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Discussion Starter #1
3.7, 3.9 and 4.3 right?

What is the overall best ratio IYO?
 

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LSD

Umm , I think that my car has around a 3.42 or something..??

And believe i would be better off with a 3.7 or something, maybe a 3.9......
 

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///M3 > MKIII
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Im running a 4.30 ratio......I like it, car revs faster, gave me a couple tenths in the quarter, have not noticed too much change in gas mileage.....man watch out when its wet out though!! YOu'll spin tires like crazy. 1st , 2nd and 3rd.
 

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dam dood, 4.30 I had those in my MKII.. Doesnt that get annoying on the highway, I like to cruise 80MPH at 3K RPM not 4500.. LOL
 

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testing (figuring)

Is it true that you can put it in the 1:1 gear (4th) and go seventy miles an hour, and your RPMS tell you the gear ratio?

ex: 70MPH in 4th gear = 3,420 RPM, Than is ur gear ratio 3.42?
 

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gear

Remember, fouth gear not fifth, give it a try and let me know..

And some other people, tell me what you get.... To be honest I dont see why it would NOT work, if you are in a 1:1 ratio, at a fixed speed, why couldn't it be true...

Also, my tires are a LITTLE oversized, would that make a difference?
 

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when im dippin at 70 on the highway my tach is pinned exactly at 3g's...hmmm anybody know the stock gear ration for an NA auto? just curious when i hit 80, im doing about 3500 i think too, so its not that bad
 
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Discussion Starter #10
James0598, you have to take the tire diameter into consideration. You are correct that if I do 4300RPM in 4th at 70, then by changing to a 3.9 diff I should lower my RPM to 3900 and go the same speed. A good rule of thumb, however, you can't work it the other way.

If I have 18 inch wheels, and you have 16, I am going to go 56.52 inches (discounting tires) and you 50.24 inches per wheel revolution. What about different size wheels offered by the maker on the same car? Tire aspect ratios?

The standard differential ratios, which can be found on the door jam or engine bay sticker(1986-88) follow are below. All are 4-pinion 8" differentials:

w/o sport pkg :G284 4.300 open
w/ sport pkg :G285 4.300 LSD
turbo (87-88) :G305 3.909 LSD
turbo (89-92) :G315 3.727 LSD

There was also a 4.100, labeled a G295, which was not offered in North America as far as I know.

FYI, My 86.5 NA does just about 70 at 3500 MPH in 5th. This gives it a theoretical top end 130MPH at 6500; but the car can't pull 6500 in 5th gear.:(
 

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i have a G282 diff. on my 89 N/A. But ive never heard of anyone having this one. I checked my tag on my door jam, and thats what it tells me.

it says a g282 has only 2 pinions, is this a set back?
 
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Sounds like a weight-reduction effort:D

Do you know what your ratio is. If G=8 inches, then you should have a 4.300 with 2 pinions. Was this built for the US or Canada?
 

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just wondering if any one knows whats is required to switch from an open rear diff to a 4.3 LSD on the NA. do u have to have a differen drive shaft or axles or anything?

i have a 86.5 and the rear diff is going, its starting to click on take off and rolling. figure i might as well upgrade
 
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