an Rx-8 R&P set mount in an FD diff housing and vise versa

 

For the more simple minded of us,<-- could someone give a brief summary of what kind of differences having a higher or lower gear would mean for the good ole' 7?

 

In short...
Higher ratio = shorter gears = faster acceleration, lower top speed
Lower ratio = longer gears = slower acceleration, higher top speed

 

Ok, but then you have to use RX-8 torsen instead of FD stock torsen?

 

If the ring and pinion are interchangeable, then you would only have to swap out the ring and pinion...

unbolt old r&p, bolt on new r&p, set backlash. done.

 

NO, bolt the ring gear to which ever Differential was from your car or aftermarket, Kaaz, OS Giken, Gleason-Torsen, Quaife that fits your car.

The R & P are interchangable between the FD RX-7 and FE RX-8.

 

Ok, then RX-8 is 8" and other articles mentioning it like 7" is wrong, correct?

 

I never mesured either one. But Mazda says they are interchangable with the same bolt holes and my 4.3 in an FD has an RX-8 part number

 

I realize this thread refers to the R&P/final drive.

The actual diff itself is interchangeable, correct? I've been told it is, but am looking for those who have actually done it. thanks.

 

That would be interesting.

I bought a 4.44 RX-8 diff with 5k miles on it to swap the R&P into my FD Diff.

But if the diff bolted up to the FD...

Anyone know any more about this?

 

Interesting. I've wondered about putting a 4.3 in myself, and the 4.44 might be an interesting swap as well. I think the 4.77 gears would be way too short. Though at 500+ HP the stock 4.1 might be just as well. So many choices. If the rx8 guys want our 4.1 for gas mileage then might be able to find some direct trades. could be a cost effective way to get new gearing.

 

Yeah if you go on the 8 forum and post for trade you'll get some interest. When I was looking into doing this I was contacted by a couple people. Then i decided to stick w/ my 4.1 since its a DD.

 

Folks reading this thread may find this of interest.

Several model years of the Kia Sportage have Mazda 4.77 gears in the front diff.
Kia Sportage Gears Page 1

Kia Sportage Gears Page 2

Of note to folks that want > 4.77:

Aftermarket Sportage gears are available in 4.875, 5.25 and 5.38

 

I was thinking about doing it till this reminded me. Haha.

 

Sadly, I have learned this will not work for the FD.

These are 7" ring gears and the FD uses an 8" ring gear.

It seems reasonable though that there are other cars using R&P in the correct size for an FD, and possibly desirable gear ratios.

 

sorry for the BUMP ...

i have an FC t2 and i would like to put a 4.44 gear set (r&p) from the RX8 ...

are the gears interchangeable and will it fit on my diff ???



thanks guys

 

Sorry, will not work for your FC

pinnion gear shaft, is to short for a FC diff housing

 

I thought I might add.

I was just pricing the 4.3 ring and pinion for the FD from Mazdaspeed, and the website substitutes it for the Rx8 version when I check availability.

 

that's because they are literally the same thing

 

So I bought a complete rear end from a automatic 2004 RX8 to use the gears and bearings, I wanted to try the 4.30 gears that someone said in this thread came in the automatic rx8s. So I just took it apart and counted the teeth and its a 4.44, and I just called and verified it was a automatic, so this sucks I wanted the 4.30 gears and dont think I want the 4.44 gears for drag racing. I also bought it cause I am pretty sure my pinion bearings are bad cause it makes a loud noise so I was gonna use the bearings from it too.

 

Sucks that the Rx8 version is about $100 more

 

So... I'm not disputing whether the Rx8 and FD r&p's are interchangable. Several people stating they are.

So... my question is: Is the FD 7" or 8"? Because both the FD and Rx8 MUST be the same size for this to work, hence they are both either 7, or both 8. I suppose it doesnt really matter... I'm just curious.

Anyone got one sitting outside of the case and care to measure? Measuring either one should be sufficient for both since they are interchangable.

 

Pretty sure they are both 8".

I have an RX8 diff assembly in a box in the garage, I will measure it when I can get back out there. ( have work to do here first)

The RX7 diff case will get cracked open real soon now, it's sitting on a tranny jack.

The RX8 diff with 4.44 gears will be for sale BTW.

Bought 4.77 gears and Carbonetics diff instead.

 

It was already said in this thread that it is 8", and just to double check (since there is other incorrect information in this thread that said I would be getting a 4.30 gear set from a 2004 automatic rx8), I measured it and it is 8".

 

I am also going to sell my 4.44 gears, and the RX8 differential and housing if anyone is interested.