Stop in for a cup of coffee

As far restriction goes, I think the flow bench comparison is probably about as consistant of a test method as can be done. And even that, depending on whose doing it and the procedures...
Good data in the thread and exactly what I was saying.

2 ½” 8221; Inlet/Outlet Flowmaster ( 2 Chamber) 249 CFM
2 ½” 8221; Inlet Outlet Flowmaster ( 3 Chamber) 229 CFM
2 1/2" Inlet/Outlet Magnaflow 284 CFM

MagnaFlow has 20% more flow than either of the Flowmaster configurations.


It also produced a little more peak HP. The dynamic range wasn’t tested, but it’s likely a larger differential at lower RPM.

Magnaflow 372.8 HP
Flowmaster 369.4 Hp