Drivetrain Rear axle gears

Exrace89GT

Member
Mar 29, 2019
76
15
18
79
Lompoc, CA
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.
 
  • Sponsors(?)


B.D. Magoo

Member
Jun 17, 2020
38
1
8
39
Chattanooga TN
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
6,907
1,032
194
NJ
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

Active Member
Apr 16, 2015
260
83
38
50
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).
 
  • Like
Reactions: Willybill32

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
17,327
5,599
193
polk county florida
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.
 
  • Like
Reactions: Willybill32

Willybill32

Active Member
Jul 16, 2019
154
70
38
Lexington, KY
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.
 
  • Like
Reactions: General karthief
Thread starter Similar threads Forum Replies Date
5 Rear end gear noise 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 3
5 3.55 gears for a 87 mustang automatic transmission 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 13
C For Sale Moser 8.8 Rearend Drivetrain Parts 0
A Limited Slip Rear End Grinding and Whining 1996 - 2004 SN95 Mustang -General/Talk- 1
K Rear End/differential SN95 V6 Mustang Tech 6
J Expired Fox Body 1986-1993 8.8" Rear Axle Assembly 3.55 Gears - $190 Drivetrain Parts 1
J Expired Fox Body 1986-1993 8.8" Rear Axle Assembly 3.55 Gears - $190 Drivetrain Parts 0
88-378 Rear Gears, axles, brakes, etc.. Drivetrain Parts 0
chgovfk Rear Axle gear help needed 2005 - 2014 S-197 Mustang -General/Talk- 10
hognutz Rear diff, axles, gears etc SN95 4.6L Mustang Tech 1
H Best Stock Rear Axle/Gears? Swap axle? 1994 - 1995 Specific Tech 4
BugsOli Drivetrain Passenger side rear axle play and clonk Fox 5.0 Mustang Tech 3
D 1967 Ford 8" Axle 1965 - 1973 Classic Mustangs -General/Talk- 3
R Difference Rear axles Mustang II 1974 - 1978 Mustang II Talk & Tech 7
F Drivetrain Rear axle difficult to slide in Fox 5.0 Mustang Tech 4
6 Budget 1969 mustang rear end build 1965 - 1973 Classic Mustangs -General/Talk- 1
A Finally rear axle being attended too 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 37
Mr.T. Suspension Worn out rear axle Anti wrap shock SN95 4.6L Mustang Tech 0
A Rear axle seal removal and installation 1965 - 1973 Classic Mustangs -General/Talk- 2
J Suspension Rear axles Fox 5.0 Mustang Tech 1
C For Sale Moser 8.8 Complete Rear End Drivetrain Parts 0
Willybill32 Need help with choosing a good rear axle ratio 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 35
S Rear Axle and Stock Fan/Shroud help w/ 351w 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 0
G Drivetrain Rear axle play/rattle Fox 5.0 Mustang Tech 3
C 1965 with 8" rear end needs axles - How much $$$$$ The Welcome Wagon 0
ZeroFoxGiven 9in rear end w/disc brakes [Parking Brake] 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 4
N 1966 mustang rear axle 1965 - 1973 Classic Mustangs -General/Talk- 2
B New Car, New Member, rear axle question. The Welcome Wagon 4
Stangel2001 Swap rear axle 1996 - 2004 SN95 Mustang -General/Talk- 0
2fast4u770 Rear axle 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 8
G 2011 Mustang Gt 2010 - 2014 Specific Tech 1
Nightstang00 Axles For Rear Cobra Disk Brakes 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 23
B 90 Lsc Rearend In A 89 Fox Lx 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 6
gruvee87vertgt Rear Axle Seal Part Number? Fox 5.0 Mustang Tech 3
G SOLD 1992 Mustang Rear Axle-complete 5 Lug Drivetrain Parts 0
Josecomputertech 2011 5.0 Stick Shift Rearend 2005 - 2014 S-197 Mustang -General/Talk- 3
86mustanglx Brakes Sn95 Axles In Fox Rear Fox 5.0 Mustang Tech 4
M 1967 Mustang Rear End 1965 - 1973 Classic Mustangs -General/Talk- 3
M 1967 Rear End Classic Mustang Specific Tech 2
NVERL8 Rear Brake Trouble Or Axle Bearing Or ? Classic Mustang Specific Tech 8
M 2002 Mustang Rear Diff Side To Side Slack 1996 - 2004 SN95 Mustang -General/Talk- 1
Jordan Warta Can't Fit Aftermarket Exhaust Tailpipe Over Rear Axle? Fox 5.0 Mustang Tech 3
9 Rear Axle Going Bad? 1996 - 2004 SN95 Mustang -General/Talk- 0
N 88 Lx Rear Axle Damper Rubs New Tire Fox 5.0 Mustang Tech 12
Edbert Rear Axle Brake Lines 1965 - 1973 Classic Mustangs -General/Talk- 0
Ian Ranchero 1967 Rancgero 9" Rear Axle Stuck 1965 - 1973 Classic Mustangs -General/Talk- 2
modulistic 4.6 Swap Underway. Need Ideas To Solve Rear Axle Problem. Fox 5.0 Mustang Tech 31
J Rear Axle 1994 - 1995 Specific Tech 1
J '06 Gt Auto, Rear Axle Noise Help 2005 - 2009 Specific Tech 1
D Progress Thread 1965, 8" Locker Rear Axle Questions 1965 - 1973 Classic Mustangs -General/Talk- 2
Similar threads