Drivetrain Rear axle gears

Exrace89GT

Member
Mar 29, 2019
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What rear gear ratio. A little history. 89 GT, 306, stock cam, Explorer heads and manifold with egr and the air injection. Have to pass California smog check. T5 out of a 92 5.0. I want to go to 3:55 or 3:73. So which one is best for the street.
 
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B.D. Magoo

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Jun 17, 2020
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I had the 5.0 out of a 98 exploder with a E cam in my 85/88 frankinmutt, stock gt40p engine except cam. I have a 8.8 rear end from a 93GT with 373 gear and a locker, went from 308 to the 373. Honestly when I 1st changed it I didn't like it, made drivability difficult for the drop in fuel mileage, top speed went waaay down, and 1st gear was almost useless, I would rather had the 355 gears instead to find a better medium. Now I have a little more engine and the 373 gears are great. My advice, look at your end plans not current situation and build accordingly. It might be a little much now but just what you want or need later.
 

2000xp8

SN Certified Technician
Aug 8, 2003
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top speed went waaay down
3.73's should be good for somewhere in the range of 160mph with a t5 transmission.
Down from somewhere around 190mph with 3.08's.
So while technically you could be right, your top speed is indeed down, i'm not so sure about how relevant those numbers are...
And typically the more "engine" you have, the less gear you need.

Exrace, either ratio is fine, the 3.73's are a bit more aggressive, but consider most people would not waste their time changing between the two.
So the reality is, you could go either way and be fine.
With that said, you will likely find the seasoned guys here suggest 3.55's.
 

KRUISR

Well-Known Member
Apr 16, 2015
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The key question is what you want the car to do. If you are looking to cruise around, behave with speed limits and hit the occasional 100-110mph, I would go with the 3.55s. As stated above, higher numbers will virtually eliminate first gear or make you really good at 1st/2nd powershifts.

If you want to race top speed with vipers, vettes, ... you will need more power and something even lower (3.08/3.27). But if I remember right when they were new the published top speed of the Foxbody was 145 or 149. At that point you have aerodynamic drag to deal with if you want to go faster (not just gear ratio and RPM math as used above).
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Something rarely mentioned when talking rear gear ratio is tire height, a 373 with a stock height tire makes first gear pretty much useless for regular cruising, a 355 gear is a happy medium for stock or mildly modified street car.
 
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Willybill32

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Jul 16, 2019
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The key question is what you want the car to do. If you are looking to cruise around, behave with speed limits and hit the occasional 100-110mph, I would go with the 3.55s. As stated above, higher numbers will virtually eliminate first gear or make you really good at 1st/2nd powershifts.

If you want to race top speed with vipers, vettes, ... you will need more power and something even lower (3.08/3.27). But if I remember right when they were new the published top speed of the Foxbody was 145 or 149. At that point you have aerodynamic drag to deal with if you want to go faster (not just gear ratio and RPM math as used above).

I replaced my stock 2.73 with 3.55 gearing. I don’t plan on racing or track time, but wanted a compromise between comfortable cruising and performance. No complaints so far.
 
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