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.

A chart containing transmission gear ratios for the Fox Body Mustang

1st Gear 2nd Gear 3rd Gear 4th Gear 5th Gear
83-84 T5 2.95 1.94 1.34 1.00 0.72
85-93 WC T5 3.35 1.93 1.29 1.00 0.68
Z-spec T5 2.95 1.93 1.29 1.00 0.63
AOD 2.84 1.55 1.00 0.67 NA

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.

simulation of stock 5.0 dyno

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.

Gear 2.73 3.08 3.27 3.55 3.73 3.90 4.10 4.30
83-84 T5 0.72 1539 1737 1844 2002 2103 2199 2312 2425
WC T5 – 5th gear 0.68 1454 1640 1742 1891 1987 2077 2184 2290
Z-spec T5 – 5th gear 0.63 1347 1520 1614 1752 1840 1924 2023 2122
AOD – 4th gear 0.67 1433 1616 1716 1863 1957 2047 2151 2256

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

Gear 2.73 3.08 3.27 3.55 3.73 3.90 4.10 4.30
83-84 T5 – 5th gear 0.72 2053 2316 2459 2669 2805 2932 3083 3233
WC T5 – 5th gear 0.68 1939 2187 2322 2521 2649 2769 2911 3054
Z-spec T5 – 5th gear 0.63 1796 2026 2151 2336 2454 2566 2697 2829
AOD – 4th gear 0.67 1910 2155 2288 2484 2610 2729 2869 3009

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.

MPH 60 65 70 75 80 85 90 100
83-84 T5 – 5th gear 2002 2169 2336 2502 2669 2836 3003 3337
WC T5 – 5th gear 1891 2048 2206 2363 2521 2678 2836 3151
Z-spec T5 – 5th gear 1752 1898 2044 2190 2336 2482 2627 2919
AOD – 4th gear 1863 2018 2173 2329 2484 2639 2794 3105

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.

MPH 60 65 70 75 80 85 90 100
83-84 T5 – 5th gear 2103 2279 2454 2629 2805 2980 3155 3506
WC T5 – 5th gear 1987 2152 2318 2483 2649 2814 2980 3311
Z-spec T5 – 5th gear 1840 1994 2147 2301 2454 2607 2761 3067
AOD – 4th gear 1957 2120 2284 2447 2610 2773 2936 3262

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.

MPH 60 65 70 75 80 85 90 100
83-84 T5 – 5th gear 2312 2505 2697 2890 3083 3275 3468 3853
WC T5 – 5th gear 2184 2366 2548 2730 2911 3093 3275 3639
Z-spec T5 – 5th gear 2023 2192 2360 2529 2697 2866 3035 3372
AOD – 4th gear 2151 2331 2510 2689 2869 3048 3227 3586

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.