3.9 ring and pinion swap

[JRS]

I'm racing an S13 in E Production of the SCCA. I currently own a 4.08, 4.3 and 4.6 differentials. I would like to remove the R&P out of the 4.6 and drop in a 3.9 R&P, if there is one available from a previous Nissan model. (I never use the 4.6) I don't care if the 3.9 R&P came out of an open diff, since the 4.6 has the Nissan Comp clutch type LS in it and I can use that.

[orion]

Infiniti J30 diff is 3.916:1 (47 tooth ring gear, 12 tooth pinion). You want one from a '95-96, so it mates right up to your axles. Edit: It is a VLSD.

The ring gear is thicker, so I would use the J30 case, and swap the clutch-type into that.

The front mounts will be different (rubber isolated, like an S14)...and the rear cover will need to be swapped for your S13 cover.

...

HOWEVER, after typing all that...I just realized that the extra ring gear thickness will make it so you need different length output shafts (or stub axles, whatever you like to call them). The center section of the diff will sit about 10mm off to one side as compared to an S13/S14 diff...so one shafts is longer, and one shorter...to match.

If the Nismo diff you have was for a VLSD..then you can use the J30 output shafts. If it's for an open diff, then the J30 shafts may not work. FYI.

- Brian

[Def]

Some good info there.

I'll add that J30 diff cases are all going to be longer since I seem to recall them having the ABS sensor in the snout like S13s(3 channel ABS instead of 4 channel with the speed sensors mounted on each output shaft).

[juggernaut]

The auto s15 also uses a 3.9xx diff ratio. Manual s15's got the 3.692.

I wouldn't have a clue whether it would fit into your s13....sorry if this information is useless to you.

[Colorado S14]

Did I read correctly that there is difficulty with putting the VLSD from a J30 into a S14 pumpkin? I kinda want to ditch the longer ABS housing that came with My J30.

[logr]

Did I read correctly that there is difficulty with putting the VLSD from a J30 into a S14 pumpkin? I kinda want to ditch the longer ABS housing that came with My J30.

I can trade with you. I have regular ones. I might even have a VLSD in one.

[Matt93SE]

Anybody have a 4.3 R&P they want to get rid of while we have this subject on the table?

[logr]

I have a 4.6 that I built with a clutch that I might consider letting go of. I bought the 4.6 new. The clutch doesn't chatter at all.....................................unless you turn.

[Matt93SE]

I have an S15 HLSD I got from mmdb and a spare housing that's waiting on a R&P to put into it.
Unfortunately a 4.6 is too short for me for the tracks I run. I'm already at 6000rpm in 5th gear at TWS and 6400 in 4th gear in two places at MSRH. The rudimentary math says I'll be at about redline in 5th at TWS and near it at MSRH.

Thanks though.

[JRS]

well, I'm not quite sure what I've learned, but thanks for the responses. I might see if I can pick up a J30 diff and just run the vlsd in a race.

[Def]

I have an S15 HLSD I got from mmdb and a spare housing that's waiting on a R&P to put into it.
Unfortunately a 4.6 is too short for me for the tracks I run. I'm already at 6000rpm in 5th gear at TWS and 6400 in 4th gear in two places at MSRH. The rudimentary math says I'll be at about redline in 5th at TWS and near it at MSRH.

Thanks though.

Yea, a 4.6 would definitely suck for my car at most tracks I can think of, and I'm pretty sure a 4.3 would be a take one step forward then one step back. For every corner I could come off in the powerband a little better(like rattlesnake at MSR-C), I think it'll take an extra shift or cruising at redline for a couple of seconds(it would do this at T1 at Road Atlanta, Big Bend at MSRC etc). I can see how the more horsepower challenged of us might get a big boost from that ratio though.

A 4.3 sure would make a fun street car though.

[Matt93SE]

Yeah, exactly.
I'm still planning on running a built NA KA, and rev it to about 7000 at most. 200ish whp and a 4.3 should put me at redline in 5th at places like TWS, and I can run the Z32 VLSD I have with the 4.08 for longer tracks. even at Daytona with its 5000+ft straights, I only ran out of room when I hit the 120mph speed limiter while drafting a 350Z...

[T-Rex]

Yea, a 4.6 would definitely suck for my car at most tracks I can think of, and I'm pretty sure a 4.3 would be a take one step forward then one step back. For every corner I could come off in the powerband a little better(like rattlesnake at MSR-C), I think it'll take an extra shift or cruising at redline for a couple of seconds(it would do this at T1 at Road Atlanta, Big Bend at MSRC etc). I can see how the more horsepower challenged of us might get a big boost from that ratio though.

A 4.3 sure would make a fun street car though.

The 4.6 worked great on my car at all the tracks. At Road Atlanta it essentially eliminated a shift at turn 3. All of the competitive cars ITA run the 4.6. In truth, I doubt you will notice must change between a 3.9 and a 4.08

[T-Rex]

Yeah, exactly.
I'm still planning on running a built NA KA, and rev it to about 7000 at most. 200ish whp and a 4.3 should put me at redline in 5th at places like TWS, and I can run the Z32 VLSD I have with the 4.08 for longer tracks. even at Daytona with its 5000+ft straights, I only ran out of room when I hit the 120mph speed limiter while drafting a 350Z...

The VLSD wont last long if you are tracking it. Especially if it has a lot of miles on it already. The heat breaks the silicon down and they all eventually become an "Open" diff.

[Def]

The 4.6 worked great on my car at all the tracks. At Road Atlanta it essentially eliminated a shift at turn 3. All of the competitive cars ITA run the 4.6. In truth, I doubt you will notice must change between a 3.9 and a 4.08

Shifting at T3? I was definitely in 4th gear from turn-in to T1 all the way to T7. Just gotta keep up the speed, and this was even on street tires. On R-compounds it'd definitely put the car in the 4th gear range.

Ya gotta keep in mind that with a turbo motor, at 4k RPM you've still got about 280 ft-lbs of TQ at the wheels to play with even with the boost turned down for the track from the usual street levels people run(where there'd be more like 300-310 rwtq).

Shifting to 3rd at RA on the fast corners puts you right up towards redline, where you'd be risking hitting the rev limiter somewhere midcorner, so it's better to just keep it in 4th. T7 and T10A are obviously 3rd gear corners with the stock 4.08. T7 would benefit from a 4.36, but I think the 4.08 felt fine for T10A since I was still having to short shift to 4th before T11/the hill.