Nars GSL-SE the 'White Comet'

[scarsofcarma]

Originally Posted by Whizbang

check out the trans diff FAQ

Mazda Miata Gearbox
1st: 3.136
2nd: 1.888
3rd: 1.330
4th: 1.00
5th: 0.814

vs what I'm running right now...

Mazda Rx-7 87-88 13B 6PI (Type M) Gearbox
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: 0.697

and my original GSL-SE transmission...

Mazda Rx-7 84-85 13B (Type M) Gearbox
1st: 3.622
2nd: 2.186
3rd: 1.419
4th: 1.00
5th: 0.807

I agree the Miata gearbox seems like a good bet. Lower 1st and 2nd gears should be better in the mountains and the shorter split between 2nd and 3rd should improve overall driveability. The .814 overdrive should even allow for some acceleration in 5th... hard to say if it could improve overall top speed though. In the past when I've tested top speeds on various cars, the rev-limit in 4th gear is the maximum gear-limited top speed unless you have enough power to overcome all that wind resistance in an overdrive gear. (Or just happen to be driving down a really long steep hill)

Reading up about modifying the miata input shaft got me thinking though... I saw this pic on Mazdatrix and I was wondering if it was possible to use an RX7 input shaft on a miata gearset? That would simplify things a lot.



However, after searching about it, it seems that it has been tried with no success.

Originally Posted by RX7 Club

All right. I made some measurements and tried to assemble a hybrid box today using an RX-7 input shaft and a Miata gearset.

The initial problem is that the diameter of the input gear of the RX-7 shaft is about .100" larger than that of the Miata shaft. I did not measure the diameter of the gear on the counter shaft because I do not have a mic that large. I figured I'd try to put everything together, see what fit and how it all mated. I measured 3 RX-7 shafts and 2 Miata shafts and all the numbers were spot on among the lot.

The tooth count is different between the two input shafts and counter shafts but the pitch appears to be the same because once they are together they mesh very well and the assembly initially rotated very freely.

I assembled the whole front side of the box (1st-4th gears) and everything looked great. The problem occurred after reverse gear was in place and I began to add the OD gear. The OD gears would not go on. There is enough of a side load on the shafts from the diameter difference of the input gears that the clearance is ruined on the backside of the tranny.