Diff Ratios for Longer Gearing?

[Tosseef Hussain]

How does everybody get longer gearing for top end on their 13? What are the stock diff ratios and will Skyline diffs have longer gearing on theirs?

Car is stage 3 CA. I ask cos mine is a touch high on the RPM's in 5th.

[alanjuggler]

skylines are fairly short generally - shorter than the UK S13, if you want lower, find an S14 manual diff.

http://www.nicoclub.com/Greg/ratios.html

http://hardtuned.net/forums/index.php?showtopic=337751

the best list is in the scan from the japanese magazine.

[Tosseef Hussain]

OK, So mine is 4.3. Do I want higher or lower numbering?

[alanjuggler]

got to be careful reading the lists - doesn't cover european S13s, they're 3.9xx. that's what your current one will be.

[Sidewaysfun]

ASAIK the lower the number, the longer the gearing, ie the higher top speed right?

[Christian]

Use the diff off a S14 manual, this is what I did.

It now does around 110 km/h in 2nd and cruises 160 in 5th with about 4200 Rpm

[immy21]

4.3 turns of the prop to turn the driveshafts once
3.9 turns of the prop to turn the driveshafts once, so if you turn this 4.3 times, you will end up slightly further down the road than ^^

Lower number = taller gearing

[alanjuggler]

yeah, exactly - i'm using a 4.083 diff and with an OSG box, I'm at 155mph at 7000rpm. with the 3.916, it'd be 162mph. S14 diff would be 172.

[M.D.]

your diff is not a stock s13 diff if its a 4.4:1, the stock s13 diff is a 3.9:1 and its far far too long for anything below 400 bhp imo. the 4.4:1 that you have now is what i have in mine and imo its a perfect ratio for the s13, it will still cruise at 70 below 4krpm and ive still had 30mpg from mine on occasion.

i removed the stock 3.9:1 and fitted the diff you have now and the car wend from being all slow and lethargic to a snappy fun car which does really well point to point now.

granted the car on a run feels more ''buzzy'' but then it still sits at less rpm at 70 than my totally stock civic type r does. unless your going for a top speed car, which at stage 3 it wont be anyway its only going to make the car feel slower with the longer diff fitted.

[skyshack]

It reduces top gear response at M-way cruise. Legal speeds will be further off boost, lack of response will require more frequent gear changes.

If you have fitted a bigger turbo then its already moved the boost further up the rpm range. It has deficit on stock upto 65mph and longer gearing will move that up 73mph. Longer gearing puts the additional power out of legal speeds. Below 133mph you should be in 4th. It also means it's as lame up 65mph as an Alfa JTD. Though not as poor as a Corvette in 1600rpm at 70mph 6th - it's only truly awesome in 4th or lower.

You will find very few opportunities to use max speed, so gear down, accept the slight increase in harshness of a higher rpm and restore the 60mph top gear performance. It will use more fuel. Also remember that best performance is not the rising part of the accel curve (that's just for M-way cruise to get to the trackday) but on the falling part of the curve, above peak torque.