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R34 Diff Ratio's

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Abo Bob
Abo Bob

For every 1000rpm at 1:1 gearbox ratio, so 3rd gear in an auto or 4th in a manual, with a 4.083 diff (I found the figure, last time was off the top of my head), you do 29.7km/h by my calculations. Th

admS15
admS15

20 inch rim and 35 profile tyre is the problem there, not enough tyre wall, not to mention a good quality 20 inch tyre would be big $. An 18 inch wheel with 245/45/18 woul be heaps better.

Adz #24
Adz #24

Already had a decent set of 245/45/18 wrapped on Rays and was facing this problem plus the added fact that my clearance was horrible and I ruined my front bumper therefore the move to the larger wheel

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TokyoTaxi Veteran

TokyoTaxi

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Thanks Dan. You would'nt happen to know if an R34 diff ( non GT-R ) is the same as R33 GTS-t in fitment ?

What I want to do is put a lower ratio diff in my car to get more out of the revs ( especially on the Freeway ).

The GTT - Auto - RC40 - 4.0 : 1 diff might be just what I need.

Really need to find out my diff ratio now :)

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  • 2 months later...
dori34 Grand Master

dori34

Posted
Posted (edited)

what centre can i use to put it in a r34 25GT ?

atm mines only a single spinner so i want a lsd that spins both wheels.

would a r33 gtst diff centre fit?

what about a S14 or S15 one?

can i just shim up the standard centre i have now ?

Edited by dori32
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Abo Bob Grand Master

Abo Bob

Posted
Posted

Some info:

GTT auto diff is 4.089:1, manual is 4.111:1. The difference is unnoticeable.

I put the diff centre from an R33 into my GTT and it bolted in perfect. We looked at doing the housing but it didn't look like it would fit, although I think the one we had was a non ABS R33 so perhaps that was the reason.

I bolted an R32 GTR diff, housing and all into my GTT. The traction control stopped working but I didn't care. The ABS still works.

Scott, if you're still looking, I can ask Dan if he still has my old 4.089 centre lying around. I left it at his place as that's where we did one of the swaps. It single spins when hot but with no turbo this may not matter and would be free. Otherwise, anyone who has put a mechanical centre in an R33 or R34 GTT will have their old worthless centre lying around which you could use.

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TokyoTaxi Veteran

TokyoTaxi

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Some info:

GTT auto diff is 4.089:1, manual is 4.111:1. The difference is unnoticeable.

I put the diff centre from an R33 into my GTT and it bolted in perfect. We looked at doing the housing but it didn't look like it would fit, although I think the one we had was a non ABS R33 so perhaps that was the reason.

I bolted an R32 GTR diff, housing and all into my GTT. The traction control stopped working but I didn't care. The ABS still works.

Scott, if you're still looking, I can ask Dan if he still has my old 4.089 centre lying around. I left it at his place as that's where we did one of the swaps. It single spins when hot but with no turbo this may not matter and would be free. Otherwise, anyone who has put a mechanical centre in an R33 or R34 GTT will have their old worthless centre lying around which you could use.

Cheers for the heads up. It's sort of a project on the slow boil atm.

First thing I'm pondering is what sort of speedo error will result if I change from a 4.3 ratio to a 4.0 ?

Who's good with maths ?? :P

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Abo Bob Grand Master

Abo Bob

Posted
Posted

For every 1000rpm at 1:1 gearbox ratio, so 3rd gear in an auto or 4th in a manual, with a 4.083 diff (I found the figure, last time was off the top of my head), you do 29.7km/h by my calculations. This is 3370 rpm at 100km/h.

With a 4.3 diff it's 28.1 so 3560 rpm at 100km/h.

So a drop of nearly 200rpm with the different ratio.

I think this is 5.3% out on the speedo so if it shows 105 then it's actually 100 and since it's likely without the diff change to be doing 102-103 when showing 105 already, there's only about 2km/h for you to worry about when Mr Plod looms over the horizon.

*It's early in the morning so I may have stuffed something up but it sounds right.

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  • 2 years later...
bra0063 Collaborator

bra0063

Posted
Posted

hi guys im also interested in changing my NA r34 gt coupe's diff ratio i looked at the firewall plate and it said ive got a RC40.

i looked up and someone said they should have an RC43?

does anyone know where i can get a diff with different ratios to it will be more responsive?

and also any info about shift kits for auto's as well in victoria.

cheers.

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bra0063 Collaborator

bra0063

Posted
Posted

hi guys im also interested in changing my NA r34 gt coupe's diff ratio i looked at the firewall plate and it said ive got a RC40.

i looked up and someone said they should have an RC43?

does anyone know where i can get a diff with different ratios to it will be more responsive?

and also any info about shift kits for auto's as well in victoria.

cheers.

why are the stock diff ratios so high also?

is it even possible to make them higher?

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  • 2 years later...
GTSBoy Grand Master

GTSBoy

Posted
Posted

hey guys reviving this thread, so do all r34 25gt 4 door autos come with a final drive ratio of 4.363 in the diff?

Hard to say. See bottom of page 3 for confusion.

http://www.nismo.co.jp/en/products/competition/lsd/pdf/lsd_price.pdf

You can see 2WD R34 NA autos have both the 4.083 and 4.363 diffs. But if you look really closely you'll see that NA cars with a viscous LSD have the 4.083 ratio and the cars with open diffs came with either.

This table is supposed to be accurate, but in reality, the number of R34 (GTT) helical LSD cars that actually appear to have been made is close to zero, despite being in the table. They exist, that's why they're in the table. On the same basis, there might be very few or almost none of the RB25DE autos with the 4.083 ratio. Or there could be lots. I don't know.

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  • 4 years later...
Adz #24 Explorer

Adz #24

Posted
Posted

Reviving this thread. My GTT was originally auto and was also converted to manual in Japan, it states that I have the RC40 but how I can check to see whether this is still the case. Also if it hasn’t been change previously and still is the RC40 what would be the best option keep it as is or change it for something else.

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KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted
3 hours ago, Adz #24 said:

Reviving this thread. My GTT was originally auto and was also converted to manual in Japan, it states that I have the RC40 but how I can check to see whether this is still the case. Also if it hasn’t been change previously and still is the RC40 what would be the best option keep it as is or change it for something else.

If you don't have a reason to change the ratio then leave it alone until you think of one.  If you are going to double the power you may want to get an LSD but not necessarily change the ratio.

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GTSBoy Grand Master

GTSBoy

Posted
Posted

Why change from 4.083 to 4.11?  Makes no sense.  You will never tell the difference.

As to the LSD.....The Nismos are broadly considered to be the nicest.  1.5 way for the street.  2 way for hardcore carpark action.  After that, Cusco, etc etc, are all rather similar.  Some have different features (like being able to alter the config from 1 to 1.5 to 2 way).  Some are really harsh to live with but can be moderated a little with different oils.  Have a read on here for mentions.

If I was to replace my helical, I would probably go Nismo.

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  • 4 weeks later...
Adz #24 Explorer

Adz #24

Posted
Posted
On 7/27/2018 at 8:14 PM, GTSBoy said:

Why change from 4.083 to 4.11?  Makes no sense.  You will never tell the difference.

As to the LSD.....The Nismos are broadly considered to be the nicest.  1.5 way for the street.  2 way for hardcore carpark action.  After that, Cusco, etc etc, are all rather similar.  Some have different features (like being able to alter the config from 1 to 1.5 to 2 way).  Some are really harsh to live with but can be moderated a little with different oils.  Have a read on here for mentions.

If I was to replace my helical, I would probably go Nismo.

Thanks for the info.

The issue I’m having with my r34 gtt sedan that has no major engine mods that was converted to manual in Japan is that I’m losing traction way to easily in 1st and sometimes in 2nd, (powers just not making it to the ground properly). I’m moving to a wider wheel setup so hopefully this reduces the loss of traction a bit but if not I’m thinking the next option is changing/upgrading the diff.

It’s my daily driver so 1.5 way would be where I’d want to go. Would a vspec GTR diff be an option?

As you can probably tell I’m new to this so slowly learning my way around things.

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