do you mount it right before the muffler, or on the intermediate pipe from the cat? I have a vibrant catback and I want to install a resonator but an 18" resonator seems too long to mount in either pipe.....maybe a shorter one,,,,,would it hurt to run 2 smaller ones? further deepen the tone?
Put your resonator right after the cat. The longer the better. I have a 29 inch res on mine.
your 18" will fit fine right after your cat. Hell I have a 22" one right behind my cat and it fits....