RX8 6 speed in FC
 

Ok Hers the plan. I can get a steal on a new RX8 transmission. A friend of mine tells me that with my current TII drivetrain setup (bolted to a '89 N/A) the transmission will bolt right up to the TII flywheel etc. Now of course I'll need a custom crossmember , RX8 slave cylinder, and shifter assembly. THe whole escapade will cost me roughly $1200 compared to the $700 price to rebuild my TII transmission (with custom modifications). Now my question is will the swap be worth it? I'll have closer gears and the 3.90 auto rear is going to be replaced with a TII rear with 4.30 ring and pinion. Any thoughts on this subject?

closer gear ratios do improve acceleration somewhat, sounds quite interesting though, just one question: is the rx8 tranny as strong or stronger than the TII tranny? i mean if later on you decide to swap to a TII engine or 13rew or whatever.

What about the bell housing and the driveshaft will they be custom made or what? Also will the RX-8 shifter line up with the FC's shifter hole?

Thats a really good question. The engine does sit lower than the regular rotarys, but its still a 13B with the same displacement, honestly I think the bell housing will be the same size as the other trannys. What might not work, is the bolt pattern, as im sure they are different, maybe you need an adapter plate?


Where are you buying the 8 tranny btw?

How much is it through the dealer?


Strength, like the other guy was saying, I don't know. But it supports the 5psi kit from greddy, so obviously the tranny is much better than the NA one.

Damn, if this works, I might look into this down the road

it sucks to be referred to as: "the other guy" lol

i read that mazda kept the rotary bellhousing and bolt pattern but i forgot where i read that. i think a 6th gear would be awesome, also the rx8 trans is made for 10,000 rpms so it might be more well balanced or something like that, but isn't the rx8 driveshaft aluminum or carbon fiber or something crap? the rx8 sure is beatiful.

well about the strenght thing..... they have to be strong concidering they come with more hp than a t2......... there is a guy running a 500 hp 3-rotor rx8 w/ the stock 6-speed... so im sure it can handle the power!! :)

im almost certain they retained the same bellhousing pattern.... but you'll need the rx8 starter (might be different), slave cylinder, a custom driveshaft, and all the shifter mumbo-jumbo....

the big question is......... will it line up with the shifter hole of a fc........ ill have to measure speeddemons rx8 and see if they are the same

Well the trans has already been measured. Its the exact same length. Also the shifter will only be off by about 1/2 inch. It will bolt directly up to the engine and the starter will even fit. AS long as TII drive train parts are being used it will work apparantly. AS far as strength goes I don't know. My friend rebuilt it and said that the input shaft and amongst other parts were just as big as the FD's. I'll have to fabricate a crossmember and get some custom speedo setup because apparantly the RX8 trans doesn't have a gear for the speedo cable.

I myself was wondering about this idea. I'm interested in doing the 6-speed swap....

Did you put a t2 drive shaft in it yet to test the tail section to make sure the splines fit?

the rx8 has known problems of tranny breaking at high horsepower. I've even heard stories of breaking just by running at the track with slicks. I don't think it'd be a very wise choice. Keep looking around.

Hmm im just waiting for reted or Nz to start posting, and literally shatter all of our hopes ;)

Well my friend said the TII and even the FD driveline fit. He was going to put it into his vert but lost interest. I asked him about how strong they are and he said the way it was built it looks just as strong as a TII or FD trans. HE said regardless of the trans if you have a dipshit driver downshifting from 10k rpm from like 2nd to 5th then that shits going to happen. However I've only got a mildly modded S5 N/A engine so power handling isn't an issue. And besides. Name one FC or any 7 with a RX8 trans. I'm going to make the measurements myself with it side by side with a TII trans.

Guys, I really wouldn't do this if you're going to be putting much power through your car, like turbo guys for example.

The RX-8 transmission is NOT strong at all! It is built to handle stock and a little past stock but can die soon after. There are RX-8 owners that have broken their trannies at 250rwhp. That is a rare occasion as most that break them have 270+ rwhp, but there have been cases of them dying at as low as 250.

Also, I'm not sure how well it would fit. From what I understand, or have heard, with RX-8 owners that have too much power for the stock tranny they are switching to FD transmissions, but don't quote me on this because this is just what I recall reading. I think what I read is that the FD tranny is a pretty good match and fit, but if that's the case I'm not sure how well it'd fit in the FC without modification as I didn't think the FD tranny was a drop in for the FC. Once again I can't remember exactly but this is just what I'm recalling.

There are other factors that make the RX-8 a totally different drive than just the ratios of the gears in the tranny. I don't really think this is a good idea, especially someone with a turbo for example. I'd just stick with a TII drivetrain and be happy with that.


Oh I just recalled a situation of the stock RX-8 tranny breaking. JudgeITO had a completely stock RX-8 except for a "special" streetport done to his engine. There was absolutely no change besides the streetport, and he broke his transmission. I think Mazda addresses this with the late 04's and 05's, though, because it seemed all the people destroying their trannies were 03 and early 04. Plus, since then JudgeITO has done tuning and added a bunch of nitrous, so I'm guessing the later model ones have it worked out, because he had his replaced (obviously).

Horsepower does not break gearboxes, torque does. Compare the RX-8's 164ft-lb to the S4 TII's 183ft-lb and the S5 TII's 196ft-lb. Suddenly an RX-8 gearbox behind a modified 13BT doesn't seem so smart...

Are you sure about that?

Sorry about that... ;)

I know I'm not ;)

You guys should really do research about this on rx8club.com, not rx7club for how much they can handle :rolleyes:

Did I mention that this won't be bolted to a turbo motor? The decision has been made as far as that goes. If I'm going turbo then I'm going FD. However a lightly modded N/A with close gears and a 4.30 rear end will surprise a few people and be my daily driver. I'm just looking at the cost and hassle (guessing it will be the same as doing an auto>5speed swap) to see if its worth it. I'm not worried about the 160 hp this motor puts down breaking anything.

the renesis rotary is claimed 240 hp stock. A s4 t2 is 180..... an s5 is 200 i belive.... Shouldnt be a problem, should it?

.

You know, I did alot of searching last week on NA trannys. There were a few people here that said the NA was used up to 500hp, even on non rx7 cars.

They all agreed on one thing, dropping the clutch will kill the tranny.
If you can do a launch without hammering the shit out of the tranny, apparently it can take it. Its been discussed before, you just have to be carefull and smart, as in, not do a burnout all the freakin time ;)

Im not making that shit up, I searched it and found those comments.

lots of good info....

I know Kevin Landers had an N/A tranny on his turbo vert when he had it and the gears got eaten to shit. He had a thread to show the tear down of it and basically all the gears except 5th/revers got ground to nothing over time. And he didn't have 500hp that's for sure.

Basically, NZ's still right. By dumping the clutch you're applying a shitload of torque instantly (which will slaughter it) By being gentle and just accelerating, you're not applying torque so violently and you're applying less of it, this will of course be a lot easier to deal with, but eventually the parts are going to wear and/or break depending upon just how much torque you feed it.

Based on what I have been told, that's the bottom line. As I understand it, the RX-8 gearbox is the same as the Miata 6-speed. For the Miata or the stock, low-torque Renesis engine, it's just fine.

Some people who are upgrading their RX-8s are going to relatively low-priced T-II gearbox's to handle the higher power.

I was considering going to a 6-speed for my stock convertible and adding a 4.3 rear end. This notion was based on the mistaken belief that the Mazda 6-speed, like the Chevy (Camaro) 6-speed had 4th as it's 1:1 ratio and two overdrive ratios above that. However, the Mazda gearbox has 5th as its 1:1 and a numerically higher 6th gear than the T-II gearbox, so I couldn't see any advantage.