No its not possible to get optimal exhaust flow with only one pipe. I have an 83' and I've tried all kinds of configurations with the exhaust. What works best for me are a set of BBK headers, each with their own 3" pipe and Magnaflow muffler. I didn't connect another pipe to the end of the mufflers, instead I put on downward aiming tips which dump the exhaust out and downward before the differential. Otherwise, you would have to bend piping up and over your differential and out of your back bumper, which ultimately creates power-loss from extra pipe weight, and complicated bends for the exhaust to pump through.
if you don't want to go all out and convert to dual exhaust, a single 3" pipe actually flows more than dual 2.5" pipes and should also give better low-end torque. the problem is that its almost inpossible to get anything larger than 2.5" to go over the rear axel, so a single pipe would pretty much have to use exhaust dumps like Dakine858 described. if your state is like mine where the exhaust pipes must extend to the perimiter of the vehicle, you'd be best to go with a dual 2.5" setup
Seems that I remember when converting factory single exhaust cars to duals, you must change out the trans mount crossmember. The original one only has a "hump" on one side. Not a big job, just a bolt in, but it needs to be done.
Yes, you'll need a double hump crossmember. But is the engine stock? If it is, you wouldn't gain like you might think you would, because the 1983 wasn't huge on power and a larger (or dual) exhaust could cause it to lose some bottom end torque. But if you have engine performance mods, you could upgrade to duals. Since you're in the Bay Area, you might want to check to see if such an upgrade would be legal to do before you do it.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, builds, modifications, reviews, engine swaps, classifieds, troubleshooting, maintenance, and more!