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diff gears but keep top end speed... v6 getrag

old mate

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g'day g'day,

as i am planning to take the ute to the racetrack for some legal fun, i know its underpowered and underbraked but its the only was to have some fun and not go to jail these days, i've decided that before i go, a diff gear swap is in order, along with an lsd centre or mini spool. mini spool is cheaper but its not road legal.

so i'm going to go from the standard 3.08 ratio to something a bit shorter, as using my tyre size (235/45 17 inch) and a 5500rpm rev limit (im not sure what the ecotec revs to, i dont have a tacho =(, theres another job) gives me these theoretical speeds (wont be accurate due to possible clutch slip and ballooning of tyres)

1st: ratio 3.829:1 - 56.53 km/h
2nd: ratio 2.199:1 - 98.44 km/h
3rd: ratio 1.401:1 - 154.51 km/h
4th: ratio 1.000:1 - 216.47 km/h
5th: ratio 0.809:1 - 267.56 km/h

not sure if i did this right, but it should sit at 2055 rpm at 100 km/h in 5th gear..

now i know that the V6 will never get that speed in 5th gear, which is kind of a waste, but i'll still need it to be reasonable for highway driving so was thinking about a 3.55 ratio rear end. speeds are:

1st: ratio 3.829:1 - 49.05 km/h
2nd: ratio 2.199:1 - 85.41 km/h
3rd: ratio 1.401:1 - 134.05 km/h
4th: ratio 1.000:1 - 187.81 km/h
5th: ratio 0.809:1 - 232.14 km/h

and will sit at 2369 rpm at 100 km/h.

would this ratio be a fairly good compromise, if my calculations are in the ballpark, it seems reasonable for the lack of engine power etc.

opinions?

this swap is looking close as i have a nice diff oil leak that needs attention, so might just do it at the same time.
:thumbsup:
 

The1

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give you more pickup, main thing people say is more fuel consumption on the highway.
 

immortality

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it's either 3.45:1 or then 3.73:1 (rear as hens teeth though). i have the 3.45's in the VN. pickup is better and i honestly think it's made stuff all difference to fuel consumption. really depends on how you drive it

can't for the life of me see why holden used the getrag with .80 OD ratio. the old T5 with .72 OD ratio did fine and only did 1800rpm @100km/h.
 

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yeah thats true about the fuel economy, im not too stressed about the economy side THAT much. hmm i read your mega-awesome thread on diffs, am i able to get the diff centre from a 6 cylinder vl (turbo) and fit that to my rear end to get the 3.45:1 ratio?

i suppose that the wreckers will be lucky to have a turbo diff lying around and will probably charge a mint for it though.
 

immortality

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all VL's had the 3.45 ratio except the V8 models which had 3.08's fitted. so yes you could go to the wreckers and get any V6 diff and then use those gears in your diff. you could also fit the entire VL diff into your car but would still need to fit a LSD center and the VL diff is narrower then your diff so it would alter your wheel track width also.
 

old mate

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i'll have to swap the gears over into my rear diff, as i would have to run different offset wheels on the back as they are close to rubbing and scrape when the suspension is bottomed on one side.

i'll hit up the wreckers after my exams and get it done.
 

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just on the throwing a VL diff in the back end, with the extra 40mm what type of tyre widths are possible 275's?
 

old mate

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hmm you'll be still limited on the width inside the wheelarch, i get heaps of rubbing on the inside of the guards with just 235/45's on vt ss wheels. just when one wheel gets compressed heaps on side slopes etc.

just came across a rolled r31 skyline with a manual, might grab the diff out of it. should have looked what ratio it was. hopefully its got the 3.73 ratio gears.. bit shorter than i wanted but hey, beggers cant be choosers :thumbsup:
 

DannyboyDS

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you also need to make sure that if your car has ABS, that whatever diff you use in the rear has ABS sensors built in, unless there is a way of transferring them?
 

speed_freak

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car is as basic as they came. previous owner was cheap. no aircon no abs no irs absoloutley no options whatsoever
 

old mate

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with the 3.73 ratio rear end and using 5500 rpm as max revs will give me..

1st: ratio 3.829:1 - 46.70 km/h
2nd: ratio 2.199:1 - 81.30 km/h
3rd: ratio 1.401:1 - 127.62 km/h
4th: ratio 1.000:1 - 178.80 km/h
5th: ratio 0.809:1 - 221.01 km/h

and 2488 rpm at 100 km/h which is getting up there, but not that bad.

i used some internet calculator, so im not sure how accurate it would be.
 

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yeah i looked at the same type of stuff i dont think its 100%. you also have to count in size of tyres and such. but i used one of those internet calculators and put in all the stock figures of the getrag on 15inch rims and got something completely different to what my car actually says at 100kmph

im thinking of going 3.9's with a spool so im leaving the gas system in for the long drives to save on economy.
 

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yeah i used one where i had to enter all my wheel/tyre info, i think its close to the mark but cant trust it 100%.

3.9's hmm, what gearbox do you have?
 

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same as you, the lovely getrag
 

Vs_ss_gmtank

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with the 3.73 ratio rear end and using 5500 rpm as max revs will give me..

1st: ratio 3.829:1 - 46.70 km/h
2nd: ratio 2.199:1 - 81.30 km/h
3rd: ratio 1.401:1 - 127.62 km/h
4th: ratio 1.000:1 - 178.80 km/h
5th: ratio 0.809:1 - 221.01 km/h

and 2488 rpm at 100 km/h which is getting up there, but not that bad.

i used some internet calculator, so im not sure how accurate it would be.
dont think thats right..
i got 3.7s and 4th gear gets to 200 km/h with 5 speed and 18's
 

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dont think thats right..
i got 3.7s and 4th gear gets to 200 km/h with 5 speed and 18's
yeah you're probably right, but im only running 17's with 235/45's, couldnt imagine a huge difference in diameter between the two.
 

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Vs_ss_gmtank what are you sitting at rpm wise at 100kms, im thinking of doing 3.9's with 18" rims, would love to find out what 3.7's make the car sit at.
 

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what size tyres do you have on your 18's mate?
 

speed_freak

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dont have any yet, i kinda wanna see what type of revs im gonna be sitting at before i invest in them. if i do get any though they will be something like 225/35's
 
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