Hey guys i have a 07 6spd auto rx8 im wanting to put a carbonn fiber driveshaft from a 6spd manual car. Will it fit properly & is there a difference between the mt c/f & the at steel driveshaft. Thanks for any advice.

 

THats a good question, wasnt 100% sure but i dont think u could. Mazda use fiber on mt because of the rpm. Something at doesnt have

 

I believe they are different lengths......

 

I was hopeing i could save weight with the cf drive shaft. If anyone can post dementions of the steel vs carbon fiber driveshaft plus u-joint differences. I would greatly appreciate any more info. Sadly theres no rx8 guru around me that i could ask. i hope this thread will be able to help future rx8 owners/modifyers who would want to perform this swap

 

i thought the drive shaft in the a/t was aluminum not steel but i may be wrong

 

same length, but i wouldnt recommend it.. mazda used the steel ones for a reason. it could be that during their testing the AT starting to damage the carbon ones for whatever reason over time. who knows, but better safe than sorry. you dont wanna get stuck somewhere because of a drive shaft. theres nothing wrong with the AT shaft, and i plan to use it when i AT to MT swap since it will be more durable. but hey thats just me, to each their own. good luck whatever you decide

 

Nope OEM auto was steel, and you can actually get an aluminum which is lighter than the CF and about 7lbs lighter than the OEM steel, and 700 bucks cheaper FYI

RX8 transmission

As far as direct swap I have no idea, but I doubt it I'd contact this vendor and ask.

 

thanks for clearing up my mistake. i dont have much experience with autotragics

 

it's not about weight.

 

Explain why CF would be better than aluminum, scratch that quick link for OP

http://theattack.rallysportdirect.co...shaft-overview

Personally for an A/T doesn't seem worth it I'd still go with aluminum

M/T is a different story though.

 

I can't speak for the 6A/T but the 4A/T steel shaft fits fine on the back of the 5M/T and 6 M/T, so it would stand to reason they wouldn't make a separate propshaft just for the 6A/T.

Someone above mentioned the CF propshaft was put on for RPM. Is this because the rear end in the M/T has a different ratio than the A/T that would cause the M/T propshaft to spin at a higher rate of speed than the A/T one at similar speeds? Because it sure as hell doesn't have anything to do with engine RPM.

 

I tried to search on something and this thread came on my result. so I figure maybe I should answer this

Carbon was used because of stability, it's easier to balance.

most important is, at 9000 rpm Aluminum/Steel will not hold for an extended period of time, it's pretty much the same thing why Mazda don't want you to rev over 10,500 rpm on stock steel flywheel, it's gonna disintegrate and cut ur leg off.

and Mazda was desperate to try to reduce weight on the car, that a pound or 2 might not seem much, but it adds up.

 

I always wondered what drove the rpm cap

 

Maybe for the flywheel but I say again, the rpm of the propshaft has nothing to do with engine speed and everything to do with vehicle speed / rear wheel speed.

The prop shaft doesn't care about engine rpm, it just sees output from the gearbox and transmits it to the rear end... The faster the vehicle speed the faster the prop shaft speed

 

this

 

I was refering to the flywheel

 

Brother, you're a really smart dude and I respect your experience and contributions on this forum but I have to say again that I disagree.

The RPM of the flywheel has nothing to do with the RPM of the propshaft and everything to do with the gearbox's output / rear end ratio of the car.

Go ahead, put that bad boy in 1st gear and wind it right out to 9k. You'll be going what, 30mph? 40mph? The propshaft will be rotating at however many RPM it needs to at 30mph. Say for the sake of argument its X rpm.

Put the car in 5th at 30mph, the engine is rotating at 1200 rpm or something absurd, guess what? The propshaft is still rotating at X RPM, as it was when you were bouncing off of the rev limiter in 1st at 30mph.

 

The CF driveshaft was used as part of the Sports Suspension package to improve engine response only. It has nothing to do with RPM, and the steel driveshaft used in the base A/T has everything to do with cost savings and nothing to do with strength. There is no logical reason why the steel shaft would be superior for the Base A/T, and Mazda "downgraded" to the carbon fiber for the Sport, Touring, or Grand Touring A/T.

CF would be superior to aluminum due to strength, namely a rotational shock of a torque hit from a clutch drop or something. Aluminum would be superior to CF for shock received from any other angle, but that isn't a concern unless the driveshaft is out of the car or the car is in subjected to a severe accident.

The driveshaft runs at a fixed speed based on the speed of the rear wheels, and the relationship of those two speeds is entirely calculated by the overall gear ratio of the rear gear + the "ratio" of the rotational diameter of the tire. RPM has nothing to do with it as plenty of people are pointing out. This is true of both the A/T and the M/T.

 

Sounds like some confusing between drive shaft and torque converter properties.

 

you have a point, I got it confused myself. like RIWWP said, it has to do with higher strength.

 

i wouldn't bother, the auto is a power hog and the differences won't be worth the cost. there is going to be a difference in length and most likely the output shaft spline count on the auto versus manual anyways, a modified version would have to be made.

if you want better response get a manual 6 speed.

as i say to anyone with an auto RX8 who wants more performance, you bought the wrong car.

 

RR did the swap before and he said the length is the same between cF and steel shaft.

 

the yokes match up?

if it's a direct swap then it could be considered. if the yokes need to be swapped then i wouldn't bother. a good used CF driveshaft can be found for about $100.

 

For possibly the thousandth time on this forum: stock 6 SPD CF prop shaft will work on the 4at and 5mt cars. I know because I have done it.

I put a 4at steel shaft behind a 5mt and then swapped in a 6 SPD CF shaft and both fit perfectly. Splines, length, interface with the rear diff... It is literally a direct swap. Its not a discussion, it is fact. The end.

 

that's nice, as if people really spend much time searching for this particular discussion.

but i think what people MIGHT be interested in instead of the search **** proposal would be what your impression of the change was.