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Discussion Starter #1
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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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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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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Discussion Starter #4
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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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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3.9 would be

100kmh @ 2500rpm
120kmh @ 3000rpm

This is for a tyre diamer of 645mm.
 

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Discussion Starter #8
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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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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I had t5 manual in el six and 4.11:1 gears about 2600rpm @100kph. If i went back i'd go the 3.7:1 better overall/nice combo for drivability and pace of the mark. Life was a lil hard when trying to put power down off the line and for every 3 gear changes i made my mate only made 2. When i put the s/c on the EL 1st gear was useless! Some of the Hsv's use 3.7's to get thier big guns moving down low.
u now have a ute and 3:45 diff is nice but i also have a 3 speed auto built to take a thumping. I'd love a fourth gear and 3:7's.

Look at the yanks and the number of 3.7 diff ugrades that are a standard part of moding thier mustangs for street thumpers
 

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3.9 would be

100kmh @ 2500rpm
120kmh @ 3000rpm

This is for a tyre diamer of 645mm.
i dont know what diameter my wheels are, but its only about 2200 to 2300rpm @100 with 3.9s

first gear is very short, but i believe it will complement my new engine/computer combo (AU I6 with about a 6/6200rpm redline and MAF sensored computer).

if i was ever going to turbo it i would put a set of 3.45s or maybe even 3.27s in - 3.9s are way too short for a very high hp application.

also - having an XR6 some people think that i have a shorter first gear ratio in the box, and a taller 5th gear??? i dont know if that is true or not though.
 

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Discussion Starter #13
well, not real happy, ended up with 3.08 gears which i didnt want but this guy put em in anyway. i fully told him i wanted at least 3.45 and but 3.7 if he could get some. so i would have been better to stay with old ones which would have only been $480 instead of $660 with no real difference. anyway what can i do now>? i wish he had to pull it all back out. oh and by the way, the hemishepre did have to be replaced, well thats what he said, he probly didnt.
anyway sorry for wastin time askin opinions
 

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2.92 to 3.08 is really not worth the effort, go back and complain like a wild man, tell them you will be going to another shop to get the work confirmed the gear you asked for and they will be billed for it, see what they say, tell them you want half your money back and you are not happy :0)

Jason
 

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Can't follow your pricing. What exactly was done, what was replaced, and what did it cost?
 

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Discussion Starter #16
i may as well go back ay, nothin to lose now.
anyway he replace the old 2.92 gears with 3.08, he also said i had 25 spline axles and replaced them with 28, and he showed me the pinion he says he took out and it has 2 wheels, whereas the one he said he put bak had more?? new bearings from wheel 2 wheel. this is only what he told me, he probly didnt now i think about it. total cost was 600+gst=660
im not sure he did anything tho, ive done 320kms on it and no difference at all except the klunk has gone
 

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He has basically upgraded your EA? diff to an EB one. Did he change the speedo gear in the gearbox?
 

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falcon_boy said:
yeah pretty much.

he didnt mention the gearbox so i suppose not. what does that do?

speedo may not be as correct its the speedo gearing that changes the speedo on the dash theres different cobinations depending on diff and tire profiles/sizes.

2.92 diff = 19 teeth yours may be closer to 20/21teeth.
 

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Here is what the ratio change I did to my car, excuse the repost for those who have read this some time back:

I've got an EB XR8 (MANUAL), original ratios = 3.27:1, now with 3.73:1. Here's a quick run down on how the ratio swaps will affect a car with this combo. My original stats were:
(4th) 60km = 1500
(4th) 80km = 2100
(4th) 100km = 2600
(5th) 80km = 1500
(5th) 100km = 1900
(5th) 110km = 2100

now with changing ratios to the following:
3.45 -(4th) 100km = 2745, (5th) 100km = 2025
3.73 -(4th) 100km = 2972, (5th) 100km = 2220
3.91 -(4th) 100km = 3157, (5th) 100km = 2683
( thats with 16inch - 225/50 rubber all round)

according to the diff guys, a general rule of thumb:

3.27 to 3.45: add 125revs (5th/100)
add 145revs (4th/100)

3.27 to 3.73: add 320revs (5th/100)
add 372revs (4th/100)

All round the car is more useable - better power delivery throughout the range & as far as economy goes, it suffered a little, mainly because you tend to drive it harder but otherwise normal driving (city) - no change.
 
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