Rear axle gear ratios

[70RustBucketList]

Hi all,

Was just wondering if there was a rear differential gear ratio calculator somewhere, or if there was a post with an RPM reference for auto and 5 apeed trans when you swap in different ratios, such as 3.28, 3.55, 3.73, 4.11 and so on. I am exploring the options for the 95 GT, as whatever it has in there definitely feels tall.

Thanks!

 

[94StewFord]

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

 

[GTR]

Hi all,

Was just wondering if there was a rear differential gear ratio calculator somewhere, or if there was a post with an RPM reference for auto and 5 apeed trans when you swap in different ratios, such as 3.28, 3.55, 3.73, 4.11 and so on. I am exploring the options for the 95 GT, as whatever it has in there definitely feels tall.

Thanks!

If you’re lucky the rear end tag is still on the diff cover, it will have the stock gear ratio on it. Old wisdom as I recall call it was 3:73 for the 5 sod. and 4:10 for autos. I put 4:10 in my 5 spd. Way too low. First gear is all but useless. If it’s a daily I’d suggest 3:55. Good all around gear.

 

[joe65]

If you’re lucky the rear end tag is still on the diff cover, it will have the stock gear ratio on it. Old wisdom as I recall call it was 3:73 for the 5 sod. and 4:10 for autos. I put 4:10 in my 5 spd. Way too low. First gear is all but useless. If it’s a daily I’d suggest 3:55. Good all around gear.

Typically fox and sn95s had 3:27s if it was a 5spd. 3:55 was only used in the mach 1s and the cobras. Typically. I'm sure there are, like always, exceptions for special editions etc.

 

[tinnocker]

If you’re lucky the rear end tag is still on the diff cover, it will have the stock gear ratio on it. Old wisdom as I recall call it was 3:73 for the 5 sod. and 4:10 for autos. I put 4:10 in my 5 spd. Way too low. First gear is all but useless. If it’s a daily I’d suggest 3:55. Good all around gear.

I considered the 4.10 but got the 3.73 in my 5 speed. After reading your post, I am glad I did. I love the 3.73 and don't know why Ford didn't have it standard on the GT and Cobra. Oh, I forgot about the milage issues that they would have with the public and the government, but it sure woke up the Mustang.

 

[Daryl]

https://lmr.com/products/Mustang-7-5-8-8-Rear-End-Axle-Info

 

[TrickVert]

Decades of feedback has recommended 3.73's for a "fun-to-drive" normally-aspirated 5-speed, or 3.55's if you anticipate a power adder. If your car is a daily-driver, 3.55's would probably be my go-to, but even 3.31 or 3.27 would be a noticeable improvement over the (likely) 2.73 set that's in there now.

 

[07GtS197]

94-95s generally had 3.08s from the factory.

I had 3.73s in my 02 gt, they were perfect. My 00 gt had 4.56s and I hated them. Way too much gear. Really it felt slower than the 02 but that might just be from the need to shift sooner. Maybe for a higher revving motor they’d be fine but on a bolt on 2v it was too much.

 

[GTR]

When I ordered my 94’ GT the options I was given was 2:?? and 3:08. Asked then for 3:55 and ways flatly denied. Had to do with EPA mileage standards. I may be wrong but I think 3:27 were available in a Cobra.

 

[70RustBucketList]

Thanks everyone for the responses, very helpful. I am trying to calculate what my final drive RPMs would be at, say 80 MPH on the highway, so thansk for linking the spicer calculator, I'm off to play withthat a bit!

 

[96blak54]

Mine came 2.73 and never made it out of 3rd gear during sprint runs. Cruised at something like 1500rpm.

I swapped it in favor for 3.55. I sort of like the 2.73

 

[joe65]

I considered the 4.10 but got the 3.73 in my 5 speed. After reading your post, I am glad I did. I love the 3.73 and don't know why Ford didn't have it standard on the GT and Cobra. Oh, I forgot about the milage issues that they would have with the public and the government, but it sure woke up the Mustang.

yeah the 3;73s in the 2v 5spd make the car worth driving hard. just better response. The 3:55s in my mach 1 really are pretty decent for typical driving. i can floor it in 2nd and break the tires loose. But there's just too much waiting to get to the 6k rpms to shift so in the 4v the 410s really wake the car up.

 

[Monday]

When I ordered my 94’ GT the options I was given was 2:?? and 3:08. Asked then for 3:55 and ways flatly denied. Had to do with EPA mileage standards. I may be wrong but I think 3:27 were available in a Cobra.

You can be grandfathered in for those EPA Standards I assume. You should check again...

 

[Daryl]

Thanks everyone for the responses, very helpful. I am trying to calculate what my final drive RPMs would be at, say 80 MPH on the highway, so thansk for linking the spicer calculator, I'm off to play withthat a bit!

If memory serves, I’m pulling 3500rpm in 5th gear at 80mg running 3.55:1 rear gears

 

[photoracer18]

When I ordered my 94’ GT the options I was given was 2:?? and 3:08. Asked then for 3:55 and ways flatly denied. Had to do with EPA mileage standards. I may be wrong but I think 3:27 were available in a Cobra.

Not in a 94-95 Cobra, manuals were all 3.08. 96-98 were 3.27. What ever you do don't jump 2 ratios. All you get is the same performance in one more gear different. So if 3.08 go either 3.27 or 3.73. I had a Boss 9 with 4.30. It was not good for anything but the drag strip.

 

[Monday]

... I had a Boss 9 with 4.30...

The fella that did the rear end for me told me he ran with 575s. Go to the corner store real quick like. But useless everywhere else 'cept strip

 

[Daryl]

…and yes, I can break mine loose too I nto 2nd gear with my 3.55’s!

 

[Rons95GT]

I bought a new GT in 1990 with a 5- speed. It came from the factory with a 3:08 gear. I lived in FL at the time and spoke to a few performance shops there to get a gear recommendation. It depended on what the plans were for the car but the common advice was 3:55-3:73 for a 5-speed and 3:73-4:10 for an automatic. I have followed that advice and been happy. I went with 3:73 in that 1990 car because it just had all the usual bolt ons and a small NOS kit. I have been running 3:55 in my 1995 GT since 1997 because I knew it was going to have much more power.

 

[Monday]

... the common advice was 3:55-3:73 for a 5-speed and 3:73-4:10 for an automatic...

yep