What is the Right Gear for my Fox Body Mustang?

Factory V8 Fox Body Mustangs (those that came with the 8.8 rear-end starting from 1986) came with 2.73 gear ratio for 5-speed manuals and 3.08 or 3.27 for the automatics. Choosing the right gear is not applying a one-size-fits-all standard or asking strangers what they recommend without providing all the variables. It really depends on what you want the car to do and how everything aligns with your engine/transmission setup.

Starting with the details

To calculate the right gear scenarios, in the simplest terms, you need to know what your tire diameter is, what the final gear ratio is, what speeds you are trying to reach and what your powerband is. For example, if you want to be at 6500RPM at 130MPH in 4th gear (T5) with a 26″ tire, you may want to look at a 3.90 gear set for your 8.8.

• The stock tire diameter is 25.74″ (based off 225/55R16, here’s a calculator)
• RPM Formula: (((Rear Gear x Trans Gear ) x MPH) / Tire) x 336 = RPM

A chart containing transmission gear ratios for the Fox Body Mustang

What is powerband?

Simply put, a powerband is the RPM range around peak power output. A lot of modifications (specifically heads/cam/intake) will increase your engine’s max output but at the cost of the lower-end power. Below is a sample dyno graph of a typical stock 5.0, you wouldn’t want to change your gear ratio that will force you to shift past 6000RPM in this case.

RPM chart @ 60MPH with different gears

The chart below will help you estimate your RPM at cruising speed (60MPH), numbers are calculated with a 25.74″ tire diameter.

Same chart but at 80MPH (who cruises at 60?)

Below is an interesting chart of a Fox Body Mustang equipped with a Z-spec T5, 4.10 gears, and 25.74″ tire size, shifting at 6200RPM. Here’s the website that allows you to play around with the data, pretty cool! Keep in mind this is all theoretical, I doubt the fox in question can do 184MPH!

What others are recommending

In general, people often suggest going with 4.10’s if you have an auto fox to really “wake it up”. And 3.55/3.73 for T5 equipped fox body Mustangs. However, these suggestions may not work for what you want to do and how your drivetrain is setup. But we will try and break it down below.

3.55 Gear ratio

The 3.55 is a popular choice among those with T5 Fox Body Mustangs, offers a better daily-driver experience but won’t be much of a performance jump for the cost of gears & installation. It will bring you to approximately 1900RPM at 60PMH with a WC T5. If you have an AOD auto, the 3.55 gear ratio will NOT be a wise investment as it won’t offer much improvement over the stock gear, especially if you have 3.27’s.

3.73 Gear ratio

This is arguably the best “all-around” gear for the fox body Mustang, it won’t destroy your MPG and your cruising RPM @ 60MPH is just under 2000 and potentially out of “drone noise city”. It’s also a good middle-ground gear ratio that will work with a lot of possible future drivetrain modifications. It’s also a good choice for the AOD cars.

4.10 Gear ratio

“Don’t fear the gear” they will tell you. If you have an AOD Fox Body, 4.10’s are worth every penny. The AOD’s first gear is numerically low and the overdrive gear is steeper than the T5. If you’re interested in increasing your Automatic Fox Body’s performance, the 4.10 is a great choice, your estimated cruising RPM @ 60MPH will be just over 2000. If you have a T5 behind a stock 5.0HO, it’s not really recommended as these stock engines run out of breath real quick. If you have an HCI setup that changes the powerband and you need to shift it much higher than stock, 4.10’s (or more) may be your ticket. The Z-spec T5 also offers a numerically lower 1st gear and 4.10’s on that transmission is somewhat comparable to having 3.73’s on a regular W/C T5.

In conclusion

If you look at individual modifications and not “the big picture”, you are in for a world of hurt and possible mismatched performance parts that may make your fox body slower than stock. Even with gears, you need to think about what you want to get out of your fox and how the gear will bring the power to the ground by matching it with your engine’s powerband. If you have lots of low-end grunt (like stock), you may not want a 4.10 gear, if your 5.0 is modified to the point where its a dog below 3500 RPM, a stock 2.73 will make your life miserable.