Originally Posted by WIDEBODY7

They should bolt right on.

Originally Posted by jimlab

Well, that and you'd have to figure out how to keep the powerplant frame and transmission from dragging on the ground, since the FD PPF bolts to the rear of the stock 5-speed and supports the transmission and differential.

Also, the gear ratios are less than ideal for the FD.
1st 3.76:1, 2nd 2.27:1, 3rd 1.65:1, 4th 1.19:1, 5th 1.00:1, 6th 0.84:1.

The 0.84:1 6th gear would put the engine at about 3,250 rpm @ 70 mph, which would burn up your tank pretty quickly compared to the stock 0.72:1 5th gear @ 2,700 rpm. In fact, you'd be at higher rpm in every gear except 5th (same as the 5-speed's 1.00:1 4th gear) at any given speed, and you'd be shifting more often.

It would also cut top speed to ~172 mph with the stock 4.10 differential gears in the manual, ~181 mph with the 3.90s from an automatic. To be able to even break 200 mph with the RX-8 6-speed, you'd need a set of 3.42:1 gears... which don't exist for the stock FD differential. To get to 220, you'd need a set of 3.07:1 gears, which don't exist either.

As far as the length of the RX-8 6-speed, you'd probably end up having to have the driveshaft modified, and the shifter may not match up to the stock opening. I don't think that anyone's confirmed that the bellhousing bolt pattern is identical to the stock 5-speed either. How about adapting the FD's slave cylinder to actuate the RX-8 clutch? Would you like me to keep listing more potential problems with this swap?

Originally Posted by Mousetrashdiver

Did they make a 6 speed tranny for our cars?