So a friend of mine has a rx8 six speed sitting at his house, and he was wondering if I could use it.

My 1st and 3rd gear synchros are going out on my 82, so I was going to pull it to rebuild. I was going to be lazy and put a S5 transmission (I have one laying around), but I remembered that's too long. So when my buddy brought up that he had a six speed my mind started turning...

The six speed should be 3.5 or 4in shorter then a Fc trans, and the Fc trans was about 2in longer then the Fb? Correct me if I am wrong! Its been sometime sense I have seen them next to each other.

So the Rx8 trans should be 2in (or around there) shorter then the Fb trans. Now that means I get to move the motor back a little bit to keep the stock shiftier placement. And moving the engine back with help with handling, so that's kind of a bonus too.

I know final gear ratio from the 5 speed to 6 speed is not that much differences. But putting a gear between 3rd and 4th... well I have felt the need for it on the back roads lol.

04-08 Rx8 3.760 2.269 1.645 1.187 1.000 0.843 Axle 4.440
79-83 Rx7 3.674 2.218 1.433 1.000 0.825 Axle 3.909

I also have a GSL-SE rear end I am going to toss on with 4.444's... FUN!

So all I should need is a starter, driveshaft, clutch, flywheel, slave cylinder... Anyone see a problem or a hole with this plan?

 

not sure about fitment ect, but your speedometer will not work with the rx8 tranny as the rx8's is ran off the wheel speed sensors, so theres no where to plug in a older cable driven speedometer.

 

My question is WHY? The FB transmission can take much more of a beating than the rx-8 transmission. The rx8 transmission is made of glass.

I did well over 100 drag launches in my FB, but ive done like 2 in the 8. I know its going to grenade. If I ever go FI, I'm going to really consider a trans swap.

Also the speedo cable issue as Ryan mentioned.

 

The speedometers plan was taking out the stock gauge cluster, and replacing them in the same place to keep that stock feel with aftermarket ones.

Why? Well not? I like sixspeeds for one, and I think they are more fun to drive. I don't do drag's, track days, or any real beating. Plus I don't think a street ported 12a will be as bad as a Renesis. A few less Rpm's, and not as much power... its it really that bad of a transmission?

 

u mentioned flywheel, keep in mind you cannot use the stock rx8 flyhweel, you would need to use a 12a automatic counterweight ( i think they vary by year slightly in rotor weights) then an aftermarket rx8 flywheel. as the rx8 oem unit wont balance right iwth the 12a

 

The point is, you need something to drive the speedo signal. If you use the RX-8 trans, you dont have any way to hook up the speedo cable. You dont have wheel speed sensors to drive any other type of gauges on a FB. Not to mention having to buy a new flywheel and clutch setup like ryan was mentioning. Plus a starter too!

The point I am getting at here, is you would be doing a lot of work for basically no gain at all. There's nothing wrong with the 12a transmission if you aren't boosted.

Coming from someone who has owned both the rx8 and multiple FB's, I wouldn't do what you are attempting.

 

For now I might take your warning, and do the project when there is more to work with.

Random question, are the syncros the same from year to year? Have a S5 trans with a broken bell housing (droped off a tall shelf) but the syncros are still good. So I was going to gut it, and put them in the FB trans.

 

Not sure on the syncros. If its a tII transmission definitely not. The n/a transmissions are somewhat related. Ive never gutted both of those transmissions to compare. I believe you can swap the entire gear set, but not sure about just the syncros.

 

Throw the rx8 6speed in, buy a GPS speedo, (Speedometers Gauge, Speedhut Gauge Series by SpeedHut) be done, assuming the trans is free/cheap. With the average FBs power/weight, I'm sure that trans will live a while. I would imagine it would live the same life as in a NB miata.

 

Main thing here on reliability is that an FB weighs a lot less than an Rx-8 and has a lot less power. It will work perfect. I am sure that ACT makes a clutch that will fit the 12A with the center section splined for the TII or Rx-8 trans. That way there is no need to redo the flywheel.

I had never heard of there being a length difference between the smooth case transmissions. I know on my old 1st gen I went through about 7 transmissions of all years on the same drive shaft.