Diff Swap For Rb30det?

[Alf]

Compression plays an important part.

For the street 3.7's seem to be perfect with 9:1 comp. Anyone with 4.3s must have balls of steel as in the wet traction is a joke.

Comparing top speeds in 5th gear is irrelevant, like anyone would be that stoopid on the street.

Edited January 7, 2009 by Alf

[MBS206]

  Alf said:

Compression plays an important part.

For the street 3.7's seem to be perfect with 9:1 comp. Anyone with 4.3s must have balls of steel as in the wet traction is a joke.

Comparing top speeds in 5th gear is irrelevant, like anyone would be that stoopid on the street.

4.3's here...

1/4 Throttle + Wet + Rolling at 80 KM/H = Needing two lanes of the road...

[psi]

4.3? mine is 4.1. Well thats what the compliance plate says.

My Freinds S2 Stagea (Auto) has a 4.0 according to the plate..

I had the diff apart the other day and it never accured to me to count the teeth!

I was looking at something around the 3.6~3.7 area. The humble old VL had 3.45 and the R31 had 3.7.

If that is what the factory did, then perhaps I may follow their lead..

I have 2 diffs, so if I don't like the out come, I can always swap it back! lol.

[MBS206]

  psi said:

4.3? mine is 4.1. Well thats what the compliance plate says.

My Freinds S2 Stagea (Auto) has a 4.0 according to the plate..

I had the diff apart the other day and it never accured to me to count the teeth!

I was looking at something around the 3.6~3.7 area. The humble old VL had 3.45 and the R31 had 3.7.

If that is what the factory did, then perhaps I may follow their lead..

I have 2 diffs, so if I don't like the out come, I can always swap it back! lol.

Check what the other gear ratios are in the gearbox on the VL and the R31 first, calculate what the final end ratio would be and make sure with your gearbox, and your new chosen diff, you'll get the same final end ratio.

[Guilt-Toy]

i just want to change the 5th gear ratio in my gearbox to drop the revs a extra 1000rpm lower. Then i would be happy. but apparently this cannot be done.

right?

[brent32]

great thread guys, i was wondering about the pros and cons of a diff swap.

sounds like its not worth the time and effort.

Anyway even if you cant cruise at highway speeds without reving to 3000-4000 you can still accelerate in 5th in a 70 zone, try that in a RB20.

also has anyone got any idea what the top speed of a R32 gtst with a rb25 gearbox would be im guessing about 220 reving to 6500-7000 on 18s

[bubba]

R32 GTSt, RB30DET, RB25DET gearbox, 3.9:1 final drive on 245/45/17s: 100kmh in 5th = 2500rpm, pulls up big hills @ 2000rpm in 5th.

I found my ratio change totally worth it

Edited January 12, 2009 by bubba

[MBS206]

  brent32 said:

great thread guys, i was wondering about the pros and cons of a diff swap.

sounds like its not worth the time and effort.

Anyway even if you cant cruise at highway speeds without reving to 3000-4000 you can still accelerate in 5th in a 70 zone, try that in a RB20.

also has anyone got any idea what the top speed of a R32 gtst with a rb25 gearbox would be im guessing about 220 reving to 6500-7000 on 18s

Should be ~240 - 250km/h. But it's ridiculous to want to get to those speeds anyway

[Alf]

This excel file seems accurate for calculating revs and speed.

rev speed calcs -excel

[brent32]

  MBS206 said:

Should be ~240 - 250km/h. But it's ridiculous to want to get to those speeds anyway

at a amateur style track day i did at hidden valley in darwin 220 was possible with standard gearbox and modified rb20, also when i lived in the territory it was 'technically' legal on some public roads. Having said that i sincerely agree that on a public road it is stupid and dangerous to travel at excessive speed.

[MicK51]

i too have a 32gtst with rb30/25 combo, currently i have the factory 4.11 diff but am having to change into 5th down the 1/4 which is a pain.

i've been considering going to 3.9 and my tuner agrees, the alternative would be using a taller tyre at the drags (set of micky thompson et's would be nice )

what gear r u finishing in down the 1/4 bubba?

[bubba]

Factory for 32gtst is 4.363 or something

Umm, across the line is about 6500rpm in 4th

[MBS206]

Bubba, what time, MPH, and RWHP are you running?

[psi]

Hey Bubba, what did you pull the diff out of?

Were you able to take the speedo drive as well?

You also said that the car pulls from 2000rpm, what turbo?

cheers

[bubba]

  MBS206 said:

Bubba, what time, MPH, and RWHP are you running?

Of two runs, best was:

13.9 @ 103mph, 2.3 60' (zip traction in 1st), ~250rwhp (@~4600rpm)

Crossing the line at ~6500rpm is well into my nopower zone (turbo falls over at 5800rpm and at 6800rpm limiter it's making 90rwhp ), figured changing into 5th that close to the line was a waste of time though.

  psi said:

Hey Bubba, what did you pull the diff out of?

Were you able to take the speedo drive as well?

You also said that the car pulls from 2000rpm, what turbo?

cheers

Auto S13.

I used a whole untouched Navara drive (as I was putting a 25t box in aswell) and the 17T cog that comes attached worked out pretty well, speedo reads 7kmh high.. not bad

Edit: guess that sucks if you have a 33 but I guess you could do the reverse of what the 32 guys do and graft the Navara cog onto your sender!

Turbo is the series 1 RB25 turbo that I had on my RB20.. 12psi by 2200rpm

Edited January 14, 2009 by bubba

[bubba]

  bubba said:

R32 GTSt, RB30DET, RB25DET gearbox, 3.9:1 final drive on 245/45/17s: 100kmh in 5th = 2500rpm, pulls up big hills @ 2000rpm in 5th.

I found my ratio change totally worth it

My bad, realised last night that 100kmh in 5th = ~2250rpm (as read from the ecu.. tacho is a couple of hundred rpm out)

[psi]

not that it really bothers me, but did you do the diff swap after your RB30det was installed?

I'm wondering if you can give some feedback as to the difference in the gearing on the road, and how the 'feel' changed..?

cheers

[bubba]

Yeah I did it after the 30 went in.

4.3's were very "brutal" with my setup.. with it making it's power so early and falling over at 5800rpm it was rather violent acceleration with too many gear changes (would also spin 3rd in the dry, something I can't get it to do with the 3.9s now even with shitty tyres, on a track obviously ). With the 3.9s it's not as neck-snapping, gave me some speed back in each gear but most importantly it made it a lot NICER to drive and makes more use of the abundance of torque.

When I first changed, it was very noticable but now it's just normal as far as I'm concerned

I will be interested to see how the taller gears go with the new turbo when I actually have some lag again.. might be a different story..

[brent32]

  bubba said:

6500rpm is well into my nopower zone (turbo falls over at 5800rpm and at 6800rpm limiter it's making 90rwhp )

having the power peak lower in the rev range must make the diff ratio feel even more out of sync.

With the VCT head and a small turbo (on my car) the power band is pretty broad i would say its usable from 2500 to 7000, even though my dyno results say 5000 is the peak power it doesnt feel bad revving to 7000 because it doesn t drop off that much(280rwhp peak-220rwhp redline).

Do you think going for a bigger turbo will make your power band match your ratios better? or just make you want to change ratios again.

Edited January 17, 2009 by brent32

[bubba]

Doesn't feel out of sync at all, I usually only rev to 5500rpm so the ratios work pretty well with the current setup. Have had the 30 with the small turbo and the 3.9's for over a year now and it's great.

As for the ratios and the bigger turbo, only time will tell! I have my old diff here if I need to change back.. I shouldn't think I'll have much problem spooling the GT35R up so hopefully the 3.9's just make for bigger burnouts