Hey guys,

I want to change the ratio in my R200 for the drag strip. Current ratio is 3.9:1 and it has a clutch type centre which I think is a Nismo aftermarket thing.

It's in a 1600 with an FJ20et & GM Trimatic combo. The trimatic ratio is pretty tall so I want to change to a 4.1 or 4.4 diff ratio to help with acceleration and get it up on boost a bit quicker, turbo is a GT3540R, so its as laggy as with these ratios. (Boost comes on around 4500rpm )

Can these things be changed out with a simple pinion and crown wheel change? Or is there more too it because of the centre?

Any help appreciated,
Blayne

Yes. You have to make sure you have long nose ratio though, as the short nose have a smaller pinion shaft length and different ratio between the CW&P. (finer teeth)
Suggest you also check what Crown Wheel bolt dia. you have. Some have 10mm and some have 12. Some centres suit both!

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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#SR20Datsun @SR20Datsun

sort of related.
do you guys think a 4.44 ratio diff is too low for a road car?
on my sr it'd make it about 3400 rpm at 110km/h?

For a road car I'd go a 3.7.
Depends on what you want to do and what kind of power you have.
The 3.9 I have is a good all rounder for street and track.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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#SR20Datsun @SR20Datsun

4.4 would be fine on the street. Its the factory ratio in HR31's.
Depends how often you drive on 110kph roads tho.
I had a Z31 4.6 with fj20t and it was great acceleration but a bit revvy >100kph. I never drove it on freeways much so wasnt an issue.
Non datsun related but fyi i just changed the diff in my v8 calais from 3.1 to 3.9 and its fine on the street too. A 4cyl revs more than a v8 so a ratio like 4.1 or 4.4 will be ok...

Nick, HR31's need to rev because of the rev happy RB20DET which had nothing down low and fun up top. Plus a rev limit upwards of 8.5k rpm...
SR20's came out with 3.7's all the way to 4.1's if you were Japanese!
We are talking about a road car, so cruising at 100km/h is a necessity!

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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#SR20Datsun @SR20Datsun

A while back I swapped the diff in my daily RX-7 from the standard 3.9 for a 4.11, and to be honest barely noticed the difference. I don't know exactly what ratios are available in R200s but I'd suggest you'd be better going for a 4.3 or above if you actually want something noticeable. Bear in mind that your gearbox ratios and rolling diameter of your wheels will also change how the car feels. Might be worth looking into as well.

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green200b - aka Alistair

The fleet:

Australia:
'80 200B GX - the green200b - hibernating
'81 RX-7 - 12A extend port - daily
'74 RX-2 - 13B bridgeport - cruiser

Europe:
'93 200SX - CA18DET - tourer

with the online calculations, my car will rev at 3300 at 110kp/h. with the big wheels.
I'm tempted by it. it would be 2900rpm for a 3.9ratio. notmuch difference. combination of street and track.
would rev about the same as my Subaru.

Considering most cars in 5th rev around 2300 or less doing 100, it sounds like a big difference!
End of the day it's your fuel I do like the responsiveness of going a higher ratio like a 4.1 or 4.4.
IMHO the perfect all round is a 3.9 but that's just me

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

depends on if it's a 4 or 6. my Subaru is 3500 at 118 from factory... exactly the same. but that difference is in the gearbox over diff.