Read this over and see what you think. I would get a K&N air filter at the same time that way nothing will get through crappy paper filter!
One FREE thing you can do to your Mustang to gain some "pep" is to remove the air intake silencer. *This is located on the passenger*side of the engine compartment. It is a rubber molded piece that extends off the plastic air filter housing. It extends into the fender well about 7" or so.
1.) First un-latch the air filter assembly, 2 latches on the 3.8L V6, one large "top" latch on the 4.6L SOHC.
2.) Unscrew the bolt that holds the air filter in place. There is only one bolt. It can be seen in the above photo. Use a socket set & wrench.
3.) Lift out the entire plastic air filter assembly. The assembly is held in place at the bottom with 2 large rubber grommets. On the 3.8L there is a plastic tab at the bottom of the assembly that holds it to the MAS Air assembly, lift up and out, not forward. On the 4.6L SOHC the metal latch is attached to and comes out with the air filter assembly. Lifting it straight up was easiest for me. The rubber intake hose can bend slightly to accommodate this procedure. Make sure you don't cut or pull loose any MAS Air sensor wires when doing this.
4.) Separate the "rubber" intake silencer from the "plastic" air filter housing. Just pull it loose.
By removing the air silencer you more than double the size of the outer intake port on your Mustang. With this thing in place, it's like trying to breathe with puckered lips.
5.) Re-assemble the air filter cover. Re-secure the air filter to the MAS air assembly, insure a proper seal, don't force anything . Drop the air filter housing back down, securing the two large rubber grommets at the bottom of the air filter housing. Re- latch the air filter housing to the MAS air assembly. Re-bolt it back in place (single bolt at the top) .
6.) Wash your hands, then drive ! Oh.. keep the air silencer handy. In the future you may put it back as part of a "ram air" system or whatever.
After your finished, you will be able to see the conical shaped air filter element slightly (if you lean over and look). For the most part, the air filter is still enclosed but with a much larger opening.
DOES IT REALLY WORK ?
I drove my Mustang 4.6L SOHC V8 with the air silencer in place for the first 5000 miles. After removing it I did feel a difference in power. The engine revs quicker and feels like it has more "pep". *The car sounds a "tiny" bit louder at lower RPM, a growl type sound. *I don't remember feeling this much of a power improvement when removing the air silencer from the '89 5.0 GT. I can't really say I "feel" a difference on the 3.8L engine either. I do feel a noticeable difference on the 4.6L SOHC.... Like getting a power chip or something.
*Drive your car just before you remove the air silencer, then drive it again right after removing it. This way you may be able to notice the difference.
