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Old 02-06-2004, 18:25   #1 (permalink)
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3.7 / 3.9 anyone?

hey all,
just looking for ppl who might have have had diff gears around 3.7/3.9 :1 ratio
in thier car and what they think. im getting mine overhauled on monday but because it is a 2.92:1 (highway diff) the hemisphere has to be replaced to get up to 3.08 or 3.45 so i may as well go higher. any expirience with these would be helpful,
cheers
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Old 02-06-2004, 19:58   #2 (permalink)
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Re: 3.7 / 3.9 anyone?

i've got 3.7's in my fairlane. i wouldn't recommend it for the daily driver, unless your car has overdrive. my car car also has small tyres 245/50/14's (approx 23 inches tall) and at 120km/h i'm doing about 4 grand. it really depends what you use your car for and what you want it to do.
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Old 02-06-2004, 21:41   #3 (permalink)
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Re: 3.7 / 3.9 anyone?

What engine/gearbox? What sort of driving? You do not have to replace the hemisphere to go from 2.92 to lower ratios. It is 2.77 that has the different offset hemisphere.
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Old 02-07-2004, 01:25   #4 (permalink)
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Re: 3.7 / 3.9 anyone?

well , my cars a 6 cyl eb falcon S. has standard 5 speed b.w. so i take it that 5th is like overdive. also, the guy from the shop said i will have to change hemisphere so maybe he's after my money? he did mention a 3.7 would drive around 100km/h @ about 4000 rpm , so thats worse again. its a daily drivin car so i dunno bout revin it out hard just to get to work n bak. he is recomending 3.23 gears but said its obviously my overall choice. i asked him for worst case scenario he says $600 if everything is replaced, extra 400 for lsd, the other thing he mentioned was 3.7 gears are hard to find and says they only find em in skylines so i dunno? what u think.
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Old 02-07-2004, 05:39   #5 (permalink)
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Re: 3.7 / 3.9 anyone?

5speed and 3.7gears will have you reving at 2400rpm@100kmh and 2850rpm@120kmh.
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Old 02-07-2004, 05:46   #6 (permalink)
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Re: 3.7 / 3.9 anyone?

Walkinshaw - those RPM figures are pretty damn good, cuz Rollin has 3.9's and i no he aint anywhere near 4000rpm at 120k's
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Old 02-07-2004, 05:59   #7 (permalink)
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Re: 3.7 / 3.9 anyone?

3.9 would be

100kmh @ 2500rpm
120kmh @ 3000rpm

This is for a tyre diamer of 645mm.
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Old 02-07-2004, 17:29   #8 (permalink)
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Re: 3.7 / 3.9 anyone?

well, that aint too bad, alot beter than the guy rekons. at the moment my 2.92 does like 1600rpm @ 100km/h. only doin 3500 @ 180km/h, so i dont mind if i lose some top end. he still doesnt have 3.7 gears though and rekons there hard to get, is this true?
should i be goin somewhere else, monday 8 o'clock im booked in so there aint much time
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Old 02-07-2004, 21:39   #9 (permalink)
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Re: 3.7 / 3.9 anyone?

You defineately do not have to change the hemisphere. 3.7 are not hard to get, but I would not recommend them. I would go 3.27 with a std T5, and 3.45 if you have the 3.28 ratio first gear box.
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Old 02-07-2004, 22:29   #10 (permalink)
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Re: 3.7 / 3.9 anyone?

k, cheers for all the help guys, let ya know what happens monday or tuesday.

cheers
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