I have a custom exhaust setup, a hotshot header running to 2 1/4 pipe i had bent for me at a local shop. im not running the resonator, just a magnaflow muffler.... you wont lose any hp if you remove the resonator, you will probably gain a tad... as for noise, its a little louder, but not by much. Hell, i was running my car with no restriction whatsoever at one time, header to a testpipe that replaced my cat, on back to my magnaflow... and it still wasn't obscenely loud.... i say go for it, rip that thing off
