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Which Diff Ratio?

Started by _timbo_hatch_ , Oct 09 2006 09:46 PM

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8 replies to this topic

#1 _timbo_hatch_

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Posted 09 October 2006 - 09:46 PM

Got a ss torana with a 350 chev, top loader and 9 inch. I am looking at
changing the diff ratio, just not sure what I want to change it to.
It is currently a 2.78, and I am looking for a lot more acceleration.
I was thinking either 3.7 or 3.9. I understand that this will cause my
car to rev a lot higher, but i'm not too concerned, because i'm not
planning on doing too many highway k's. Just wondering will 3.9
be taking it too far. Does anyone know roughly what my car will
rev at, at say 100k's?
Thanks in advance,
Tim

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#2 LS1LX

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Posted 10 October 2006 - 11:09 PM

Go 3.55's, you have a manual it shouldnt need much more gearing.
Cruise will be great and acceleration should be fine.

Everyone loves 3.5's, good ratio for auto's and manuals, not too high not too low, so if you ever want to sell the centre they sell like hotcakes.

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#3 _on the limit_

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Posted 18 October 2006 - 10:05 PM

hi, ive got a lc, 308, top loader, 9 inch, 275x50x15 tyres, had 3.50 gears in it about 2500 rpm @ 100k's now got 3.9's doing about 3000rpm's @ 100 k's.

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#4 ls2lxhatch

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Location:Perth
Car:LX Hatch
Joined: 29-May 06

Posted 18 October 2006 - 10:14 PM

I have written a program that allows you to enter rpm, gearbox ratios, diff ratios and tyre sizes and it will calculate the speed.

If you want a copy then send me an email.

Andy

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#5 _STEVO_

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Posted 18 October 2006 - 10:51 PM

go 4.11 i had them and great fun although it had a 4 speed auto
but i did hwy driving and no dramas

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#6 _devilsadvocate_

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Posted 18 October 2006 - 11:00 PM

Does anyone know roughly what my car will
rev at, at say 100k's?

If you have a tacho now and know what rpm you have at 100k, then divide your new ratio by the old ratio and multiply the revs by that.
ie if you have 2600rpm at 100kmh with the 2.78, then you will have (3.9/2.78) x 3000 = 1.4 x 3000 = 4200rpm