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Old 11-15-2003, 19:02   #1 (permalink)
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Improving accelleration by changing diff ratio.

I apologise if this has been posted before, but I couldn't find the answers anywhere! Please be patient if my knowledge (or lack thereof) in this area is naive/minimal.

I have a stock ED GLi with auto tranny. I'm trying to improve my accelleration and quarter mile times (0-100km/h and 0-400m). I'm under the impression that the diff ratio is one of the main factors holding back the Falcon's accelleration. I also assume that my ED is standard with a 3.08 single-spinner. Therefore, in a couple of months (wish it was sooner) after some mods (exhaust mainly) I was hoping to get a shorter diff ratio, something like 3.7 or 3.9 and most-likely LSD if it's feasible.

Can anyone confirm how this will affect my accelleration? Approximate times would be of great help, especially if anyone has been in this position. Will it affect my fuel consumption significantly? Will it be unbearable to drive at highway speeds (100-120km/h)?

Finally, what sort of figure should I expect for this type of conversion? As I want to know what I should budget for. Lastly, what were the ratios found in VL/VN/VP/VR and VS Commos?

Cheers.
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Old 11-15-2003, 19:25   #2 (permalink)
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Re: Improving accelleration by changing diff ratio.

It will help you alot with accelleration.

Fuel consumption will be a bit higher due to it reving higher at any given speed...but you get that.

It would rev a bit higher at those speeds but where you've got the 4 speed auto with the taaallllll last gear it shouldnt be a problem.

I wouldnt go over 3.9 gears tho as then it would get a bit high..

Talk to quickcorty about the effects of a diff change as he did his and got some good times.

Costs can vary...some people do it themselves for 200 bucks (price of the diff) but others have paid up to $1000 for a full diff change done by someone else. So shop around for the best price.
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Old 11-16-2003, 23:23   #3 (permalink)
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Re: Improving accelleration by changing diff ratio.

I'm hunting for a center for my EF futura, I will proly go to 3.7

You might want to know that most E series non XR's only have 2.77, my XF had it and my EB Series2 as well as a friends ED.

Some diff shop are complete wankers (scuse my language) when they hear diff gear change they know you want performance and they charge you for it like mad. When you aproach them just thell them that you got a Nissan diff 3.7 or 3.9 and you want the gears put in your ED, that will make them change the song. But if it cost's 1k to do a convesion why bother? get a supra 5 speed and you get more for your 1k (you have to be able to fit it yourself)
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Old 11-17-2003, 01:11   #4 (permalink)
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Re: Improving accelleration by changing diff ratio.

i have a EB XR6, it came with a 3.45LSD and i put in a 3.9LSD from a skyline, and sold my diff to 94ED_Fairmont, who had a 3.08 open diff. my car revs about 250-300rpm higher on the freeway@100, dont know about 94EDs though.

my car gets out of the hole like its been kicked in the ass, and 94s car is also noticably faster - he hasnt lost to a V6 commo since he put the diff in :D

unfortunately i cant give you an accurate 1/4 mile time comparison, my best has been a 15.5@90mph, and with this diff was 15.5@88mph - the reason the times are so poor is because my computer is pouring in fuel like you wouldnt believe, so it pretty much wont rev past 4500 in any gear other than 1st.

my last run with the 3.9s it was in 4th gear at 4500 about 80m before the finish line, not accelerating at all and missfiring (stupid piece of S()&#$^@#*!!!!)

so the potential is there for a good time, but the comp is holding the car back.

the best thing to do is get hold of a skyline LSD of whatever ratio you want, take it to a diff shop (if you are handy with tools and can do without your car for a while take your diff out and give it to them too) then they will only charge you labour for replacing bearings/seals/oil and 'lapping' in the diff gears, and you pick it up take it home and put it in yourself.

as pretty much a rule you wont be able to find a diff shop that will replace just gears - they all insist on doing bearings and seals at the same time.

i would go 3.7LSD for a compromise, but 3.9s are sweeeeet :D
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