Differential Ratios

[sambo]

More info found on the Skylines Australia forum - ratios by vehicle models:

4.900 - C23 Serena SR20DE 4WD Auto

4.636 - C23 Serena SR20DE 4WD Manual, C23 CD20T 4WD

4.375 - R32 RB20DET 4WD, A31 Cerfiro RB20DET 4WD

4.363 - R34 RB25DE 4WD, R34 RB25DE Manual, R34 RB20E, R33 RB25DE 4WD, R33 RB25DET Auto, R33 RB25DE, R32 RB20DET, R32 RB20E,
C35 Laurel RB25DE 4WD Auto, C34 Laurel RB25DE 4WD Auto, C34 Laurel RB25DE Auto, C33 Laurel RB20DE Manual
A31 Cerfiro RB20DET, A31 Cerfiro RB20DE Manual, S13 CA18DET, S13 CA18DE, C23 Serena SR20DE 2WD, C23 Serena CD20T 2WD

4.111 - R34 RB25DET Auto, R33 RB25DET Manual, C35 Laurel RB25DET Auto, C35 Laurel RB20DE Auto, C34 Laurel RB25DET Auto, C34 Laurel RB20DE Auto,
S13 SR20DE (ABS),

4.083 - R34 RB25DE Auto, R33 RB20E, R32 RB20E (ABS), C33 Laurel RB20DE Auto, A31 Cerfiro RB20DE Auto,
S15 SR20DE, S14 SR20DET Manual, S14 SR20DE Manual, S13 SR20DET Manual, S13 SR20DE (ABS), S13 SR20DE

3.916 - S13 SR20DET Auto, S14 SR20DET Auto, S15 SR20DET Auto, A31 Cerfiro RB20E. 5 & 6 bolt

3.692 - S14 SR20DET ADM Manual, S15 SR20DET Manual. 5 & 6 bolt

3.583 - R33 RB25DE Auto, C33 Laurel RB20E Auto

* transmissions as stated, if not listed it means they are available in either Manual or Auto.

Forum Link

[WKB]

Merv,
Now that you have information overload, if you are to the next meeting come grab me I will give you names of two people that have already installed S15 diffs into their cars (4.6ltr quadcam fords) and one who has installed a 3.9:1 (5 ltr windsor).
Warwick, when he had his factory car had a 3.7:1 Silvia installed.
The S15's were installed into R32 frames, into a R33 it is easier.

I still check ebay to pick up a spare and over the last 12months the number of R200 diffs available have decreased, so if do see one grab it even if you aren't ready for it.

Warren

[sambo]

Originally Posted by WKB

The S15's were installed into R32 frames, into a R33 it is easier.

Warren, do you have any more info on the S15-R33 conversion? Eg, diff centre, half shafts, what else... rear diff housing cover?

Thanks

[WKB]

Sambo.

With the rear cover from the R33 attached to the S15 diff it should fit straight into the cradle. On the R32 they had to make metal bushes to replace the rubber bushes as the R32 does not have rubber bushes.
Once in the cradle you will see that the snout of the diff sticks out about 20mm further than the R33 diff due to the position of the speed sensor. If your tailshsft is not yet made no problem as you make it to suit, if it is already made there should be enough freeplay to slide the yoke further into the gearbox(this what they did when the S15 diffs were fitted into the other cobras).
When they tried to swap the drive shafts from the R32 diff to the S15 they found the S15 drive shafts had 1 more spline than the R32 had.
Two ways to fix this are 1. Get axles from a SX200/S15/S14 which should be about the same length as the R33. The R32 conversion didn't use this method due the potential cost of the axles. They went the second way and made an adaptor that went between the S15 drive shaft and R32 axle. There was enough movement in the CV's to fit a 8mm spacer between. This might not be issue if the R33 has the same number of splines on the drive as the S15 has.
Both the cobras that had this conversion were 4.6ltr quad cam fords, one with a T56 and the other with a T45. The outcome was the same, quiter at highway speed, easier to maintain highway speeds , better fuel ecomony and able to us first gear for more effectively.

If you are going to do this mod replace the rubber bushes with metal bushes. Under hard acceleration the rubber ones can be damaged.

Warren

[Aussie Mike]

I'm running 3.91 in my CR. I reckon they work great with the 6 speed box. 3.7 might be better for a torque monster LS2 or LS3 motor but my little 5.7 likes the 3.9 gears.

The 6 speed has a tall first and second gear so they are both very usable with the short diff gears.

The 3.9 gears with the T56 2.66 first gear has you shifting 1st to 2nd at 70KMH @ 6000RPM. That's with 315/35/17 rear tyres which are a bit under 26" tall

Cruising @110 in 6th has you ticking over at a nice economical 1700RPM or 2500RPM in 5th ready for a quick getaway.

The same setup with a T5 sees you shifting to 2nd at about 55KMH @ 6000 RPM

Cruising @110 in 5th has you sitting on 2200RPM with the T5.

The 3.692 or 3.583 might be a better choice with the T5.

Cheers