds bold touches to the RX-7’s feminine shapes.

Mac’s friends at Lucky 7 Racing built this ’93 RX-7 for a customer who ended up moving out of state. As the Lucky7 owner didn’t want to part this gem out, he made Mac an offer to take it off his hands. Soon after Mac rolled this white gem into his driveway and tidied up a few loose ends, he took this street-legal track car to Willow Springs for its first shakedown to better understand its makeup.

Powerful, Compact, and Surprisingly Solid

Its 13B-REW engine is extensively reworked for reliability, tractability, and plenty of grunt. A serious streetport, an Exessive MFG lower-intake manifold, and Turblown TDX62R turbocharger help provide the motor with all the air it can consume. A Full Function’s fuel rail, ID1000 injectors, and an Aeromotive Stealth 340lph pump quench the rotary’s thirst.

To function under immense stresses, Mac installed E&J 3mm apex seals, twin Earl’s 19-row oil coolers, an AC Fabrications V-mount intercooler, and a Haltech Elite 1500 ECU. The whole package produces 410 horsepower at the rear wheels, with a meaty midrange and a linear delivery, it makes the 13B-REW perfectly suited for the road course.

The 13B-REW squeezes an impressive amount of power from a microwave-sized motor.

Despite its reputation, a relatively mild build keeps the motor fairly reliable. “I wanted something I could improve my driving skills with, and not something I’d have to wrench on Sunday night before the work week started,” says Mac. Wise words.

The RX-7 is stabilized by a Shine RE rear diffuser, an EVO-R GT2 rear wing, and a homebuilt front splitter.

Supportive Footwork

When he does get on track, its friendly temperament makes this RX-7 easy to drive. Underneath the widened rear sit 275-section Nitto NT01 tires, Megan Racing rear lower control arms, Superpro bushings, and the factory Torsen differential. These touches are enough for strong traction in most situations, though there’s always enough poke available to get Mac into some trouble.

Despite the mild push, Mac still enjoys the accurate steering the third-generation RX-7 is known for. Big 275-section NT01 tires in front, the ideal weight distribution, and a compact motor well-behind the front axle mean Mac only has to think his way towards the apex, and he’s there. Still, with the grip available and some of the long corners present at his favorite tracks, Mac eventually had no choice but to reinstall the power-steering system. “My arms were falling off at the end of track days,” he laughs.

Weighing just 2,800 pounds with Mac in it, the RX-7 can get away with a relatively modest brake setup. Under the Volk TE37 wheels, the factory four-piston brakes are fitted with Stoptech rotors, Hawk HT-10 pads, and ATE Racing fluid. Those three goodies are, as we’ve seen with other lightweight Mazdas, more than enough for a confidence-inspiring braking system.

Retaining most of the stock brakes is more than enough.

Though dedicated to track driving, this white FD3S RX-7 still wears a set of license plates. His regular attendance at track days and autocrosses in the Los Angeles area generated something of a following on social media, and eventually, Driving Line came calling.

“I wasn’t sure if I could make the event because my car was in pieces when I was approached by Driving Line. I looked at my schedule and saw there was a slim chance if I went without sleep for three weeks, and decided to go for it. I knew I’d have to learn an entirely new setup. Combined with my fear and inexperience with this track, I thought this would be a great growth opportunity for me,” Mac admits. Taking on that level of pressure is commendable — especially when up against a formidable opponent.

GS Werks’ six-point rollcage stiffens the chassis.

The plans were, initially anyway, to put Mac and his RX-7 up against another competitor in an NSX. But, when that driver dropped out, Driving Line brought in a replacement familiar to Turnology readers — but this time with a new car.

Big-Bore Brawler

Skilled, versatile, brave, and very persistent, Steven Kronemberger was the natural replacement. He’s shown his skills on YouTube and made sure to make the Driving Line staff know he was interested. Because he was already familiar with Kronemberger’s driving via internet videos, Mac was thrilled. “When I found out the NSX dropped out and Steve was filling in, I was excited. Not only was I going to meet a great driver I’d been following for a long time, but we were also gonna do battle!”

Kronemberger’s antics in his Honda Civic Type R have impressed many on these pages, and though it’s the fastest car in his stable, he decided to bring another toy to this battle. After a series of eye-opening track days where this Corvette Grand Sport revealed its shortcomings, Kronemberger modified it to suit the circuit.

Though mostly stock, this Corvette Grand Sport has just enough modifications to make the most of an impressive platform.

Unhappy with the car’s excessive body movement, he opted for a set of MCS 2-way coilovers. Helping him charge confidently over crests and bumps where the Corvette does occasionally spin its 325-section NT01s, he enjoys a greater degree of control beyond the limit of adhesion. Considering the speeds and slip angles Kronemberger flirts with, that control is a must.

When the Corvette takes a set, the grip offered by its broad Nittos is immense.

Not Far from Factory

To carry plenty of cornering speeds, Kronemberger replaced the laughable factory seats with a pair of Recaro Pole Positions. With harnesses supported by a Vetteworks Shark Harness bar, he can sit snugly and lean on the Corvette in areas where bravery is more valuable than power.

Girodisc rotors and Hawk pads are more than enough here.

Though the Corvette weighs in at 3,400 pounds with fluids and driver, confidence-inspiring brakes keep him charging hard without fear of fade. His simple setup consists of Hawk DTC 70 pads and Girodisc rotors to help him claw back against lighter, more powerful cars.

In the rear, the 325-section NT01s do a good job of putting the LS3’s approximate 380-wheel-horsepower down, but Kronemberger is always a few centimeters of throttle travel away from a worrying snap of oversteer. With tires that broad, the breakaway is almost always abrupt. Provided Kronemberger treats the rightmost pedal with some caution and commits to the quick corners, he’s able to carry impressive cornering speeds in this big Chevy.

No motor mods: the only aftermarket items in the engine bay are the MCS coilovers.

While it’s heavier and less powerful than the Mazda, it is the stouter package from the factory. And, although it lacks any real aero, its balance, and long-wheelbase help it through the longer corners. With plenty of strengths of its own, it wouldn’t be hopelessly outgunned by the faster-on-paper Mazda.

The Details Make the Difference

Setting these two drivers against one another was perhaps the most complicated part of this challenge. The battle followed a simple format: over the course of several sessions, the drivers strung together a series of quick laps, and their best times were compared. Sounds plain enough, but that didn’t stop both from fretting.

Though Kronemberger slept soundly the night before the event, he had one thing on his mind. “I had installed the MCS coilovers that week, and it was my first time out with that suspension setup, so there was some concern about not having the proper settings for the track,” he describes.

That anxiety was soothed, somewhat, by his familiarity with the course. As the more experienced driver with eight track days before the battle, Kronemberger brought a little more ‘driver mod’ to the fight — something which Mac was comfortable admitting. However, that didn’t mean Mac rolled over.

Despite being a fan of Kronembeger’s, this was the first time Mac (L) spoke with him in person. What a way to meet an admired driver!

Mac spent the prior evening buttoning up a few last-minute issues with the Mazda. Putting the new coilovers on and tying up a few loose ends kept him from getting a full eight hours, but he wanted to bring the best possible version of the car to the competition. For that reason, he saw the event as more of a shakedown. But, after auspiciously besting his personal best time on his second lap, he realized he might have a shot at it after all.

Mac (L) and Kronemberger (R) diffuse some tension with a little pre-battle banter.

“After a few warmup laps, I decided to send it,” Mac laughs. As the lap times continued to drop by seconds with every successive lap, Mac realized upgrading to the new coilovers was a wise choice. “With the new suspension setup, I was able to go flat in places I’d never dreamed of before. I could exit Turn 5 flat, carry that speed over the hill in Turn 6, and floor it over the bumps in Turn 8; there was no section where the car wasn’t totally planted.” Reassurance and improvement in direction changes helped whittle his times down to a 1:31.6 at the end of the timed session.

Kronemberger’s approach was a bit bolder. Kronemberger, confident in his abilities and relieved by his new and surprisingly reassuring suspension setup, was simply more committed in the faster corners at Willow Springs — some of the fastest and least forgiving on the West Coast. His regular slides wowed the bystanders, and his commitment through the daunting Turns 8 and 9 — both covered at triple-digit speeds — was noticeable from the sidelines.

Watching the footage, we witness an evident familiarity with the limit. A mild bobble in Turn 2 (8:01), followed by a rally-style entry to Turn 3 (8:13), shows just how hard he’s pushing. That aggression, complemented by a tidier line and more commitment into Turn 8, ekes out a small lead, as does his gutsy charge through the unforgiving Turn 9.

The Corvette’s body language says it all.

Just listen to his confident stabs at the throttle throughout the final corner, where cojones, tempered by accuracy, make the difference. His characteristically courageous driving and economical line helped Kronemberger cover Willow Springs’ 1.8 miles in an impressive 1:30.5.

Admirably honest, Mac accepted his loss in a dignified way and learned what going up against a quicker driver can do to the ego. Competing against Kronemberger requires some self-confidence — and getting that close to the victor’s time is impressive. At an old-school track with very little runoff, plenty of seat time is needed to carry speed through the corners with the most pucker-factor. Now, with an idea of how hard he needs to push to get the most from his machine, Mac has another goal to shoot for.

Still, everyone left the event cheerfully. The victor was magnanimous at the end of the day. In fact, Kronemberger even helped Mac reassemble his front splitter after an off-track excursion in Turn 3. That camaraderie, diversity of vehicles, and collection of undeniable driving talent are what makes this event such a treat for all involved. The fact these two were found via the internet makes Driving Line’s “Driver Battles” a unique happening.  Let’s hope, for the sake of the future of good-natured grassroots racing, more of these friendly duels make their way to YouTube’s front page.

About the author

Tommy Parry

Tommy Parry has been racing and writing about racing cars for the past seven years. As an automotive enthusiast from a young age, he worked jobs revolving around cars throughout high school, and tried his hand on the race track on his 20th birthday. After winning his first outdoor kart race, Tommy began working as an apprentice mechanic to amateur racers in the Bay Area to sharpen his mechanical understanding. He has worked as a track day instructor and automotive writer since 2012, and continues to race karts, formula cars, sedans, and rally cars in the San Francisco region.
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