Top 10 Foxbody Mustang Modifications

Not a true ‘modification’, so to speak, but nonetheless the only place to start on your Fox 5.0 is with a solid tune-up! After all, if she ain’t running well to begin with, she ain’t gonna run well after you mod her, either. In fact, she’ll probably run worse. So, for this reason, modification #1 should be a tune-up to ensure your car is running in top stock form! Check the components below and replace as needed.

- Spark plugs and wires
- Ford Racing 9mm wires (87-93 5.0L, blue)
- NGK V-Power #6945
- Distributor cap & rotor (or distributor itself)
- MSD #8482 cap and rotor (86-95 5.0)
- Accel #8234 cap and rotor
- Ignition Coil
- MSD #8227 TFI coil
- Accel #140012 TFI coil
- Fuel filter
- Motorcraft OEM (83-97)
- Oil filter
- KN #HP-3001 (64-95)
- Motorcraft OEM (87-95)
- MAF sensor
- Timing
- TPS voltage
- Clean stock or high-performance air filter

A super easy procedure which can procure some power gains is installing a high performance air filter (better flow) or simply cleaning out your existing filter.

Furthermore, if you are running a stock air box, if you haven’t already, remove the air silencer. It is a rubber boot piece installed under the stock air filter. Some people claim gains of up to 5HP by just removing the silencer.

A high flow filter may also net a few ponies (2-3HP), but will definitely improve throttle response. All in all, there is a potential for another 7HP by swapping the air filter and removing the stock silencer.

Subframe connectors (hereafter dubbed SFC) are a must for Fox-platform Mustangs (especially convertibles). Their factory unibody structure is inherently weak and even the stock 5.0L at factory rated 225HP and 300 ft-lb power levels can twist and distort the frame and floor pans with ease. SFC’s strengthen the unibody by connecting the front subframes with the rear.

Benefits include a stiffer chassis and better power transfer; power will be better transferred to the wheels instead of some being wasted by flexing the chassis. SFC’s are a must, especially when going above stock power levels. If a stock engine can thrash the frame, imagine what a more powerful motor will do.

SFC’s generally run between $130-$200 a set. Make sure to pick the weld-in, full-length type. Maximum Motorsports full-length subframe connectors for Foxbody Mustangs and are great quality and will really strengthen the frame. Just keep in mind they come unpainted – it’s best to throw on a few coats of black rust paint before installing them.

The second best modification is gearing. Changing the differential gear ratio can transform your car into a whole new animal. Gears will not increase engine horsepower but they will increase vehicle acceleration because of their increased torque multiplication.

Many enthusiasts agree, without a doubt, swapping gears is the best bang-for-buck, seat-of-the-pants mod that can be done on a stock Fox 5.0. The most popular gear choices for street and strip going Stangs are:

Manual transmission: 3.55:1 or 3.73:1

Automatic transmission: 3.73:1 or 4.10:1

Again, gears won’t add power, but they will maximize what power there is. A gear swap will definitely throw you back into the seat. Ford Racing, Richmond (Excel) and Motive are all major players in the gear game.

Foxbodies are known for their terrible, inadequate and underperforming brake system (running drums on a ‘sports’ car?!?!). The best way to improve them is really to go with a rear disc setup, but for simplicity’s sake there are some things that can be done with the stock system to increase performance.

The back end is hopeless, but the front brakes aren’t entirely a lost cause. First off, a good set of pads can go a long way. Hawk Performance pads (HPS series & ceramic street series) are immensely popular for both performance and streetability. Combined with a good set of rotors, both braking performance and brake feel can be greatly increased.

Foxbody Mustangs are also known for their sloppy brake pedal. A great way to manage pedal feel is to swap out the stock rubber brake lines with a braided stainless steel variety. Stainless steel lines won’t expand as much under braking pressure, thus all of your brake fluid force goes to the calipers and not into expanding the lines.

Russell makes a nice kit with the front and rear lines. At the end of the day, a solid front brake setup will cost around $400 for quality pads, rotors, and lines. (~$75 for HPS series, ~$82 for the ceramic series and approx $110 for HP plus).

Changing the extremely restrictive stock exhaust headers to an aftermarket piece (BBK, MAC, etc.) can net ~5HP. (Believe it or not, the stock headers actually were the reason for a ~7HP gain between 1986 and 1987!

Still, they are much too restrictive.) Any aftermarket shorty header is considered a good replacement over the stock manifolds. Aftermarket shorties may net a few HP, but more importantly, have the capacity to flow a larger volume of air for when that 5.0 starts churning out a little more power. Shorties are also very easy to fit and install.

Longtubes are considered to provide more low-end torque than shorties but are more difficult to fit and install. Prices vary depending on the make and finish but figure $250-$350 for a set shorties or $300-$750 for long tubes.

Just like the throttle body, replacing the stock MAF unit (a puny 56mm!) will not give you additional horsepower, but it will lay the foundation to support it later down the road when some more serious modifications are made (heads and intake, here we come!).

When picking a MAF meter keep in mind they must be calibrated with the fuel injectors, so don’t pick a MAF meter set for 24 lb/hr injectors when you’re still running stock 19 lb-ers! Price is dependent on size.

For a stock displacement motor, a 70-80mm unit should do the trick. Figure $150-$250. Companies C&L and BBK are the big dogs when it comes to a new MAF.

The stock 60mm throttle body is a little too small to support a more powerful engine. Stepping up to a 65-75mm (don’t go any bigger than 75mm) can maybe gain 2-3HP, but more importantly, will help support an additional 100-200HP without issue and vastly improve throttle response.

The reason they do this is simple – they simply can flow more air than the stock unit! SR Performance, Accufab, and BBK are the three most popular choices.

OK, here is where we’ll see some promising power gains. The stock intake manifold is very restrictive. Porting the stock lower or swapping to an entirely new aftermarket intake can net some pretty good power.

There are a lot of players out there, but the most commonly used pieces are the Ford Racing Cobra/GT40 intake, Edelbrock Performer/Performer RPM and the Trickflow Streetburner. Holley used to make a really great intake (the Systemax) but it has been discontinued.

Another really popular option is to use a GT40/Explorer intake, which is the same as the Cobra intake (and way cheaper!). Depending on which intake you use (or porting the stock), a minimum 15-20HP gain is totally realistic.

Now we’re getting serious. Barnun, the stock E7 cylinder heads equipped on the 5.0L are a major party pooper. Back in 87′, they freed up some HP, but in the modern day, they are a hopelessly restrictive design.

Porting the stockers (very time consuming, but if you’re on a strict budget, that’s free HP. Don’t pay someone to port them though. Picking up a set of GT40/GT40P or an aluminum aftermarket set can yield anywhere from 30-75HP! (That’s how seriously restrictive the original E7’s are.)

An aftermarket set of aluminum cylinder heads enter the fray priced around $1200. Once all the necessary supporting mods are done, a performance set of cylinder heads will waken up that Fox 5.0 like nothing else.

To complete the top end, a new camshaft may be in order. In all honesty, the stock HO cam is actually a great piece and performs very well for street duty cars. However, if you have swapped out the stock heads and intake, if you really want to maximize power, an aftermarket camshaft can squeeze out an extra 20-30HP if properly matched with the heads and intake and for the intended use of the car.

Comp Cams, Lunati, Crower, etc., are all popular aftermarket camshaft manufacturers with a plethora of offerings. Ford’s own racing division, Ford Racing, has a selection of aftermarket cams too (dubbed the alphabet cams, as they are coded B303, E303, F303, X303). One of the Ford alphabet cams can be a solid choice, however, they were designed a couple of decades ago and subsequently are not as up-to-date as other manufacturer's offerings. Or, if you really want to go all out, consider a custom camshaft.

All in all, a new camshaft will run between $250-$400. It is very important thought that you properly match the camshaft for your vehicle’s application. If you have a street car, don’t pick a cam that starts making power at 3500+ RPM, that won’t be any good! If in doubt, pick up the phone and call any of the cam companies sales/tech reps. Explain to them your vehicle and its purpose, and they should be able to help pick out the right cam.

As a bonus, here is a good mod for T5 equipped Mustangs. For Foxbody Mustangs equipped with a manual T5 transmission, the distance between gears is quite extravagant. It is not uncommon to stretch a tendon when attempting to shift…

A short throw shifter will lessen the distance (hey, that’s why it’s called a ‘short throw shifter’, duh!) between shifts, thus allowing you to bang them out in less time. No horsepower gains here, but they can help run a faster quarter mile. The B&M Pro Ripper, Steeda Tri-Ax, and SR Performance short throw shifters are the most popular and best functioning shifters out there in relation to cost.