JDM Giants: Comparing A Supra And RX-7 On Road And Track

Over the last decade, Martin’s been able to thoroughly enjoy two of Japan’s most-respected sports cars. These two are similar in some respects; flowing lines, curvaceous bodies, intriguing powerplants, and rear-drive layouts distinguish them and put them on a slightly higher pedestal than other contemporary cars from that country. Since the Toyota Supra Turbo and the Mazda RX-7 have cultivated massive followings, their prices have skyrocketed over the years and many of them are condemned to a lifetime spent in a climate-controlled garage.

Fortunately, Martin isn’t someone who worries about such things, and through lots of tuning, trips to the Nürburgring, and plenty of backroad blitzes, he’s been able to understand the peculiar characters of these two — warts and all.

The fourth-generation Supra leads something of a tortured life. Stateside, it’s most frequently used as a highway dragster, or worse, it’s kept untouched in a garage; it’s one of the few Japanese cars which has risen to the status of “collectible.” Few of them make it to the road course, and in some part, this is understandable. Toyota over-engineered this machine, and as a result, created a heavyset grand tourer better suited to long-distance tours — or so some think.

Martin had little difficulty taking the comforting Supra 400 miles to the Nürburgring several times.

Strong Additions to the Footwork Department

Martin made strides towards a track car, but rather than strip it of all its comfort, he made a series of intelligent modifications to better enjoy it when the public road grew twistier. For instance, despite running the car on stiffer shocks, he retained the stock bushings to retain some level of civility on the street. Intelligently, he aligned the Supra for fast roads, not for road courses with the greater demand for camber. This setup made for stability over bumps, minimal tram-lining, and a level of composure that would give him the confidence to push, regardless of the surface.

Of course, better poise was an objective, so he shod the 17-inch UK-spec wheels with Pirelli P Zero Corsa tires — a 245 section in front and 275 section in the rear. Underneath, he fitted the larger UK-spec brakes — four pistons in front and two pistons in the rear. Chris Wilson pads (similar to a Ferodo DS2500) and Goodridge braided brake lines gave him a little more confidence in bringing the 3,300-pound Supra to a stop. 

Bilstein Yellow dampers provided a compromise between a compliant ride and reassuring body control at speed, and Whiteline swaybars front and rear offer a stable platform. To sharpen the Supra’s steering, which is often criticized for being dull, Martin added some caster and converted to the TRL speedometer, which sends the correct signal to the ECU to make the speed-sensitive rack work properly.

This compromised approach meant the car excelled at the Nürburgring, where it was compliant enough to handle the cambered, pockmarked surface — much like that of many country roads. A long wheelbase adds to the Supra’s stability at speed, its stability under braking, and its tendency to mildly understeer with neutral throttle input never left him intimidated.

“Brilliant fast road car; the suspension was perfect. Little soft on track, but at the Nürburgring, it didn’t feel out of place,” summarizes Martin. This benign character always inspired Martin to push it hard, and provided he avoided excessive throttle, it was always reassuring, predictable, and manageable — ideal traits for a fast road car. With some practice, Martin was able to snag an 8:21 lap at the Nürburgring on a mid-boost setting of 16 pounds. 

The Famous Powerplant

Without making a few modifications to the motor, Martin wouldn’t be taking full advantage of the wonderful powerplant. He left the 2JZ-GTE mostly stock, but a few tweaks yielded 434hp at the rear wheels with only 14.5 pounds of boost.

All that was required were a set of Denso Iridium IK24 spark plugs, GReddy front-mount intercooler with a hard-pipe kit, a Blitz Nur Spec Exhaust, and a Chris Wilson double de-cat. As far as electronics went, he mounted an Apexi AVC-R discreetly in the head lining, and added a TRL Fuel Cut Defender to raise the boost pressure safely. 

Keeping the powerplant cool was a concern, so Martin opted for ERL water-injection system, as well as a UK-spec hood with a scoop and internal ducting. Lastly, he toughened up the drivetrain with an RPS Street clutch. The sequential turbocharger setup offered plenty of torque across the rev range, making it usable in most conditions. However, its few flaws were noticeable.

The only issue was the violent turbo changeover with a factory sequential setup. “Virtually all the additional power to the curve came online at 4000 rpm; roughly a 100-hp climb within a 500-rpm window, which made it a handful in the wet,” recounts Martin. 

“In the dry, it was actually quite good fun. I learned to sense the power coming in and often straightened the steering in anticipation of the rear stepping out,” he notes. Turbo lag wasn’t obvious by feel, but a rolling drag with his friend’s F355 made a very mild delay obvious. Once the boost came in, Martin had no difficulty showing his friend the broad rear haunches and those unmistakable taillights.

Over a number of trips to the ‘Ring, Martin was able to whittle his laptimes down to a respectable 8:21.

As usable and potent as the 2JZ was, its packaging did hinder the driving dynamics in some ways. The iron motor is heavy, long, and tall. Additionally, the turbocharged power wasn’t always delivered as precisely as he would have liked, and the 2JZ had a heavy dual-mass flywheel to counter transmission rattle at idle, making it slightly sluggish at times. “I still have fond memories of the power delivery and sound though,” says Martin.

For a snug fit at speed, Martin went with Recaro Speed SR seats. A MOMO steering wheel compliments that angled dash which envelopes the driver making them feel like a fighter pilot. With the center console and door cards partially retrimmed in Alcantara, the cabin felt a little more focused, but still far from a stripped interior of a track toy. An Alpine head unit, upgraded speakers, and concern for the aesthetics made it a cushy place to be when cruising across Europe.

For years, Martin made frequent trips to the Nürburgring. However, a 130-mph blowout gave him pause. A sober period of reflection, this made Martin all the more cognizant of the Supra’s foibles, and he began to seek a machine with sharper edges. Instead of going the Porsche route like so many track addicts do, Martin replaced the Supra with a sharper-edged machine which was one of the Supra’s direct competitors in its heyday.

Shifting Focus to a Svelte Fighter

The Mazda RX-7 is still universally renowned for its handling prowess. Lighter, smaller, and better balanced, the third-generation RX-7 is an adept corner carver with all the traits a track car ought to have. In this comparison, some might consider its weak point to be the temperamental 13B-REW engine. Martin is part of that group, so he swapped it for a recognizable powerplant from across the pond. Best of all, this new setup retained the car’s wonderful balance, and sidestepped the turbocharging issues.

With similarly smooth, organic lines, the RX-7 could be the Supra’s slimmer brother.

When implanted in the bay of an RX-7, the Chevrolet LS3 is known to infuriate purists. However, the long list of perks makes it hard to argue with. This particular mill was pulled from a 2010 Camaro, complete with a Tremec TR6060 six-speed, which sends power to a Cobra rearend with the 3.55 final drive. Thanks to the abundance of swap kits available, shoehorning a V8 in the Mazda’s bay wasn’t a chore. With Samberg subframes and radiator, there was still enough room in the bay for air-conditioning, an LS1 Corvette fuel-pressure regulator, and a Supra Denso fuel pump.

Obviously, power and torque make it appealing. The Camaro-spec LS3 left the factory with 424hp and 420 lb-ft of torque. The LS3 also offers instant response with the Fidanza aluminum flywheel, and the power delivery is progressive.

With such an understated appearance, the LS3 could pass for stock.

With this powerful, normally-aspirated engine replacing the Mazda’s finicky rotary, the Mazda can now compete with the Supra in terms of straight-line speed. In fact, the V8-swapped RX-7 even outguns the Supra in the high-speed sections of the ‘Ring; snagging 170 mph under the Gantry. It’s hard to dislike that combination of reliability, packaging, and power.

Sharper and Stiffer

Despite the world-class powerplant sitting in the bay, the agility of Martin’s Mazda is still its strongest point. To capitalize on that, he installed a set of Ohlins DFV coilovers with plenty of spring rate and a good amount of camber. Recaro Pole Position kevlar seats keep him planted in the middle of a quick corner, though without a cage, he can’t add harnesses, which would offer the ideal level of support.

The Mazda’s suspension is quite similar to that in the Supra, but much lighter with more aluminum components and an independent-rear toe and camber mechanism. The front lower wishbones are in a different league in terms of weight, as they are made from alloy rather than steel. That’s likely where the majority of the money was spent; the rest of the car is second best to the Supra. For instance, the Mazda’s windshield wipers would completely stall on the window at 140 mph and slow down above 100. Martin eventually used two relays to provide direct battery feed, instead of going halfway around the car through the switch gear, but that ingenuity still cannot compare with the Supra’s remarkable build quality. 

If it wasn’t already clear, Martin made this car more suited to the demands of the track. The addition of Stoptech 332 x 32mm big brakes with larger pistons and RS/RZ 314mm rear Mazda brakes, fitted with Carbotech XP10 pads front and rear, give the car the sort of deceleration a track-oriented car needs. A Setrab power-steering cooler, and a single Setrab 25-row oil cooler are other additions made to help the car handle the abuses seen during hard driving, and a rear-mounted Odyssey ER40 battery improves weight distribution. Clearly, he was not building this car for cross-continental trips like he had the Supra.

An Advantage in Agility

Thanks to the shorter wheelbase and the centralized mass, the Mazda feels more nervous at speed. Simply put, it’s less forgiving and requires a little more concentration. Though the steering ratio is the same as the Supra, its dimensions put it on a relative knife edge, and at first, it would rotate with the smallest tweak of steering or throttle. The one downside to having so much displacement, and a relatively short throttle travel, is the tendency to overwhelm the rear tires in slower corners. In the faster corners, the weight transfer happens quite quickly, and if not managed carefully, the RX-7 can bite.

At 3:53, we can witness its vicious side. After lifting for an extended period of time, the weight transfer encourages the rear to rotate quite abruptly. Though he tries to catch the initial slide with a flick of the steering wheel, the window between sliding and spinning is narrow, so Martin is soon off into the grass. Fortunately, this one spin through the Craner Curves allowed him to walk away without damage, and showed him exactly how vital maintenance throttle and accurate steering is, with such an agile machine.

Understandably, Martin struggled to transition to this new level of incisiveness on track. “The car responds so quickly to steering input that the initial thought is the rear is going to let go,” he warns. To stabilize the rear, he eventually added some rear toe in, which gave him some needed confidence when pushing the car hard.

To make the edgy RX-7 somewhat more agreeable, he made a few changes to its rearend. At first, the LS3 sent power to a 2004 Mustang Cobra limited-slip differential, which generated a lot of heat and blew oil out of the breather. After three track days, the plates were on their last legs. So, he switched to a Torsen T2R differential which reduced heat and engaged much more smoothly. 

A sturdy rear helps deploy the American grunt over the Nürburgring’s undulations.

The Price of Precision

Unfortunately, the price paid for this seamless driver-car connection is a certain degree of harshness, which the Supra never shared. There are several points which stand out. First, the Mazda’s rear subframe is solidly mounted to the body as standard. Second, the engine vibration and noise does define some of the driving experience — while it’s bearable on the road, it keeps long trips from ever being described as luxurious. 

Though it’s not as bad as some of his friend’s stripped track cars, the interior is very snug and can get quite warm. To keep the interior from becoming a complete sweat lodge, Martin fitted 3mm reflective DEI tunnel shield to the bulkhead and tunnel externally, then used closed-cell foam on the interior of the floor and tunnel. He also fitted air-conditioning for longer trips, which are bearable, but not quite as cushy as those he took in the Supra.

Once the tires are warm, the Mazda delivers its power much more effectively. Even in first gear, Martin says it generally leaves the line without much wheelspin. Here the RX-7 has the edge on the Supra as the weight distribution is slightly more rear-biased.

The linear power delivery is predictable, but tTo keep himself out of the ditch, Martin fitted Racelogic traction control. “If I need to make progress in the wet, I turn the slip down, but generally run it at +20-percent slip, which allows liberal power slides with hardly any intervention,” he adds gleefully. 

In short, the Mazda is the smaller, more track-focused drivers weapon, which performs with greater precision and feedback, and feels like it was meant for cornering. In contrast, the Supra isn’t quite as single-minded as the RX-7, but with the right modifications has more than enough to impress on tracks and backroads alike. However, there’s no getting away from the extra girth; the Supra used to feel quite big on some twisty country roads, where the Mazda, thanks to its shorter overhangs and slimmer figure, is much easier to place on the road.

The Supra, a cosseting cruiser, isn’t completely able to defy its greater mass. That said, the plentiful cabin space, strong torque, and benign character near the limit of grip encourage the driver to push. It’s not quite the incisive scalpel that the RX-7 is, but it also isn’t quite as draining to drive and works well in a variety of conditions. Clearly, both cars can be made to work well on track and on the public road, but hopefully, this comparison shows that the effects of mass are ultimately unavoidable, and any dual-purposed car — whether it be a streetable-track toy, or a sharpened road car — will be compromised in some significant sense.

Despite being the rougher, rawer machine, the RX-7 still served Martin well on a trip through the Alps.

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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