3:73 or 3:90??? - Ford Mustang Forum
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post #1 of 15 (permalink) Old 03-14-2018 Thread Starter
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3:73 or 3:90???

Trying to decide which gear to run.Lots of choices in manufacturers for the 3:73,not many for the 3:90,and most complain of whining with the 3:90.What are others on here running?

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post #2 of 15 (permalink) Old 03-14-2018
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3.73s are a good balance, but if you're thinking about going for 3.90s, you might as well go for 4.10s

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post #3 of 15 (permalink) Old 03-14-2018
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If you are running on the street I wouldn't go higher than 3.73's.
Also if you have an auto you can get away with the 3.90's . In my opinion
3.55's are an all around gear for the street with a 5 speed.
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post #4 of 15 (permalink) Old 03-14-2018
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3.55's are perfect for a street car with a 5speed and you dont lose any top speed.3.73's are usually better if you're spending more time at the track vs the street.1st gear is practically useless with a 5speed and 3.73's on the street.A bigger rear tire will reduce this a tiny amount, but not much.3.73 - 3.90 - 4.10 will work better in an automatic.Any gear set will whine if the backlash isnt set correctly or other things arent installed correctly.

1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
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post #5 of 15 (permalink) Old 03-14-2018
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Originally Posted by thunder1335 View Post
3.73s are a good balance, but if you're thinking about going for 3.90s, you might as well go for 4.10s
I have 4.10's with an AOD. In overdrive at 80 mph, I'm going about 2700rpm's. STAY AWAY from Richmond gears, they are very noisy. Google "Are Richmond gears noisy"?, and look at the responses. Below is just one quote I copied you.

My only experience with noisy gears has been with the Richmond Pro gears. They are cut differently than Ford gears and the Pro gears are made from a different alloy.

In my 'crew' -- several of us do rear ends and the others using Richmond Pro gears noticed whining right away.

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89 LX Notch: Floo-Tek 5.0X heads, GT-40 intake, B-303 cam, Dynamic 3800 converter, 4.10:1 gears & lots of suspension work. 12.50 @ 106.42 MPH.
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post #6 of 15 (permalink) Old 03-14-2018 Thread Starter
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Thanks for the info.Most of what I’ve read on the AM and LMR sites from buyers is the same,all suggesting going with Ford gear sets.Based on that there is no 3.90 sets available from Ford that I have seen,so I guess my only choice is 3.73 or 3.55.I’m running a 5spd too,i noticed I didn’t mention that in my post.
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post #7 of 15 (permalink) Old 03-14-2018
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Originally Posted by Robs87GT5.0 View Post
Thanks for the info.Most of what Iíve read on the AM and LMR sites from buyers is the same,all suggesting going with Ford gear sets.Based on that there is no 3.90 sets available from Ford that I have seen,so I guess my only choice is 3.73 or 3.55.Iím running a 5spd too,i noticed I didnít mention that in my post.
If those are the only choices, i would recommend the 3.73's. Good luck.

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89 LX Notch: Floo-Tek 5.0X heads, GT-40 intake, B-303 cam, Dynamic 3800 converter, 4.10:1 gears & lots of suspension work. 12.50 @ 106.42 MPH.
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post #8 of 15 (permalink) Old 03-14-2018
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Quote:
Originally Posted by Howelldaddy View Post
I have 4.10's with an AOD. In overdrive at 80 mph, I'm going about 2700rpm's. STAY AWAY from Richmond gears, they are very noisy. Google "Are Richmond gears noisy"?, and look at the responses. Below is just one quote I copied you.

My only experience with noisy gears has been with the Richmond Pro gears. They are cut differently than Ford gears and the Pro gears are made from a different alloy.

In my 'crew' -- several of us do rear ends and the others using Richmond Pro gears noticed whining right away.

In my opinion,its best to just stick with Ford Racing gears.
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1991 Mustang lx
D.S.S. 342ci {10.5:1}
TFS 190cc + track heat
Lunati 61011 .549".565"
Pro-M 76mm maf
Jetronic 30lb inj
QA1 Coilovers
17" Weld ProStar XP's
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post #9 of 15 (permalink) Old 03-15-2018
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Quote:
Originally Posted by Robs87GT5.0 View Post
Thanks for the info.Most of what Iíve read on the AM and LMR sites from buyers is the same,all suggesting going with Ford gear sets.Based on that there is no 3.90 sets available from Ford that I have seen,so I guess my only choice is 3.73 or 3.55.Iím running a 5spd too,i noticed I didnít mention that in my post.

Pretty hard to beat Ford gear sets IMO. I run both the 3:55 and the 3:73's in my two coupes. The 92 has the 3:73 Ford Racing gear set; the 89 has the 3:55 Ford motorsport gear set (scrap yard). Both are backed by the 5 speed. The 89 Motorsport 3:55 gear set came out of the F150. If you go the Motorsport gear set, you will notice a small ridge on the ring gear itself compared to the Ford Racing gear set.; (the ridge is inside the ring gear almost to the back side). It has no effect on installation or on the performance part though.

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Avoid Richmond, go with Ford's set? I feel like the odd one out for having bought a set of 4.10s from Assault Racing off eBay...
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What is the motor setup? Stock heads and such?
I went from 2.73 to 3.73, and now I'm in the process of having the 3.73's swapped for a 3.31. When I went from the 2.73 to the 3.73 it was still slow, I was just shifting sooner.
The 3.73's were pretty much a pain. Maybe if I went with 3.55 originally I'd have stuck with them. I bet I put less than 10k miles on the 3.73's. I just got tired of being revved up all the time.
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post #12 of 15 (permalink) Old 03-16-2018 Thread Starter
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Someone mentioned that with 3.73 1st gear is basically useless.Do I assume 2nd gear starts work well?
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post #13 of 15 (permalink) Old 03-16-2018 Thread Starter
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Quote:
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What is the motor setup? Stock heads and such?
I went from 2.73 to 3.73, and now I'm in the process of having the 3.73's swapped for a 3.31. When I went from the 2.73 to the 3.73 it was still slow, I was just shifting sooner.
The 3.73's were pretty much a pain. Maybe if I went with 3.55 originally I'd have stuck with them. I bet I put less than 10k miles on the 3.73's. I just got tired of being revved up all the time.
I’ve currently got 2.73’s but won’t have the car on the road until I’m done with the motor.As for the motor:
-ported/polished gt40p heads
-TMOSS ported gt40 Intake
-75mm TB
76mm MAF
24lb injectors
Fuel pressure regulator/255lph pump
B cam 1.7rr advanced 2*
Electric fan,no smog
Shortys,x pipe
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Quote:
Originally Posted by Robs87GT5.0 View Post
Quote:
Originally Posted by 90lxwhite View Post
What is the motor setup? Stock heads and such?
I went from 2.73 to 3.73, and now I'm in the process of having the 3.73's swapped for a 3.31. When I went from the 2.73 to the 3.73 it was still slow, I was just shifting sooner.
The 3.73's were pretty much a pain. Maybe if I went with 3.55 originally I'd have stuck with them. I bet I put less than 10k miles on the 3.73's. I just got tired of being revved up all the time.
I’ve currently got 2.73’s but won’t have the car on the road until I’m done with the motor.As for the motor:
-ported/polished gt40p heads
-TMOSS ported gt40 Intake
-75mm TB
76mm MAF
24lb injectors
Fuel pressure regulator/255lph pump
B cam 1.7rr advanced 2*
Electric fan,no smog
Shortys,x pipe
I think I'd prob go w 3.55. You'll probably "make power" up to 6k I bet.
Really there's not that much difference between 3.55, 3:73, and 4.10 how fast it'd accelerate. You're talking about fraction of a second slower or faster. With 3.73s it took me three shifts to reach 60 mph w a 6k rpm redline.
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I will agree with 90lxwhite as well since this is more of a street car 3.55 will be more forgiving all around.


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