Hey guys -

I'm out here pioneerin' mods again for you good folks .

First part of the credit has to go to my buddy Jimmy, he did the initial legwork on this.

The RX-8 manual transmission uses a 4.44 ratio ring and pinion. The FD stock ratio is 4.10, FD auto is 3.90. A higher ratio gives better acceleration due to mechanical advantage, but at the cost of top speed and extra RPM's when cruising on the interstate.

Going to a 4.30 final gear has been a popular upgrade for a while, but unfortunately this is QUITE pricey. The good news is there's a ton of RX-8's out there that are gettin' wrecked up good, ready to donate a nice diff to ya.

So, what are we talking? I found a whole RX-8 diff, low miles, on Ebay for $180 SHIPPED. Yep, that's pretty cheap.

Got it, broke the diff down and removed the ring and pinion. Removed my diff, took it to a shop with the RX-8 ring and pinion, $100 later they were swapped in and professionally set up. Popped back in the car, good to go.

If you are going to do this, you'll need a few parts too. Here's the list -

- Pinion nut
- Pinion seal
- Driveshaft seals (2)
- Front crush tube

Those are the MANDATORY parts, you can also get new bearings or races if you like. Mine were in great shape so I let it ride. Cost of parts wasn't bad, I'll have to look up part numbers/pricing later.

Next thing I found was the aluminum rear cover on the RX-8 diff I got was different. It has a small kick-out on the driver's side and more cooling fins. The part number on it is RA12-27-320E, Ray Crowe quoted me $120 for it, which is VERY reasonable. Best part is it bolts right on, fits perfectly, no modding or anything.

Attached are pics of the new cover off the car compared to my dirty FD cover, and the diff in the car. Will it make a difference? Hard to say, probably a good idea if tracking the car, but it's just damn cool and it came fo free with my RX-8 diff.

There are different gear ratios for the RX-8 and I need to do some more digging on that. The newest RX-8's have like a 4.7 or something stock, which is REAL aggressive on a street car.

BTW, you don't have to hit Ebay up for these, your local junkyard is a great source too. RX-8's are new and plentiful enough that a good junkyard should be able to source one quickly and for a good price.

Dale

 

Very cool, good job!

 

Dale - thanks for figuring this out for us. why did you pop in an RX8 cover? was it because the internal ring gear was too big such that the FD cover didn't fit?

Also, what type of shop did the differential assembly?

Thanks in advance.

 

that cover is a good deal!

we know the gearsets swap over, the auto Rx8 gearset is the same part number as the FD, and all the bearings and such are shared too.

i haven't looked at the 09's though...

 

Nice, I like that cover!

 

Very cool, thanks for sharing Dale!

 

The used diff I bought came with the cover, I saw it looked way better than the FD cover, so I put it on . The gearset is exactly the same size, you can run it with the stock FD rear cover no problem.

The shop that did the work here in Pensacola specializes in old car restorations and stuff. I went there because Jimmy used that same shop to do his swap. Last time I did a gearset swap (on an old project car) I found a guy that does diffs for 4x4 offroad guys. That's the best place to start if you're calling around looking for a shop, the 4x4 guys do differential work ALL the time. There's nothing special or magical about the FD diff, it goes together and sets up like most any other diff out there.

At some point I wouldn't mind setting a diff up myself, but there is a bit of a learning curve involved and getting over that for me might mean a few pulls and re-installs of the diff, paying a nominal fee to have a pro do it is worthwhile. Also, you really need a hydraulic press and a few other specialty tools to do it right.

Dale

 

Thanks for posting this. Seems like I go to one of the local U-PULL-IT lots for one thing or another anyway...I'll have to keep my eye out for an 8.

 

Awesome. Dale strikes again

 

You should notice the performance, and the overall feel being very different. I had changed the gears in my 5.0L mustang and it was drastic. I went from stock 273 to 373 though. First gear was almost useless because it would spin so easily.

 

http://www.ebay.com/itm/Ring-And-Pin...#ht_787wt_1270

For people interested.

 

Hmmmm.

Lewis&Clark, Dale Clark...... coincidence?

 

I'm liking the RX-8 diff cover. Nice touch and great information thank you.

 

whats the nubbin on the side supposed to do? It's like an odd cooling wing or something? I can't really see it doing much, but the new one is cleaner

 

 

I'm believing it's a heatsink out in the airflow to help shed heat. Again, I don't think I'm in danger of overheating my diff, but it's just cool. Too bad you can't see it under the car.

Of course, next DGRR car show I'll jack up the car and put mirrors underneath. And I'll get a mural of Elvis with Rich's head on the hood.

Dale

 

I havent had chance to compare yet, but whole assembly is not interchangeable, right?

 

Nope, I checked myself. The diff housings look similar, but how the powerplant frame attaches is TOTALLY different. You'd be WAY ahead just swapping the ring and pinion.

Been driving the car for a while now with the 4.44's, been VERY pleased. Really gives more response off the line and the car feels way more "eager". The RX-8 diff cover has been fine, no problems, no leaks, no interference issues.

Dale

 

The cover is a great find with eth extar cooling fins. So not interferance problems with the longer upper fins? As I have a Chadwick 2in1 Diff Brace on order looks like fit up mods will require cut off of the cooling fin appendice.

 

Julian -

If that is the case wonder if Chadwick could deliver a design that would allow for the RX8 fin if there is enough demand?

 

Thanks for the info!

 

good to know, i have an 8 differential sitting in the shop that doesn't have a home.

 

For those who did the RX-8 r/p swap, did the old shims swap in as well? I ask because I did the swap a few years ago with all new bearings and seals, and my diff started to make a noise a few thousand miles later.

 

If it's making noise, you either had a bearing that got some trash in it or the preload wasn't set up right. The shims are about as low tech as they come, that wouldn't cause noise issues.

Mine's been just fine, I had it all professionally installed. Our diffs aren't weird or different, they're pretty standard as far as diffs are concerned.

Dale

 

Thanks for sharing the info!
Does this swap throw the speedo out and if so, how to calibrate so it reads right again?