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2005 Mazda RX-8 - Introducing Project RX-8

Building A Street Touring, Cone-Dodging Machine.

David Pratte
Jul 26, 2010

Project RX-8 With our no-holds-barred S2000 being built for time attack world domination, including some seriously high-end gear like a sequential gearbox and air jacks, we thought it would be appropriate to also explore the more affordable end of the motorsports spectrum with our newest addition to the project car fleet, this Titanium Gray '05 Mazda RX-8. Solo 2 (otherwise known as autocross) is a discipline that requires tremendous driver skill and the ability to properly set up a car be competitive at the national level. But it's also a far more accessible form of motorsport than most because it doesn't require a big budget or much travel on the local or regional level.

Modp_1009_02_o+2005_mazda_rx_8+full_side_view Photo 2/14   |   2005 Mazda RX-8 - Introducing Project RX-8

To prove just how fun and affordable Solo competition really is, we're going to build our RX-8 to Street Touring (STX) specifications and run it at the Solo Nationals in Nebraska in a few months, where more than a thousand like-minded cone-dodgers gather every year for the largest participant-based motorsports event in the world. The beauty of the Street Touring class is that most of the typical street mods are permitted. Upgrades like wider wheels, wider and stickier street tires, coilover suspension and bolt-on power-adders, along with ECU reflashing, are all fair game when building a Street Touring class car.

But to build a truly competitive STX machine requires special attention to detail, whether it be fine-tuning of the suspension and wheel alignment settings or finding creative ways to extract every last ft-lbs of torque from the engine and pull every extra ounce out of the interior (within the rules, of course). So expect to see us go the extra mile with this project, testing every upgrade as thoroughly and scientifically as possible, showing you all the juicy test data along the way.

But before getting down to the fun of STX tuning, first we had to find the right car. In autocross terms, this means the lightest and most affordable model available, so we went in search of a RX-8 Sport model with cloth interior and no sunroof. Most of the used RX-8s we came across were the heavier and more luxurious GT model, but after a few weeks of digging we found our '05 Sport with just 40,000 miles on the clock and a few bonus mods to boot (Mazdaspeed cold-air intake, front bumper and strut bar).

Not that our '05 is perfect. Just as you'd expect, given its age and $12K purchase price, our 8 has many of the common problems associated with '04s and '05s. For starters, it suffers from the rough idle and engine vibration symptoms that suggest the engine mounts are toast, something Mazda has issued a TSB (technical service bulletin) about, so we'll upgrade ours to '06+ engine mounts soon. It also had three factory recalls that the previous owner failed to deal with, so we had our local stealership take care of those (oil cooler lines, fuel tank heat shield and a driveability fix consisting of an ECU reflash and a fresh set of leading side spark plugs). We also replaced the trailing side spark plugs with a pair of really expensive OEM NGKs (these are the only plugs you should use because they're specially designed for the Renesis rotary) so we had fresh plugs all around.

The only thing left to do to our 8 before taking it on its maiden track test voyage was to upgrade its brake pads. At some tracks and for most autocross events, the stock pads or a mild upgrade will suffice. However, at Toronto Motorsports Park where we'll do most of the RX-8's testing, there are several very heavy braking zones that require a heavy-duty brake pad that can take the heat. For this we opted for Hawk Performance HP+ street/track pads up front and the slightly less aggressive but still very capable HPS pads on the rear. The RX-8 has huge brakes from the factory, but having experienced severe brake fade at this track before, we weren't going to take any chances.

With the pads installed and bedded in the night before, we loaded our STX wheel and tire package of choice into the back seat of the RX: 18x9-inch Volk Racing G2 flat-black forged wheels and 265/35R18 Bridgestone RE-11 extreme performance tires. Weight is the enemy in any form of motorsport, especially when it comes to wheels and tires (the whole unsprung and rotating mass thing), so we searched high and low for the lightest and stiffest wheel money could buy in a 18x9-inch size along with the stickiest 140 UTQG 265/35R18 tire (these being the maximum rim and tire width permitted in STX for a RWD car). What we came up with is admittedly a little more baller than what some budget-limited autocrossers might choose, but if you're going to break the bank at any point during a project, wheels and tires are by far the best places to do it (and you'll see why in just a second).

After doing a few warm-up laps on the factory wheels and OE-size Toyo T1R tires to get a feel for the car, we adjusted tire pressures based on the tire temperature readings we measured across each tire's contact patch. We then did a three-lap session with a best lap time of 1:29.66. This lap time was slower than we were anticipating, but our RX-8 seemed to have a lot of understeer when initiating turn-in, perhaps because of the fairly narrow OE tire size.

We then swapped on the VR.G2 wheels and Bridgestone tires and repeated this process, first doing a warm-up session so we could dial in tire pressure based on the tire temp data we collected with Enmo Racing's Longacre probe-type digital pyrometer. We then banged off four clean laps in the 1:26s, a full 3 seconds quicker than the OE wheel and tire setup. Feeling like there was still a bit more time out there, we reset our tire pressures to 39 psi front and 37 psi rear (hot pressures) and made one more three-lap run for glory. On the first lap we posted a 1:25.82, almost 4 seconds quicker than our best OE time and on the second lap traffic ruined what surely would have been a low 1:25.00. Impressive improvement, to say the least!

According to Eddie Lee from Mackin Industries, one of the leading wheel experts in the industry, "Volk Racing forged wheels like the VR.G2 provide higher camber stiffness, which really allows the tires and suspension to do their job." We also value the fact that these wheels are extremely lightweight and durable, making them a perfect fit for a street/track build like our RX-8 that needs a wheel that can survive pothole strikes on the street and curb strikes around the track. Wheels this sexy should also help us avoid striking out with the ladies, although our McLovin fake ID should help, too.

Obviously, a wider and stickier tire also helps a lot, a fact we covered in some detail in last month's Tire Review of the RE-11s. As we stated in that review, the understeer present with the OE wheel and tire setup was replaced by crisp turn-in response and impressive mid-corner grip after we bolted up our STX wheel and tire package. This translated into much higher corner exit speeds and resulted in higher top speeds down the straights. The RE-11s also provided a lot of useful feedback as we approached their limit of adhesion, making it easy to tell when too much speed was being carried into a corner. And when we did overcook a corner, oversteer was always gradual and predictable, so recovering from a slide was fun and easy.

Next we'll be bolting up a set of BC Racing coilovers to see what sort of time we can knock off our best lap at the test track, plus we've got a road trip planned to test out our suspension settings at the Seneca Lake, New York, Solo National Tour event. Come join us at this event if you live in the area!

By David Pratte
216 Articles

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