3 inch piping
 

i have 2 chamber flows......and thursday im dumping them for some spintech mufflers and 3 inch oval piping, i know it will sound nice but will i lose alot of torque???? i have a mostly stock mustang....but the thing isim planning on adding hthe power adders such as headers and intake and gears and stuff so should i just go for it and get 3 inch or get 2.5....and how much sound will i sacrafice if i get 2.5 inch rather than 3 inch??????????

IMO, 3in would be too much. I had a 420HP Chevy 350 in my truck and I just barely needed the 3in full length pipes.. If you go too big on piping your exhaust will lose velocity and will "hang around" in your pipes, you want the air coming in and leaving very quickly. Also, you are correct in stating that if you lose enough back pressure you will lose some performance on the low end, but I believe it will gain it at the top end. I would say an H-Pipe with 2.5 in is more than adequate.. Just get some Hi-Flow cats and mufflers and you shouldn't out grow it for a long while.

Exactly

leave the e inc h pipes for the diesl engines and rice burners you need back pressure if you had a turbo it would be another story