The theory is; after the gases leave the head, and get 6" out, then there not that much back-pressure, as the engine want's some back-pressure.
This ought to stir up opinions, lol.
yea right.... every car i've ever owned goes faster has responded to bigger exhaust.
i run straight 4" on my dart into 2 chamber flowmasters with no tail pipes (you wouldn't think that would create backpressure). pull it off the car instantly picks up a tenth & 1/2.
my challenger with a basically stock 360 in it (13 sec car) picked up 3 tenths when i chopped the 2 1/4 tail pipes off.
440 in my belvedere, ran 12.20's with 3 in exhaust no tail pipes. stepped up to 3 1/2" and the car went 11.90's.
that back pressure theory is absolute crap if you have your car jetted properly. using exhaust for proper scavenging is a different story.
