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ruinned

Lower diff ratio for R34 GTT

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Hey everyone,

I am wanting to look at getting a different diff ratio for my R34 GTT, the reason behind this is, that it is starting to annoy me that if i go out of town i need to take a different car because the skyline sits really high on rpm around 100-120km/h and just chugs way to much fuel.

Started looking around and researching, correct me if i am wrong but the diff i have is 4.11 ? Just wondering if there another diff that i can put in the car with a lower ratio.

i have read that s15 diff will bolt right in, but i think they have a ratio like 3.6 which i think would be to low.

 

what wold my options be ?

 

Cheers in advance :)

 

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Even though you are correct in saying it's a "lower ratio", numerically, in terms of gearing we say that the ratio you want is higher, because the effective gearing is higher - as if you are running in a higher gear.

You can't just swap a (whole) diff to achieve this.  The S15 diff has a number of differences that make it not useable as one piece.  The crownwheel and pinion set from an S15 diff could be swapped onto your diff, giving you the 3.6 or 3.7 or whatever it is.  FWIW, I think this would be a great ratio for an RB25 Neo.

If you don't want to go that far, then you would need to find a 3.9 CW&P set from another R200 diff and bang that in.  Beware that there are a number of different bolt sizes and flange thicknesses that make it difficult to throw just any CW&P onto any other centre.  So this may or may not be an easy task.

The (R34) GTR diff is also a possible source, but is all the way to ~3.54 or something, so you're less likely to want that.  Plus, it brings along other complications.

Whatever you do, you will stuff up your speedo calibration, which might not be fixable.  I have no idea what speedo drive gear options are out there to fix such a change (either for the manual or the auto).

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Ahk, learn something new everyday :).

 

Yeah i just had a look online at a calculator tool for working out engine rpm and speed. and the s15 diff ratio is basically exactly what i want for it. lowers the the rpm just enough.

Cheers for the information :) time to get a s15 diff and swap the bits around.

 

speedo calibration, i might have a way around it as i am building my own digital dash so i will be able to alter results from the ecu to correct them my self.

 

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The speedo works like this:  Speed sender at box sends an AC (actually sawtooth) wave of about +/-1V to the dash.  The dash then converts that to a square wave 0-5V signal to the ECU.

You can buy kits (like from Jaycar) that you can interpose in the signal line from the box to the dash to speed up or slow down the pulse rate, easily enough.  You would do the same in your homemade dash, either to the incoming signal or just to the outgoing signal to the ECU.

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When I looked into this I found that S14/15 have ratios roughly 3.7 or 3.9 .

Also the carrier/crown wheel offset changed between 3.7 and 3.9 , I think the S/R series 4.11 is same as 3.9 .

Then the issue is the stub axles because S series is different to R33/34 . You wouldn't want to go backwards by fitting weaker S series joints and axles . There is a myriad of stubs to suit those VLSD centers and lengths differ to suit the carrier offset and inner joint type .

If serious the way may be to use a S series 3.9 and fit an aftermarket LSD with stub axles to suit your R34 . 

Lastly if you use an S series diff as the basis it'll need to be from an ABS car because I think the nose is slightly longer to fit the pinion speed sensor - something to research .

A .  

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Disco,

Many of those things you said above are the reason I suggested not to change the whole diff, or even the whole centre.  It is made worse by the S15 diffs being helical and so the stubs don't even go close to swapping between HLSDs and VLSDs.  The S chassis ABS is done with a single rear speed sensor on the diff nose, not the pair of code rings on the stub axles like the R chassis.  All in all, it's just too much trouble.

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hi there , i too have a yr 200 gt-t , and my final drive ratio is also crap , as its nowhere near long enuff , and i too would love to simply throw in another diff , but from what ive read so far i cant , so i also need a diff from an s15 ?(im in the uk , so is that a 200sx?) and how do i identify what diff i need from the variants ? id prefer the 3.7 i think , and how can i identify an abs diff (sorry im new to skylines) and then i was gonna get aa nismo 1.5 from nengun cuz it has the correct 5 bolt stubs with the kit  ?would that be ok and all work together ? sorry for the tons of questions

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I've typed many thousands of words on this subject into these forums. You should do some searching, 'coz I'm not inclined to type them all again right now. The answers are here though.

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thanks gts boy , it s just there are so many pages to go thru on this forum i thought it might be easier to just ask again ( sorry gtsboy ) , it would just be nice if someone gave me a parts list to go and buy , and then i could get busy with the tools ,as i still feel a bit unsure as what to get , there is a s14/14a/15 diff on bayi could get at a reasonable price (and it has the abs sensor on the neck and rubber mounts at the front , so it sounds like the right one) , then if i swapped the crown ring and pinion i could then fit the nismo 1.5 lsd kit ? , sorry again for the questions , but there is sooo mucch to search thru im going blind trying to take it all in

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3 minutes ago, ben logan said:

thanks gts boy , it s just there are so many pages to go thru on this forum i thought it might be easier to just ask again ( sorry gtsboy ) , it would just be nice if someone gave me a parts list to go and buy , and then i could get busy with the tools ,as i still feel a bit unsure as what to get , there is a s14/14a/15 diff on bayi could get at a reasonable price (and it has the abs sensor on the neck and rubber mounts at the front , so it sounds like the right one) , then if i swapped the crown ring and pinion i could then fit the nismo 1.5 lsd kit ? , sorry again for the questions , but there is sooo mucch to search thru im going blind trying to take it all in

Ask specific questions on Google:

e.g. "will an S14 diff fit my R34 GT"

"how to get a taller ratio diff for my  R34" etc

etc. You will not get the answer you need straight away but you will be pointed to threads (mainly on SAU) which by the time you have read them you will gather the information you need

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