I just had my exhaust done the other day with this setup. RKsport ported 4-2-1 header, custom 2 1/4 header back exhaust with a no name 2 1/4 high flow cat, and a tanabe muffler. Car runs great but sounds like a fart can. I have no resonator and that be the reason for the farting. What resonator would be good for it and what length should i get?

I have a Cherry Bomb glasspack, 22". No complaints whatsoever (and it was cheap in price)

I bought a 4" round Magnaflow stainless steel muffler to use as a resonator. It really wasn't that bad as far as price and it doesn't rust.

^ ditto... I used a 20" long (or so) 4" Magnaflow resonator... works minty for killing the raspiness.

Any round bodied, straight through muffler will reduce the raspiness without any effect on performance, as long as you maintain a constant insde diameter and has a perforated core, not a louvered core. A louvered core will look like a cheese greater on the inside(disturbs the exhaust gas flow), while a perforated core look like holes punched in the sides(nothing protruding into the gas flow). The longer it is, the more it will tone down the exhaust sound, upto the point it will be slightly louder and deeper toned than a stock set-up (this depends upon the types of mufflers used).