lenght, diameter, wut thier packed with etc.. all play a roll in how loud or quite a muffler is gonna be. The muffler i have i got off ebay, it weighs about 5lbs. , 13 in. long, but it isnt oval, the tip is thin, all of this makes the sound louder, and yes my car is loud with only changing the mufflers, i have stock everything exhaust wise except the muffler. On my old car i had a oval universal muffler that had a thick tip on it, it waz longer and bigger over all, and it waz very deep, it waz like it produced alot of bass,lol, but seriously, i would start it up in the morning and it would rattle the window where my car is always parked, then i got a new car, put the little straight through muffler on, and that window never rattles but when the car is moving, its loud as crap. sounds good though, no rasp.