There are many examples of current OEM vehicles out there that make 330-350HP through SINGLE 2.75" or 3" exhaust systems. And I've seen several supercharged F-bodies pushing 450-550 rwhp and running high 10's/low 11's through single 3" systems. I don't think your 302 is gonna require a dual 3" anytime soon.
Thanks everybody. Actually, I am looking into a 347 for the "near" future and am wondering if 3" exhaust is recommended. So Flowmaster and MAC make 3" catbacks, how about the H or X pipe? Also, do most 347/351 guys run 1-3/4" LT's or are 1-5/8" acceptable?
even with a 351 i would go 2.5 or 2.75. 3 inch is usually good for cars pushing around 600hp. So yeah like said above, Mac, Flowmaster and i think another company make it, you wont need it until you are around that hp range.