3.5” or 3” collector
 

Hello everybody I have a question if anyone wants to answer. I have a 69 gto. It has a 428 with 270+cfm 722 heads. It has a old faithful cam with Crower solid rollers. Has a sd performance real ram air IV cnc style ported intake. Max a lite connecting rods with je pistons. 10.5 compression. 4 speed M22w with 3.73 gears. The headers are 1 7/8” Indian adventures headers with 3.5” slip on collectors and a 3” exhaust with x pipe and dynomax ultra flow mufflers. Just wondering if changing to a 3” slip on collector would pick me up some torque? My thinking is first of all the exhaust slows down a bit in the large 3” collector them reduces abruptly to the 3” exhaust. Wouldn’t the stranger flow from the 3” collector to 3” pipes work better? Idk. The car works great but you know how it goes. Can never leave these cars alone.

I can only speak from experience. When I went from 1 /34" w 3" collector to 2" w 3 1/2" collector my car went faster in the 1/8th. I want to connect my 3" exhaust but a tapered 3.5-3 reducer and the X pipe I have and reusing my Walker dynomax mufflers doesn't appear to fit. Engines no way as much as you have. Been 12.0 @ 110 in 1/4 with old headers.

I ran 3.5 to 3 with reducers Dr Gas X into 3" system. Flanged the reducers at both ends.

How long are the reducers? Mine are about 12". Was trying to not have an abrupt reduction. I have the Pypes X pipe. The Dyno max mufflers are pretty long, may have to get shorter. Also my headers are longer than most off the shelf ones.

Mine were about that long also. I think flowmasters and pretty thick tubing also. Also made it easy to go open headers. had front brackets to hold the rest of the exhaust up