Mustangs are a classic platform immensly popular to modify, and for very good reason. The stock 5.0L pushrod, factory rated at 225HP, soon becomes a little under-powered for most enthusiast's tastes. Thankfully, the Mustang aftermaket has absolutely exploded with new or revised designs for just about every aspect of these iconic vehicles. From performance enhancing to restoring, there literally is a part for anyone's desire. The thing is though, you don't want to go about modifying your Mustang by throwing any and every part at it, willy-nilly. No, rather, there is a strategy to picking parts and making power. It's not quite as simple as just dumping in more fuel, unfortunately.
Listed below, for everyone else to read, are the modifications in which I would go about upgrading my Foxbody. Power is fun, there is no doubt about that. However, power cannot be the only focus to create a truely enjoyable vehicle. Below is a compilation of the most common and best-suited primary modifications for any Fox 5.0 based Mustang, 1987-95. A lot of these parts can be purchased used, which can save you a pretty penny. Check Craigslist, various online classifieds or eBay, but keep in mind there is no warranty or guarantee on used parts. If you want to buy the parts new, I personally like dealing with American Muscle.
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.
Subframe connectors (hereafter dubbed SFC) are a must for Fox-platform Mustangs (especially convertibles). Their factory unibody structure is inheritantly weak and even the stock 5.0L at factory rated 225HP and 300 ft-lb power levels can twist and distort the frame and floorpans 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, Steeda, J&M are very popular SFC makers.
The second best modification is gears. 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;
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.
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 simplicities 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) is immensly 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 stainless steel variety. Stainless steel lines won't expand under braking pressure, thus all of your brake fluid force goes to the calipers and not into expanding the lines. At the end of the day, a solid front brake setup will cost around $400 for quality pads, rotors and lines. Near as I can tell, American Muscle currently has the best price (usually free shipping too) on Hawk pads. You can check them out here. (~$65 for HPS series, $70 for ceramic series, $97 for HP plus). You might be surprised at the difference quality pads and rotors can make.
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 make and finish but to throwout a ballpark figure... $250-$300 a set.
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 lbers! Price is dependent on size. For a stock displacement motor, a 70-80mm unit should do the trick. Figure $150-$250.
The stock 60mm throttlebody 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. The reason they do this is simple - they simply can flow more air than the stock unit! (Read here for full specs) Accufab, BBK are popular choices. Throttlebodies generally run around $250. Increased throttle response is not uncommon, either.
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 from Ford Racing (Cobra or Explorer), Edelbrock and Trickflow. 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. For more info, read E7 Ramblings), picking up a set of GT40/GT40P (GT40/GT40P Reference) 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, the most costly single part. 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 manufactuer'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 extravagent. 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 ET. B&M, Steeda, Pro 5.0, Mac, Hurst etc. all make nice kits and generally run around $200. Install can be done at home, no MD required.
All prices listed above are a general approximation of what it would cost to buy the parts new. It is more than possible to find some, if not all, of the above parts used. Check on sites like craigslist and in Mustang classifieds. Just keep in mind used parts don't come with a warranty and you may be buying somebody elses problems. Best do your research, and do it well.