I need help chooseing the right size pipe to run with my setup for the best gains (see sig) I'm gonna run true duals. what you guys think?

2.5'' would be the max I would go, what kind of heads do you have?

The heads are just stock heads that I ported and polished ...I didnt modify the chambers just the intake and exhaust runners ..to give you an idea of how much material was taken away, if I take out a valve cover bolt I get a vacume leak on the intake side . on the exhaust side I didnt go as far but I still took a great deal away and polished the exhaust to a glass smooth finish ..Oh and I'll be useing hedman shortie hedders

2.5" duals. 3 or 3.5" single.

I think im gonna go with 2.5" duals ...thanks for help guys !!!:hail: :hail:

i have the same question about my car, i'm getting a new flowmaster muffler and i wanna know if i should i get the muffler with dual 2.5" outs or dual 3" outs? my car is an 89 rs 305 tbi all stock.

viper, the inlet diameter is what is important as long as the outlet is as large as or larger than the inlet size which it would be in your case. i believe youre talking about the flowmaster 80 series, and those actually dont flow very well. but, if youre going for sound, and not as much performance either one will be fine. you might as well just buy the stock replacement flowmaster muffler so you know it will fit.