It’s no secret that tires play a huge role when it comes to performance, both on and off the track. We’ve come a long way with Project RX-8 during its track development, having knocked 6 seconds off its stock lap time so far. A byproduct of all this track development has been a worn-out set of Bridgestone RE-11 tires, a sticky set of summer rubber we originally opted for because we were targeting Solo 2 STX class as the car’s competition playground.
Sadly, we never made it out to an SCCA Solo event, and since we’ve rebuilt the engine with a whole host of lighter and stronger components, it’s no longer STX legal. So instead we’ve decided to have some Time Attack fun with our Mazda, despite this type of competition normally requiring big horsepower. To hang with the turbocharged and V8-powered cars in CSCS’ Super Street RWD class (between Street and Unlimited), we’d have to take the fight to them in the braking zones and around the corners, meaning we’d need the stickiest rubber we could legally run. But before that, we’d also have to get oil temps under control a bit more because the new engine is making some serious heat.
During the 8’s maiden voyage around the racetrack with the new and improved engine, we went 1 second a lap quicker than before (thanks to about a 40-whp gain), but we were also seeing oil temps in the 240-250-F range, and that’s getting a little too hot for our liking. To address this, we’ve gone the DIY route by opening up the venting on the exit side of the twin front oil coolers. For this all we did was take our FatMax box cutter and open up the exiting vents in the front wheelwell liners and add one to the top row. It’s literally a five-minute job per side if you leave the liners on the car while modifying them, and we did see a 10-degree drop in oil temp as a result. Free mod that works = #winning!
We also noticed quite a bit of oily buildup in the throttle-body and upper intake manifold during the rebuild, so another very simple mod was in order before attacking time. We’ve used everything from a Gatorade bottle to an aluminum water bottle with some steel wool stuffed inside it as an oil catch can (to separate oily vapors that are normally vented directly back into the intake in front of the throttle-body), but that wouldn’t look right anywhere near Project 8’s blingin’ Mazdaspeed strut tower brace with Moton canisters. So to dress for success, we ordered up the well-crafted Mishimoto carbon-fiber catch can kit, which comes complete with all the fittings and hose required for the installation. This, too, is a quick and easy installation, especially if you forego fabricating a proper mounting bracket and instead zip-tie it to the fuse box housing like we did. That’s right, we ghetto-installed a high-end catch can, but so far it’s working perfectly and looks totally at home in the engine bay.
As for that sticky rubber, Super Street/Limited class specifies a treadwear or UTQG rating above 40, which makes Hankook’s new Ventus TD semislick (80 UTQG) an ideal choice. Based on the very promising results a few top drivers have had on this tire already, we were certainly hoping the soft compound (C70) Ventus TDs we ordered in a 265/35R18 would give our 8 the grip needed for a podium finish. But we also needed a lightweight set of wheels to mount them on.
For that we turned to TSW, a wheel manufacturer with a 30-year history in motorsports founded by a former F1 driver and having produced wheels that have survived the grueling 24 Hours of Le Mans. These days, TSW is best known for its huge array of one-piece, staggered-offset wheel fitments, but for us hard-core go-fast types, TSW recently added two lightweight forged wheels to its lineup: the Nürburgring RF and the Interlagos RF.
The RF here stands for rotary forged, a forging process in which the barrel of the wheel is formed at high pressure while the wheel is being spun at high speeds. As Terence Scheckter, president of TSW Alloy Wheels, told us, “This process greatly enhances the strength of the wheel and reduces the weight. Most importantly, the rotary forging reduces the weight in the most critical part of the wheel—the barrel—and thus improves acceleration and braking.”
Given the low torque production of our naturally aspirated Renesis, reducing rotating and unsprung mass is even more important, making the 18.3-pound weight of TSW’s 18x9-inch Interlagos RF especially attractive. And to put these wheels into proper context, the Interlagos RFs are not only among the lightest 18x9-inch wheels on the market today, but they also sell for right around $1,000 for the set of four, making them incredibly affordable, too. As a result, they’re accessible not only to professional racing teams but also to grassroots enthusiasts like you and me.
We also love the way these TSWs look on our RX-8. The +32 offset provides an aggressive track width without any concerns over fender rub, and as an added bonus, the mirror-cut finish sheds brake pad dust extremely well. Sometimes you really can have your cake and eat it too, and thanks to TSW, we’re enjoying all the benefits of a lightweight forged wheel without maxing out the credit card.
With the Hankooks mounted up and the directional tread facing the right way, it was time to get the RX-8’s setup dialed in for maximum grip and cornering balance. Starting with tire pressure of 35 psi on all four corners, a few laps later we took hot tire temperatures using a probe-type pyrometer. We thought perhaps the soft compound TD would reach optimum operating temperature (around 180 F) in a lap or two, but somewhat to our surprise, we only saw temps in the 140s. Nevertheless, the grip level was already very impressive, with lap times dropping into the mid-1:21 range (compared with our best street tire times in the high 1:23s).
Given the cool ambient and track temps, we bumped the pressures to 40 psi front and 38 psi rear so the tires would build heat faster. Sure enough, after a three-lap session, we were seeing tire temps in the 170-190-F range, just like we wanted. But the car was now suffering from turn-in and power-on understeer, so our lap times didn’t improve from the first session. To address this handling imbalance we bumped up the rear tire pressures and stiffened the rear Moton Clubsport dampers one position on both the compression and rebound adjusters. If you’ve ever used Motons then you know even a one-click change has a big effect.
With testing complete and the CSCS Time Attack session about to start, we took one click out of the rear rebound settings because the car was a bit loose after our previous adjustments, but we left tire pressure alone because the temp readings were now pretty much spot on. The RX-8 felt nicely balanced during the three-lap TA session, and with a best lap of 1:20.7, our adjustments moved things in the right direction. Unfortunately it wasn’t enough to beat the C5 Z06 or E90 M3 in our class, so we finished in Third Place in a 13-car class.
This lap time represents a new best for Project RX-8, and we only plan on going faster with the addition of some functional aerodynamic upgrades as well as shorter gearing, greater camber adjustability, and maybe even MOAR PWR!!!! We have another CSCS Time Attack coming up next month, which means we don’t have much time to get some of these mods on the car. Time to get wrenching.