I would contact the regulating authority and seek clarification on the calculation ....... that's way too harsh on a rotary at 3.108L !

No, those are the rules and have been since forever. I just had a total brainf@rt is all.

I assume you're talking about a one rotor engine based on 13B parts? But the way you notated "(654/2)*2)" doesn't make sense. The weight formula for a one-rotor using 13B parts would be more accurately represented by:

0.9 + 0.654 + 1.4 = 2.954L.

I suppose you could do that, but I don't see it spooling an appropriately sized turbo in a way that is remotely usable for autocross. Also, I don't see a legal SM RX-8 getting below 2500lbs with an engine making enough power to be competitive. I could be wrong, but I don't think it's possible.

I think the weight formula for rotaries is reasonable in SM. IMO the rules should be written to encourage builds that don't require extreme costs to put together, so more exotic stuff should be penalized with more weight. In the grand scheme of things, a 13B turbo needing to weigh 120-ish lbs more than a 2.5L turbo 4 is not that big of a deal, especially when you consider the rotary should spool faster (much more exhaust heat) and should have a lower Cg and polar moment of inertia.

Where the weight formulas really fall apart is with big displacement (cheap) engines. An RX-8 with a naturally aspirated 5.3L LS should be able to make the same low RPM power as my car but it'll be harder to make the same power up top. And yet it has to weigh over 3,000lbs. Makes no sense.

A number divided by itself is always 1. You didn’t have to divide total 2-rotor displacement by 2 and then multiply by 2 in your formula, which made no sense to me either.

the turbo exists and is readily available. The output goal is no issue, even understated. As you noted, the target weight is the issue. In my estimation 2300 lbs might be possible. Lighter, less torque with more rpms, creates a situation where heavy HD components are not as necessary. Just a pipe dream though ...

I called out the displacement per rotor as 1308 divided by two because most of us recognize the rated displacement of a 13B as 1308.

654/2 is meaningless.

I believe you can get enough power with one rotor to be competitive. I believe it will absolutely suck to drive.

:lol: you crack me up man, you still don’t recognize I copied your formula and just plugged the numbers in. I didn’t bother changing it because I know it’s .654L/rotor, but more importantly; *it doesn’t matter* and editing posts on my phone is a pain. I boffed up the formula previously though and can appreciate that you now think I’m that dumb. :) That’s on me, but how about we spare everyone else and not add a page or two nitpicking each other apart over pointless minutia up until there’s a blowout, ok?

I also won’t bog your thread down any further over the alternative engine scenarios. Thanks for assisting me with the original question.

Sounds like you need a better phone :lol:

I don't think you're dumb. But I was really struggling trying to understand how you were creating a two rotor engine that was exactly half the displacement of a 13B. :lol: It's all good though.

I saw what Team did in post #209 as well and was like ...wtf ?
That was 2 brain farts in quick succession Team !

Yes, because taking total displacement, dividing by 2, and then multiplying by 2 makes so much more sense. :slap:

Enjoying the thread, really nice car .
​​​​​100% agree with your reasons for not doing a 13b.
​​​Love the engine, hate the cost. It's unfortunate the bang for the buck has faded so much.

.


Or just do the same thing with this slightly modified and bolted to a top plate instead :suspect:


https://cimg5.ibsrv.net/gimg/www.rx8...575263c9a.jpeg

Guess I never updated this. Oops

I had to redesign the transmission crossmember to accommodate a GM-style gearbox mount which is used on the G-force. Yay fun

https://lh3.googleusercontent.com/JM...=w1036-h777-no

Fits like a glove.

https://lh3.googleusercontent.com/EE...A=w583-h777-no

ABS now lives behind the driver's seat and all lines were removed and remade using PTFE AN fittings.

https://lh3.googleusercontent.com/kA...=w1036-h777-no

The G Force gearbox swap created a ripple effect of changes. I needed to stand the engine straight up to accommodate it, and that meant the ABS pump needed to move since it was where the inlet plenum's path. The easiest spot was behind the driver's seat. I also relocated the remote oil filter and cleaned up some of the crankcase ventilation and catch cans. This gave me room to move the ECU and make some brackets to hold the shock canisters. It's a lot easier to work under the hood now. Next up is deleting the stupid prop rod, and I guess I should continue gutting the underside of the hood to get the last pound of weight out of it.

https://lh3.googleusercontent.com/iF...=w1036-h777-no

nice work. looks like you the sumitomo abs unit. that's the prefer abs over the bosch one from what i'm told by a veteran scca road course racer.

It came with the car, since it's a non-DSC base model from '05. I can confirm it works extremely well.

First time driving the car with the new gearbox. Seems like it's running great, and it's going back on the dyno on Saturday to run in the motor and update the tune for speed/density.

better take it to the dealer for that CEL :suspect:

lol

Look again though, no CEL.

steering?

Yep

Back on the dyno, with fun dog box noises. The car ran flawlessly for the 30 or so runs we did dialing in the cams, transient throttle, and various levels of boost.

Great progress!

Stock belt tensioner or a manual one?

Stock sprung tensioner

what tension? lol

It's actually very tight. But it's a long gap between the tensioner (on the cylinder head) and the crank pulley.