I have a 1986gt cov ,with 70k on the motor it runs stong ,so do I think .cold air and xpipe and no cats are the only mods.what and why should i do to the motor to make it faster. thanks
'86s are finicky beasts, because the cylinder head/piston combination is different from any other 5.0 Mustang. No aftermarket head will fit on an '86 aside from TrickFlow Twisted Wedge heads, because the '86 has true flat top pistons with NO valve reliefs. TFS heads have a unique valve arrangement that supposedly doesn't require valve notches for clearance. The stock heads on the '86 are "E6" castings, which have a "fast burn" chamber that shrouds the intake valve. These heads are NOT good for performance use; even with porting they still suck.
So your options are to either run TFS heads with a mild cam on the stock short block, or build a new shortblock with pistons that have valve reliefs.
FYI, I have an '86, and my plan is to run TFS heads on it starting this winter. My car has been to the track, and just for an example of what you can expect from a '86 with stock heads, this is my setup:
GT40 intake (Explorer) with MILD porting
70mm TB
CAI
3.73 gears
Headers and full exhaust
E-fan
Short belt (no smog or A/C)
Mild suspension setup
Stock heads and cam
I hot lapped the car on street tires and ran low 14s in the quarter. Can't remember what my 60s were, but they weren't particularly good. I think on drag radials and a cold engine it is a high 13 car. A similar setup on an 87-93 car would be good for mid/low 13s for an average driver or high/mid 12s with a good driver, so you can see how much the E6 heads hurt performance.