Newbie questions, other than Ford 7.5 & 8.8 rear end...
 

Other than Ford 7.5 & 8.8 rear end, what other rear end can miata use?

Other than that, how-come the 8.8 set up seems to be the most common one?
what is the advantage & disadvantage of this set up?

So far, what I understand is you need to put a set of un-equal length drive shaft at the back, why is that a good thing?

secondly, is that rear end usually come with a set of LSD, and that's why it's so popular?


thanks

I used the gertrag diff with 3.72 gears and it used equal length half shafts. The only down side is that it isn't well suited for drag racing as it is not as robust. I've had mine for 2 year and about 3500 miles without problems
Tom

Hey

sorry to get back so late.

May I ask, why you pick gertrag diff at the beggining instead of a one?

Super Turbo
GROUND CLEARANCE !!!!!
and I'm not a drag racer, I prefer the corners. So you can add (remove) weight to the list.
Tom

I use a RX7 turbo 2 with a 3.72 gear, just hope it will hold my 5.0l power...

As mentioned above, the RX7 and Getrag diffs can be used. The Ford just seems to be more popular because the original Monster Miata used it. Also the present day Monster kits are designed around the 7.5. And there are probably several hundred of those cars in existence. So there's a big experience base.

Back in the day, before GM popularized IRS rear wheel drive cars, the TBird/Cougar of the early 90's came with a US made IRS diff, either 7.5 or 8.8, and it was widely available. They are still prolific, therefore cheap, in the junkyards, and many come with limited slip, especially the V8's, and the 8.8 was found behind the V8 cars and the Supercoupes. The Corvette IRS used a different design that didn't translate to the Miata well.

The Tbird axle shafts are the same length from side to side; they are too long for a Miata, but Factory Five Racing offers the 8.8 in their Cobra replica cars, and have the correct length (shorter) axles available from their parts department. Or at least they used to.

So, the advantage of the setup is that its cheap, readily available, and plenty strong. The disadvantage, especially regarding the 8.8, is that there is a perception that its size compromises exhaust room somewhat. Most of that perception has been caused by installations that have the rear end mounted too low; the diff needs to be mounted as high as possible.

Mike

Cool post Mike!

Did you have some info with swap done with a rx7 diff like mine?

Thanks.

No, the only info I have deals with the Ford 8.8. I remember that it has been done, I think it was pretty much a bolt in deal, but as I recall the available gear ratios were still pretty low for a V8.

Mike

I used the 8.8 from a 90 T-bird and it had 3:26 posi gears in it. It needs alot more to race it on the strip. The 8.8 really requires adjustable coilover shocks turned up pretty high to get some good clearance back there.

Yes the RX7 turbo II are not the best gear for a v8. There the info i got when i did mine.

4.3:1=43/10 (43 teeth on ring gear/10 on pinion) (GTUs only)
4.1:1=41/10 (FC manual)
3.909:1=43/11 (FC automatic)
3.727:1=41/11 (combined AT and MT gearing)

The lower you can go it's 3.72. With my 225/45R16 tire it's like i have a mustang with a 4.10 gear.

Just hope it's not too fast for a track car.