This is my first post on a forum so I hope I did not mess something up.
I am currently planning to fit a 5-Speed transmission from an RX-8 with the 192hp into my FD because it is a lot cheaper to get here in Austria than a good used RX-7 transmission.
The facts that I have already found is that you can use the bell housing and the tail shaft housing of the FD transmission and bolt it right onto the RX-8 transmission.
This way, you maintain the pull type clutch and the original shifter location of the FD. Also the gearing is very similar to the original FD transmission.

Now to my question: Before I buy the used RX-8 Transmission I want to make sure that the output shaft of the transmission fits onto the FDs Driveshaft.
I found this picture of the RX-8 driveshaft where I can count 25 valleys and 23 splines. But i did not find the outer diameter or other dimensions of the yoke.


RX-8 Driveshaft Splines

If anyone that has a RX-8 and a RX-7 FD driveshaft/propellorshaft lying around and could measure me the outer diameter and confirm the number of splines I would be very thankful.
Thanks to everyone!

 

Only 6 speed rx8s were sold here. Measured the OD and spline count on both for someone on here in the last year or two and they were identical.

Import rx8 5 speeds have been sold here for a few years as FD boxes once the extension housing and bellhousing were swapped....so I think you're safe. If really paranoid, I'd just get the part number for the 5 and 6 speed tailshaft and see if there's any difference?

 

Thanks a lot billyboy that was exactly the confirmation that I wanted to hear.
Have a good one!

 

^Yep, I personally know 2 people who have done the swap with a JDM 5-speed and it was just change the bell housing and tail housing and bolt up from what I understand.

Dale

 

Yup also common for rx8 REW swap builders to buy an rx7 trans and swap the tail end and bell housing for it to work.

 

Awesome, thank you guys for all your info!

 

I actually thought you were asking about the driveshaft itself. I don’t think the carbon shaft of the 8 can be bolted into place of an FD’s??

 

it’d be surprising to me if they match up in exact length, but if somebody wants to post up a diagram indicating the measurement points and length between them I can compare it to the same on an RX8 CF driveshaft and report it back here.
.

 

Sorry if it was not clear. The driveshafts of the FD and the Rx-8 are not interchangable because of the difference in length. But I needed to know if they have the same number of splines and the same flange bolt pattern for the diff.

And because that is the case, I can use the RX-8 5 Speed Manual Transmission in an FD with the bellhousing and tail of the original FD Transmission.

 

the only thing to be aware of is that while the RX8 5-spd has additional cone synchros it’s been reported that they made the gears narrower width to accommodate them.

in theory those gears might be weaker, the particular Rx8 Renesis engine used with it was only rated 192 bhp.
.

 

I think for any car seeing less than 400hp the RX-8 5-speed will be fine. The FD gearbox holds a LOT of power, I've seen 500+ on it. The fact the RX-8 gearbox is newer and most likely built with better materials than the original gearbox from the earlier 90's probably helps too.

Dale

 

This poses an interesting thought. While the RX-8's gears are ridiculously short in the six speed box, would one theoretically say that you could take the six speed box, swap the bell housing and tail shaft with FD five speed components, and have a bolt up option that retains the speedometer *and* stock shifter location? I know the RX-8 gearboxes don't have a provision for the speedometer sensor, as it uses the wheel sensors, so this was a question I had myself.