88_5.0

any serious mod will require mass air, cams, possibly full exhaust.

roundman

get some 1-5/8" equal length shorty headers to go with that off road H-pipe, a 2.5" cat back exhaust with free flowing mufflers, some gears like 3.73's or 4.10s, some good tires or preferably slicks and put the car on a severe diet to lose some dead weight out of it. add a chip to the ECU and bump the timing up some and use the highest octane gas available in your area. this will keep the sleeper look and get you close if not into the 13's if you can lose the weight.

JDP

well i have an 86 gt but im pretty sure its not an 86 motor, because it was replaced with a newer motor recently. i have no a/c on the car, and i ran it with full interior (no weight reduction) but just a full exhaust and a gear helped me to break 13s on street tires. So if you got a gear, full exhaust and planted the power with some good tires, you shoud be able to get 13s