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1987-1993 Mustang FAQ


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I wrote the following FAQ for another site last year. Hopefully the members here will find it useful.


Q: What is the largest size tire you can run on an 87-93 Mustang?

A: '87-'90 Mustangs have a smaller inner fenderwell, which slightly hinders running a monster tire. '91-'93 have a slightly larger inner fenderwell, which will permit for a bit more meat. For example, I run a 275/40/17 on the rear of a '89 LX. To do this, the quad shocks had to be reversed, and the inner fenderwell finnessed with a mallet (don't get scared, it's nothing visable). On the flip side, a friend is running a 315/35/17 on his '93 LX. He also had to flip the quad shocks and beat his inners a little bit. To the best of my knowledge, the largest tire that can be run on a 1987-1990 is a 245/45/17. You have a little more room to play with on the 1991-1993.


Q: What rear gears does my Mustang have?

A: *If* your Mustang is in stock form, and your door tag is intact, you can find out by following this simple formula ~~~> http://www.badassmustangs.com/tech/idx/9/014/article/. If you're unsure, or your door tag is missing, you can do this. Jack the rear of your Mustang up. Mark your driveshaft with chalk or paint. Have a friend slowly turn the tire of your Mustang. Count how many times your chalk mark turns during one full tire rotation. Example: Your chalk mark rotates nearly 3 and 3/4 full turns........this would be 3.73:1 rear gears.


Q: I have a Mustang GT, but I really like LX taillights. Can I swap JUST the lenses?

A: Because the taillight housings are the same, you can swap out just the lenses. You can use a razor blade to carefully separate the seal from lense to housing. You can reapply a new seal with an adhesive agent made just for lights, windows, etc. This is available from any auto parts store.


Q: What areas are prone to rust on a Fox body Mustang?

A: The areas in which a Fox body is prone to rust are as follows: Fenderwells, hatch/trunk, around the sunroof, around the 1/4 windows. If you notice any rust in these areas, you'll want to get it checked out, as it likes to spread quickly.


Q: What are the advantages of removing the front sway bar?

A: Removing the front sway bar on your Mustang allows for better weight transfer for drag racing. However, bear in mind that when you do this, your Mustang will suddenly take corners like a Lincoln Town Car would. Excellent thing to try for the track, but probably not a good idea to daily drive without the sway bar.


Q: What are the pros/cons of running a drag radial on the street?

A: Myself, I can't think of any Pros. The tires wear quickly because they are composed of soft compound. If you get caught in rain (not even a storm.......think more of a spring shower) the car has ZERO traction......ask me how I know. For some, it's not feasible to change the tires constantly. So, if you must run them all the time, beware of rain, and check for wear regularly.


Q: Are there any "weak points" in the '87-'93 Mustang?

A: As with any car, there are a few things that are prone to breakage. The most common (although trivial) is the console ashtray door. In the case that your door fails, there is a repair kit made by Mavromont Industries. Brakes are a definite low point. They'll suffice, but could have been much better. As with any Mustang from '84-'95, the tranny is VERY weak. In a daily driver, it isn't much of an issue, but in a car you beat the crap out of, it can become a problem. Perhaps the BIGGEST problem Fox Mustangs have is a weakness in the Torque Boxes. This is the area where your lower control arm bolts to your chassis. I've seen guys rip their torque boxes just launching on drag radials. You want to check this area regularly, and definitely reinforce it if you beat the tar out of your Stang.


Q: Can you pass emissions with an off-road h-pipe?

A: To my knowledge, no (at least in my area). When your car lacks converters, the h-pipe is "straight-through"........which means there's nothing there to filter out those gases. Furthermore, any car with an off-road h is going to fail a visual inspection, right off the bat.


Q: My car is all stock, and I just found a deal on 36# injectors and a 75mm mass air sensor to match. How much HP will I gain?

A: Bigger isn't always better. When deciding on your combination, it's important to make sure everything MATCHES! 19# injectors can support even a high 12 second car (been there, done that). With those 36# injectors, you're getting way too much fuel. Build up your motor a little first, with the basic bolt ons, then move on to things like injectors, mass air meters and fuel pumps *as needed*.


Q: What are the "basic bolt ons"?

A: The basic bolt ons are known as underdrive pulleys, cat back exhaust systems, cold air induction, throttle body, gears. Intermediate mods would be mass air meter, injectors, fuel pump, cylinder heads, camshaft, intake. Extensive mods would be a stroker motor, supercharger, turbocharger, or nitrous oxide. The last group requires a car that has an adequate fuel system, and mods from the other two groups that would support the combo.


Q: What size valves are in E7 heads?

A: 1.78 intake, 1.46 exhaust. GT40P heads have 1.84 intake valves, and a stock E7 size exhaust valve. GT40 irons (93-95 Cobra and Lightning) feature a 1.84 intake, 1.54 exhaust.


Q: What size injectors are stock?

A: 19# (orange top) injectors are stock size in a GT/LX 5.0. 24# (blue top) injectors were stock in a '93 Cobra.


Q: What size fuel pump comes in a Fox body from the factory?

A: 87-93 Mustangs came from the factory with an 88 lph fuel pump. 1993 Cobras had a larger one, 110 lph I believe.


Q: What differs on a 94-95 5.0L?

A: Lots! The front drive system is different. Different timing chain cover, water pump, alternator + bracket, power steering pump + bracket. The headers are different in that the have an EGR "bung". The upper/lower intakes are different (they have a built-in elbow, and do NOT use the spacer), The pistons are hypereutectic (93-95), and they utilize an electric fan, rather than a clutch fan. Certain components are interchangeable (such as cylinder heads, camshafts). The 87-95s all have the same compression ratio, which is 9.0:1.


Q: Can I use a 94-95 T5 in my 87-93?

A: Yes, you can. However, you must use the matching 94-95 bellhousing and clutch fork. I've seen people misinform others that they must have their driveshaft modified to do this. Untrue. I ran this exact set up in a 1991 LX, using the above parts, and it all worked just fine. Save yourself the money and the hassle. On a side note, the Fox T5 will also fit in the 94-95.......just reverse the process, and use the 87-93 bellhousing and clutch fork.


Q: Which year Mustangs cam equipped with Mass Air?

A: Mass air was introduced in 1988 on California-destined Mustangs. It became the standard in 1989.


Q: How much transmission fluid does my T5 hold, and what type?

A: It'll hold close to 3 quarts (around 2 and 3/4 quarts). Be sure to use a non-synthetic ATF (automatic transmission fluid). Do *not* use "type F"!

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