FD and RX-8 Diffs interchangeable?

jkstill · 06-16-2009, 12:22 AM

There's a thread at the other forum discussing interchangeability of RX-8 and FD differential parts.

http://www.rx7club.com/showthread.php?t=797818

It is known that the 4.44 ring and pinion gears from an RX-8 manual diff will bolt up into a FD diff.

That seems a nice compromise compared to the 4.77 gears that many autoxers use. While I autox my car, I also do track days, so the 4.44 would get me out of the corners faster in 2nd gear at autox speeds, but still be tall enough for track use.

So, I bought a low mileage 2005 RX-8 Manual diff with the 4.44 gear set.

The question that remains unanswered is this: Does an RX-8 diff bolt right up to an FD? There are indications in the other thread that this might be true, but no solid answers yet.

If so, that would sure simplify getting the 4.44 gears in my FD.

Anyone here know?

I was going to look on the rx8club.com forum as well, but it is currently down.

afgmoto1978 · 07-15-2009, 05:47 PM

I too would like to know this.

prrex4ever · 07-15-2009, 06:26 PM

Quote:

Originally Posted by afgmoto1978

I too would like to know this.

I also wonder if they are any stronger.

jkstill · 07-16-2009, 01:34 PM

This thread indicates that 4.77 gears from a Kia Sportage can be put in an FD diff - for < $300.

http://www.hacstl.com/forums/showpos...81&postcount=9

Apparently this is fairly well known in the S2000 Community.

afgmoto1978 · 07-16-2009, 02:47 PM

I forsee having two diffs, one with a 4.44 and another with a 4.77 depending on the track and event. Hmm...

Monkman33 · 07-16-2009, 04:11 PM

I am definitely going to get a 4.44.... but that 4.77 is very tempting for autocross...

Does anyone make a taller 5th gear? Then I could run the 4.77's and still be able to hit the freeway every now and then.

afgmoto1978 · 07-17-2009, 02:34 PM

Well had an close look at the RX-8 Diff and it won't work with FD powerplant frame or diff mount. Bummer.

Rotary Inspired · 07-17-2009, 04:41 PM

I have read you have to remove the gears and put them in the FD Diff. Hope this helps.

sk8world · 07-18-2009, 09:20 AM

better be just the gears. I just bought a 4.44 ring and pinion to go in for drag racing.

jkstill · 07-18-2009, 11:12 AM

Quote:

Originally Posted by afgmoto1978

Well had an close look at the RX-8 Diff and it won't work with FD powerplant frame or diff mount. Bummer.

From what I have read I think the internals may be interchangeable.

I had the entire RX-8 Diff - it was pretty obvious that the complete thing would not be a bolt in. That would have been sweet.

Whenever I get around to the swap, I will find out if the diff assembly is interchangeable.

SPICcnmFD · 07-20-2009, 08:18 AM

That would be really nice if they are. I've been wanting a diff. set but IMO 4.3 isn't worth the money and 4.77 is just to much. I've always wanted something close to 4.5.

Monkman33 · 07-31-2009, 01:39 PM

Quote:

Originally Posted by SPICcnmFD

That would be really nice if they are. I've been wanting a diff. set but IMO 4.3 isn't worth the money and 4.77 is just to much. I've always wanted something close to 4.5.

So the 4.44:1 isn't close enough to 4.5:1 for you?

SPICcnmFD · 07-31-2009, 07:03 PM

Quote:

Originally Posted by Monkman33

So the 4.44:1 isn't close enough to 4.5:1 for you?

Yes it is that's why it would be nice if it's interchangable.

Chadwick · 08-04-2009, 11:22 PM

Only the RX8 ring and pinion can be used as a replacement in an RX7 diff, you can not use the RX8 differential case or differential.

Hope this helps,
Dan

06-16-2009, 12:22 AM	#1
jkstill Rotary Fan in Training Join Date: Mar 2008 Posts: 93 Rep Power: 18	FD and RX-8 Diffs interchangeable? There's a thread at the other forum discussing interchangeability of RX-8 and FD differential parts. http://www.rx7club.com/showthread.php?t=797818 It is known that the 4.44 ring and pinion gears from an RX-8 manual diff will bolt up into a FD diff. That seems a nice compromise compared to the 4.77 gears that many autoxers use. While I autox my car, I also do track days, so the 4.44 would get me out of the corners faster in 2nd gear at autox speeds, but still be tall enough for track use. So, I bought a low mileage 2005 RX-8 Manual diff with the 4.44 gear set. The question that remains unanswered is this: Does an RX-8 diff bolt right up to an FD? There are indications in the other thread that this might be true, but no solid answers yet. If so, that would sure simplify getting the 4.44 gears in my FD. Anyone here know? I was going to look on the rx8club.com forum as well, but it is currently down.

07-17-2009, 04:41 PM	#8
Rotary Inspired Rotary Fan in Training Join Date: Feb 2008 Location: SW OKC Posts: 75 Rep Power: 18	I have read you have to remove the gears and put them in the FD Diff. Hope this helps. __________________ If you wanna become ASE certified buy the RX7.

07-18-2009, 09:20 AM	#9
sk8world 600rwhp club member. Join Date: Mar 2008 Posts: 551 Rep Power: 18	better be just the gears. I just bought a 4.44 ring and pinion to go in for drag racing. __________________ 6.? @ 11? drag pass http://www.youtube.com/watch?v=9wfxT2RMr7c

07-20-2009, 08:18 AM	#11
SPICcnmFD Rotary Fanatic Join Date: Feb 2008 Location: B'ham, AL Posts: 329 Rep Power: 18	That would be really nice if they are. I've been wanting a diff. set but IMO 4.3 isn't worth the money and 4.77 is just to much. I've always wanted something close to 4.5. __________________ 1993 Rx-7 SM2 #11 At the local AutoX: http://www.youtube.com/watch?v=9VOSQkkSLQs Speed for Sale shootout 2007: http://www.youtube.com/watch?v=JiqlyAkGmpg A few laps at Barbers: http://www.youtube.com/watch?v=6_h5q...x=0&playnext=1

08-04-2009, 11:22 PM	#14
Chadwick Rotary Fanatic Join Date: Feb 2008 Location: Smyrna, TN, USA Posts: 239 Rep Power: 18	Only the RX8 ring and pinion can be used as a replacement in an RX7 diff, you can not use the RX8 differential case or differential. Hope this helps, Dan __________________ 93 RX7 BB (Race Car) 93 RX7 SSM (Soon to be IBM and a daily driver) 05 Silverado Z71 08 Mini Cooper 80 LS RX7 (for sale)

07-15-2009, 05:47 PM	#2
afgmoto1978 Rotary Fanatic Join Date: Mar 2008 Location: Portland, Oregon Posts: 381 Rep Power: 18	I too would like to know this.

07-16-2009, 01:34 PM	#4
jkstill Rotary Fan in Training Join Date: Mar 2008 Posts: 93 Rep Power: 18	This thread indicates that 4.77 gears from a Kia Sportage can be put in an FD diff - for < $300. http://www.hacstl.com/forums/showpos...81&postcount=9 Apparently this is fairly well known in the S2000 Community.

07-16-2009, 02:47 PM	#5
afgmoto1978 Rotary Fanatic Join Date: Mar 2008 Location: Portland, Oregon Posts: 381 Rep Power: 18	I forsee having two diffs, one with a 4.44 and another with a 4.77 depending on the track and event. Hmm...

07-16-2009, 04:11 PM	#6
Monkman33 Still Building my FD Join Date: Jun 2009 Location: Pasco, WA Posts: 255 Rep Power: 16	I am definitely going to get a 4.44.... but that 4.77 is very tempting for autocross... Does anyone make a taller 5th gear? Then I could run the 4.77's and still be able to hit the freeway every now and then.

07-17-2009, 02:34 PM	#7
afgmoto1978 Rotary Fanatic Join Date: Mar 2008 Location: Portland, Oregon Posts: 381 Rep Power: 18	Well had an close look at the RX-8 Diff and it won't work with FD powerplant frame or diff mount. Bummer.