Re: Flowmaster 300 Series Vs 400 Series
Personally, I would do X-pipe, that's what I run. It's got a little bit smoother tone to it.
RE: Flowmasters, I've had three different Flowmaster setups on my '68 w/454, using Hooker Super Comp 2" headers into 3.5" Spintech x-pipe, then reducing into 2.5" mufflers.
My first set was American Thunder 40 series system, with tailpipes exiting right behind rear wheels. Way too loud, so I went to full tail pipes. Still loud, but better. Interior resonance was awful in both setups. Finally I tried their longer three-chamber 50 series Deltaflow, which did reduce interior resonance some, but not much. Exterior sound was great, but inside was just too much. I have taken the Flowmasters off and have some new Magnaflows to install, hopefully they will drop the interior resonance level to a minimum.
Flowmaster tech explained to me how the sound waves bounce off the baffles and then back up into exhaust system, creating "resonance" at certain rpm's. Apparently no amount of soundproofing will inhibit those sound waves from reaching interior. Seems to be a function of exhaust size and pipe length. I ride in a buddy's '69 396 Camaro and he runs 40 series Flowmasters with very acceptable interior resonance levels, probably because he has smaller headers and exhaust pipes.
My advice, maybe you'll get lucky on first shot, but be prepared to experiment with mufflers to satisfy your own personal taste in noise levels, both in and out of car. I would use some easy-disconnect clamps and make sure you're real happy with everything prior to welding the whole system in place.
Dave F. in Rhode Island
'68 Camaro SS Accel DFI 454 (SOLD - I'm a boring Corvette owner now)
Bought my first big-block Chevy in 1970