carmudgeons.com - View Single Post - What the Mazda RX-8 should have been (new autocross car build)

John V · 10-13-2020, 03:08 PM

I guess when I took a Carmudgeons hiatus I stopped updating this. I'm on vacation this week and relaxing after a hike and a gym workout, so I guess I'll update it for the two people still following along.

This year did not turn out like any of us expected, and even taking CV-19 out of the equation, RX-8 V2.0 did not turn out as expected. I had massive problems with my fresh engine (caused by my new gearbox, which I'll get into) and only just a month ago got everything sorted out.

I'll go in kind of reverse order. This was a month ago down in Virginia Beach at my favorite rolling road with my favorite tuner at the wheel.

It makes 350whp at minimum boost (i.e. on the 7lb wastegate spring) and around 420 at 14psi. We didn't take it higher mostly because I don't think I'll ever need more power than that and more power equals harder to drive. The torque curve is basically flat from 3,000 RPM to redline (it does drop a little bit) and the engine can easily do 550whp, at the expense of longevity. It also makes sweet, sweet noises from the straight cut gears in the NASCAR dog box. Those dog-style engagement rings were the bane of my existence for much of the summer months.

Mazda, in designing the MZR, did what most manufacturers do and went away from keyed timing components. That means the only thing holding the engine in time is friction. That works great when every car is sold with an automatic transmission, or even a synchronized manual. But with dogs, the "gear" engagement is so abrupt it shocks the engine and can throw it out of time. Back in May when I hit the dyno the first time with my fresh engine, that happened pretty much right away. Fortunately, nothing internal was damaged, but the engine and cams being 20 degrees out of time makes for a very poor-running engine. So my freshly-built engine came all the way apart so the crankshaft and timing gear could be sent out to have keyways milled and broached.

Super happy this only took 5 hours, on jack stands even, because at the time the Mazdaspeed3 was on the lift getting all the VVT components replaced and the valves adjusted.

This, combined with the factory friction washers and a crank bolt torqued to around 350ft-lbs should do the trick, and in fact the car ran flawlessly on the dyno.

I also got sick of guessing what my oil pressure and temperature were during competition, so when I found a very inexpensive, used digital dashboard I jumped at it. I think I'll probably 3D print a nicer-looking plate for mounting it at some point, but I needed something quick for the dyno session and so I whipped this up. Including a little circuit to send the fuel level to the ECU. Kinda junky.

Looks okay installed though.

I also put line locks on the car, to make for easier burnouts at ProSolos. Pump the brakes, push and hold the DSC button and release the brakes and voila! The front brakes are locked but the rears are open. Build some revs, engage the clutch, instant burnout.

I've driven the car on the road a bit and think I've found a way to get tags on it. The season was kind of a bust but I'm going to try to get into a semi-local event here before the snow flies.

10-13-2020, 03:08 PM	#349
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	I guess when I took a Carmudgeons hiatus I stopped updating this. I'm on vacation this week and relaxing after a hike and a gym workout, so I guess I'll update it for the two people still following along. This year did not turn out like any of us expected, and even taking CV-19 out of the equation, RX-8 V2.0 did not turn out as expected. I had massive problems with my fresh engine (caused by my new gearbox, which I'll get into) and only just a month ago got everything sorted out. I'll go in kind of reverse order. This was a month ago down in Virginia Beach at my favorite rolling road with my favorite tuner at the wheel. It makes 350whp at minimum boost (i.e. on the 7lb wastegate spring) and around 420 at 14psi. We didn't take it higher mostly because I don't think I'll ever need more power than that and more power equals harder to drive. The torque curve is basically flat from 3,000 RPM to redline (it does drop a little bit) and the engine can easily do 550whp, at the expense of longevity. It also makes sweet, sweet noises from the straight cut gears in the NASCAR dog box. Those dog-style engagement rings were the bane of my existence for much of the summer months. Mazda, in designing the MZR, did what most manufacturers do and went away from keyed timing components. That means the only thing holding the engine in time is friction. That works great when every car is sold with an automatic transmission, or even a synchronized manual. But with dogs, the "gear" engagement is so abrupt it shocks the engine and can throw it out of time. Back in May when I hit the dyno the first time with my fresh engine, that happened pretty much right away. Fortunately, nothing internal was damaged, but the engine and cams being 20 degrees out of time makes for a very poor-running engine. So my freshly-built engine came all the way apart so the crankshaft and timing gear could be sent out to have keyways milled and broached. Super happy this only took 5 hours, on jack stands even, because at the time the Mazdaspeed3 was on the lift getting all the VVT components replaced and the valves adjusted. This, combined with the factory friction washers and a crank bolt torqued to around 350ft-lbs should do the trick, and in fact the car ran flawlessly on the dyno. I also got sick of guessing what my oil pressure and temperature were during competition, so when I found a very inexpensive, used digital dashboard I jumped at it. I think I'll probably 3D print a nicer-looking plate for mounting it at some point, but I needed something quick for the dyno session and so I whipped this up. Including a little circuit to send the fuel level to the ECU. Kinda junky. Looks okay installed though. I also put line locks on the car, to make for easier burnouts at ProSolos. Pump the brakes, push and hold the DSC button and release the brakes and voila! The front brakes are locked but the rears are open. Build some revs, engage the clutch, instant burnout. I've driven the car on the road a bit and think I've found a way to get tags on it. The season was kind of a bust but I'm going to try to get into a semi-local event here before the snow flies.