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Old 01-07-2018, 12:20 PM   #1
John V
No more BMWs
 
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Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
What the Mazda RX-8 should have been (new autocross car build)

I'm not 100% sure where this is going to go yet, but for the two or three of you that are interested I'll take a crack at documenting the work to get this thing together.

First of all, I have an irrational love of the rotary engine. I blame Car and Driver. In 1992, they broke the story of the upcoming FD-chassis 3rd gen RX-7, and by all appearances that was going to be a landmark car both for Mazda and for sports car enthusiasts. Given that I was 14 when that magazine landed in my mailbox, I had nary a hope of getting into a third gen anytime soon. But that article also had a little blurb on the second-gen RX-7 and while I had seen these cars on the road I knew next to nothing about them (okay, I knew next to nothing about cars beyond 0-60 times, skidpad g's and braking distances). When I landed a second gen turbo as my first car two years later, I was immediately a member of the Wankel-engine fanclub. That car taught me more than I ever expected about the love and frustration of working on cars.

Fast forward to 2004 and our very own Clyde offered me a ride in his first-year RX-8 at a local autocross. I had actually intended on buying the RX-8 when I got my first real job out of school in 2002, but delay after delay meant I had to postpone that goal, and I took the opportunity to buy one of my other high school dream cars, an E36 M3. I loved the M3, and to be honest my interest in the RX-8 had long-since waned, after the "scandal" of Mazda over-rating the RX-8's naturally aspirated rotary hit the press.

But hopping into that car was a revelation. It turns! It stops! It'll even do both at the same time! The wonders of a low center of gravity, the stiffest chassis on the market, double wishbones with great geometry. I was pretty torn. Clyde and I drove that car together for a few years and I've never forgotten the fun we had. I also never forgot just how phenomenal the chassis was and just how underwhelming the engine was.

I couldn't quite shake the thought of getting one as a street car and putting a real engine in it. LS V8? Seems like a great idea on paper, but it's been done and I'm not sure the character of the engine fits the car. Maybe something that revs a bit faster and puts a little less weight on the nose (mostly it's the weight of the beefy transmission that needs to go behind an LS, but either way it's weight). I had also thought for years about doing an autocross car using an RX-8 as a starting platform. There is one class that seemed to make perfect sense: Street Modified.

For those not familiar with SCCA Solo classing (basically everyone on the planet?) Street Modified is a class for four seat cars where the drivetrain is essentially free. The class was based around one rule: Make as much power as you want, using an engine made by the manufacturer of the chassis. i.e., Mazda power in a Mazda. The rule set obviously consists of more than that, but that's the basic premise. So my first thought two or three years ago was why not drop in a 3rd-gen RX-7 13B? The formula for making (relatively) reliable power (in the 450hp range is generally understood to be required for competitiveness) is known using the 13B-REW. There are kits to get the engine to bolt up to the RX-8 and it would be relatively straightforward to build.

But I got to reading the rulebook and was reminded that in SM, there is a minimum competition weight that is based on drive configuration, induction type and engine type. Long story short, a 13B turbo rotary has to weigh at least 2,700lbs. The same car with a 2.5L four cylinder turbo piston engine can weigh 120lbs less. On top of that, 13B-REW parts are pretty expensive and reliable tuning on a rotary is challenging. My mind was made up. I went hunting for an RX-8.
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