Help me choose RX8 transmission gears

I am playing.

I have two choices for my transmission, and I can't decide which I like better.

The first choice is a stock 6 spd. 3.76/ 2.269/ 1.645/ 1.187/ 1/ 0.843.

The second choice is a cobbled together 5 spd made of pieces from an RX7 turbo and an RX8 tailpiece. 3.484/ 2.015/ 1.391/ 1/ 0.762.

I will be using this car for the $2016 Challenge- autocross and drag racing. I have no need for an overdrive, and don't care about fuel economy.

Car is about 300 lbs under stock, has a lightened flywheel, and MAY have nitrous.

It's got a 4.44 rear end, and will be rolling on 315/35's.

The tighter stock ratio should give me more shifting choices, but the 5 spd may force my shifts higher into the meat of the rev range, and eliminate 1 shift on the drags.

Thoughts?

Lots of factors here... generally, shorter gears are better for performance.

In reply to NordicSaab:

Right, but in this case that means the RX8, and my concern is that the gears are so short (for fuel economy and cruising rpm's) that they encourage short-shifting. The RX8 LIKES to run at 8000 rpm.

which 6 speed is it?

Another factor: My understanding is the R-type is a lot sturdier than the Aisin in the RX-8. If you're planning to run a stock engine it might make sense to stick with the RX-8 transmission for the additional gears/closer ratios. If you're going to run sticky tires with a considerable shot of nitrous it might make sense to go with the R-Type.

oldeskewltoy wrote: which 6 speed is it?

Stock 1st gen RX8

My assumption is the Mazda Engineers spent more time than you and I ever will deciding on gear ratios based upon factors known and unknown to us. I would leave the stock (shorter) transmission gears in place.

Also, don't rotary engines(apex seals) strongly dislike lower RPMs with (higher) load? I ask because that would be a common condition you induce with longer gears.

SVreX wrote:

oldeskewltoy wrote: which 6 speed is it?

Stock 1st gen RX8

should be AZ6 then......

ratios from other AZ6 equipped cars....

S15 6 spd 3.626 2.200 1.541 1.213 1.000 0.767

NISMO 2.907 1.989 1.537 1.218 1.000 0.862

RX8 6 spd 3.760 2.269 1.645 1.187 1.000 0.843

Miata 6-spd 99- 3.760 2.269 1.645 1.257 1.000 0.843

SXE10 6 sp 3.874 2.175 1.484 1.223 1.000 0.869

TRD(33030-SE100) 3.106 2.175 1.585 1.223 1.000 0.869

The only interchangeable gear would be the 6th gear. It is possible to swap in the Nissan 6th gear into other AZ6 variants. From what I've heard, you can't mix gears.... but since the basic architecture is the same, you may be able to swap entire gear sets.

This originally came up because when I bought the car it was believed to have a bad transmission, and I had a free RX7 trans here I was going to modify.

Turns out, the trans is not bad- just the clutch throw out bearing.

So, while it is out of the car, I was debating whether there is any advantage to going back to the old plan.

Clearly, Mazda engineers are better at this than me. But they were building the car for a lot more parameters- fuel economy, highway cruising, comfort, top end speed, etc. Things I don't really care about.

I know what I'd do in a car I was more familiar with, but I know nothing about rotaries or RX8's. Figured it was worth asking.

Is the other transmission a bolt in job or will there be fabrication to put it in?

Both are bolt-ins.

Are you increasing the power output at all?

If your putting out a decent chunk of power above stock then it wouldn't hurt to go the turbo ii box. Otherwise if Power is staying close to stock, that extra gear below 1:1 may just come in handy.

Im pretty sure the turbo ii had a 4.1:1 diff ratio, so the 4.4 in the rx8 would make the turbo ii box feel a bit shorter than it was in the turbo ii, Wich isn't necessarily a bad thing.

Don't suppose you've been able to figure out bellhousing interchangeability between the two boxes yet?

At this point, the only power output increase will be the nitrous.

Bell housings are identical.

You're only using the nos for the drags yeah? If so probably just keep the rx8 box so its not to spread out for the autocross.

Identical to the engine? Or to the box? Or completely identical?

In reply to daeman:

Identical to the engine, I have not checked to the box (but I think they are identical).

The main difference is the tailpiece to accommodate the PPL.