I'm wanting to change my s6 diff ratio for something between 3.0 and 3.30. Will any other crown wheel and pinions bolt strainght in from another type or make of car?

Will a s4 or s5 diff fit up to s6 axles (same spline). I am making the diff mounts to suit my car.

 

RX-8 Ring and pinions are interchangeable.

 

holy cow..... thats a long final drive ratio!!!

 

True but the long ratios can be countered by higher gearing in the tranny. Long drive axles like that tend to be very stout because you have more metal in the gear itself with less teeth to break. The Supra runs a rear end in the low 3's also. That combination has always made me wonder if that's the reason their trannys always hold up to hi HP? I can see how the tranny would hold up better with higher ratios if you put more of the load on the larger gear of the rear end instead the smaller gears in the tranny. With the Fd it's the opposite. You have a higher ratio in the back and longer gears in the tranny.

My theory may be completely wrong so who knows. Anyways here's the Supra gear ratios to compare

1998 Toyota Supra Turbo
6 Speed Manual
Final Drive 3.27:1
1st Gear Ratio 3.83:1
2nd Gear Ratio 2.36:1
3rd Gear Ratio 1.69:1
4th Gear Ratio 1.31:1
5th Gear Ratio 1:1
6th Gear Ratio 0.79:1
Tire diameter 25.03"

1993 Mazda Rx7
5 Speed Manual
Final drive 4.10
1st Gear Ratio 3.483
2nd Gear Ratio 2.015
3rd gear Ratio 1.391
4th Gear Ratio 1.000
5th gear Ratio .719
Tire Diameter 24.86"

As you can see gear for gear the Supra gears are higher ratio even though it's a 6 speed yet you get more mph for each gear because of the taller rear diff ratio.

Road Speed for each gear at 3,000 Rpm's

Supra
18,29,40,52,62,86

Rx7
16,27,39,54,75

 

there might be a 929/mpv/pickup ring and pinion that works.

stock FD is 3.9 for the auto, 4.10 for the manual, and 4.3 for the cool cars we didn't get...

the rx8 gears fit too, but these are 4.3, 4.44 and 4.77....

 

keep in mind the supra's engine hp peaks at 5600 rpm which is alot lower than the rx7, this may account for alot of the reasoning for such a difference in rear end ratios.

 

Im using this diff in a kitcar. This will be connected to a 1000cc motorbike.

 

With a FD diff weighing around 36kg, without fluids, seems a strange choice for your application.

Some of the 70s fuel crisis diffs had low 3.xx ratios if you're committed to Mazda and you can get a salisbury style lsd for them fairly easily.....housing it for IRS might be more tricky.

KIA has some cwp that interchange with early (short) Mazda, if you want to search ratios. Some of the lotus clones here use those smaller - live - Mazda rear ends without issue.....and somewhat more than the 80 ft/lb you'll be putting out. BTW, typical torsen chain drive diff ranges from about 7 to 9kg - can see why you wouldn't want to live with the chain though.