360 la headers & straight pipe
Ok wait, he has straight pipes? A muffler won't make it louder, then. Whoops! I just had took a short nap. Probably fogged out still.
Sound is weird. A 'muffler' can actually louden an exhaust..
Tone has a lot to do with it too. Certain tones can have the same SPL (sound pressure level), and yet feel or sound quieter. Change the tone, and even at a dB lower it can 'sound' louder.
Wave reflections can amplify this, and the way the classic flow masters are baffled, they do exactly that.
Of course, it all depends what's making noise. A low compression, small cammed 360 with proper timing and AFR will be pretty dang quiet. Fatten the AFR, retard the timing way back, and it'll start to sound like a Harley.
Better yet: put some flat tops in it, get it to 11:1, cram in about
[email protected] on a 105-106 LSA and it'll sound bitchin no matter what kind of exhaust is on it.