Please only post here is you have done it or know from 1st hand experience

I already know the actual diff unit is interchageable

Why do I want to know?

I have an RX8 Diff with about 1400 miles on it from a 2004 HI-output RX8, R&P ratio is 4.30:1 . I also have a OS Giken locking Diff unit with less than 500 miles of use. I want to take the R&P out off the RX8 diff housing, bolt up the OS Diff, and put all 3 parts inside an FD3S Diff housing and then put the diff in my FD..

Maybe some one has already done this?

 

I'm pretty sure the RX8 diff is significantly weaker than the already weak 3rd gen torsen. Someone correct me if I'm wrong, but I thought the RX-8 drivetrain was the same as used in the 6 speed miata.

 

Maybe I was unclear..

I am only interested in finding out if the RX8 and FD3S R&P gears are interchangeable.. Thats all...

I want to use the RX8 4.30:1 R&P Gear inside the housing of an FD3S Diff..


And yes the FD3S housing is weak until you use a properly built brace..

 

K I misread your post. I'll see what I can find out.

 

I remember searching a few months ago on both RX-7 and RX-8 forums and apparently the RX-8 guys used our R/P for better gas mileage.

If you search for the user "Mazmart" they were selling diff swaps with 3.90 and 4.10 R/P's. Perhaps the R/P's were from the 3rd gen?

Nothing definitive but it may give you some leads.

 

yes.

some drag guys do it. speed_nyc did

 

BTW, I think the new RX-8's have like a 4.7 stock or something.

Party on, Wayne.

Dale

 

Ok, sounds like it will work.. I will get going on it.. maybe do a small right up with pics here later in the month...

 

Heres something i was wondering since i just read the OP.

Do certain, most, or all Japan FD's have a shorter Final drive ratio of 4:30?


My reasoning behind this is if for some reason the OP cannot make the RX-8 R&P swap work theres always the JDM FD R&P to look at which is just a simple swap

 

Yes, there are models of the FD in Japan that came factory 4.30:1 R&P. The Jspec RZ and R models came with 430's.. I have had them in the past but they are hard to come by in Japan..

 

Um... I was actually on the RX-8 forums trying to find an R&P for my FD, and their stock ones have a 4.40:1 ratio

 

Think it's a myth thats been propagated on here unfortunately.

If the car came standard with 17" wheels (and as Japan2LA pointed out), that means RS/RZ/Spirit R, you'll have a 4.3. Bizarrely and probably more so now with the exchange rate they are cheaper new in the US than Japan, last I checked.

 

Earlier RX8s had 4.3 or 4.1. Later they changed that to 4.4. I forget the year it happened.

 

correct info from mazda rx-8 brochures:

Manual trans
4.444:1 2004-2008
4.777:1 2009

Auto trans
4.30:1 all years

 

the rx8 4.30 is the same part number as the rx7 4.30 gear set

 

So to sum this all up.......RX8 R&P's will swap into a FD Diff?

 

Does anyone know anything about the rx8 trans.? I would assume it would not hold up in an FD with any kind of mods.

 

The Rx8 gearbox is an Aisin unit that would not hold up to high horsepower numbers. Rx8 gearboxes have been fitted on FDs before also.

They would hold up perfectly fine on a stock turbo power or N/A Rotary.

The gearbox is also the same as the S15 Silvia Spec R, which is known to be weak also. They get swapped out for 5 speed S14 boxes, Nismo 6 speed trannies, or dogboxes.

 

to me, the 4.44's would be great for a street car/autocrosser...

 

Just changed out my backup diff to an RX-8 4.44 R&P with no problems. Can't wait for Autox to start.

 

Yes, I pulled the 4.30:1 R&P out of the RX8 Diff I had and they are the same as FD3S.. I have not swapped them over to the other FD3S housing yet..

Anyone want the RX8 Diff housing? I have ZERO need for it..

 

I'll take the diff housing off your hands. Have any complete s5 engine trans packages as well ? A couple of friends are looking for a set here in Idaho. PM me if you dont mind.

 

Hey Mike

Is RX-8 7" or 8" diff....

FC NA is 7"
FC Turbo and FD is 8" (and internals are swapable, we are running FD torsens in our FC diffs)


As it was mentione before, RX-8 came with 4.44 gears, now in 2009 model with 4.77 gears.

Quoted from turbo magazine :

It seems Mazda has been sourcing out its gears to Honda S2Ks and '94-'02 Kia Sportages 4x4. The front axle of the Sportage has a Mazda 4.778 ring and pinion (part number MM05727110)

http://www.turbomagazine.com/tech/08...ech/index.html

S2k is 7" (yes or not?)
Kia Sportage is 7" (yes or not?)
Mazda RX-8 is 7" (yes or not?)

FD3S (8") gears cant be then interchangeable with RX-8 (yes or not)

 

Don't start this again.

FD Rx-7 and FE RX-8 R&P's are interchangable.

 

I understand that whole differentinal assembly could be interchangeable (same mounting points into chassis/subframe, same pattern for driveshaft and halfshafts would fit)

But, if internals are 7" on RX-8 and 8" on FD then these cant interchange (RX-8 gears into FD diff housing assembly and vice versa)

If they do interchange, then they are 8" and Kia/S2000 does not fit, or they are too 8"

Anyone has a pics of internals of FD / RX-8 diff side by side?