Here's the way Flowmasters work:
THEY SOUND GREAT, but-> less chambers = more sound
My dads 79 Big Ten has dual 40-series 2 chambers, the sound is sweet and he picked up about 7 extra horses.
My brothers 88 IROC-z has a single 1-chamber where the cat should be, and he picked up about 12 horsepower and a couple of noise-ordinance citations.
Just some thoughts