Flow Rates of some popular mufflers:
 

The following is a compilation of some popular mufflers and their CFM rating. Basically, how good they "flow"...


Dodge Ram OEM: 285-355 depending on year and engine.

Thrush CVX: 260
Thrush Boss Turbo: 297
Gibson Superflow: 311
Hooker Super Competition: 320
Summit Turbo: 331
Flowmaster Super 44: 339
Flowtech Afterburner: 342
Summit Fully Welded: 343
Flowmaster 40: 352
Flowmaster 50: 362
Dynomax Super Turbo: 410
Cherry Bomb Pro: 470
Cherry Bomb Extreme: 500
Thrush Magnum Glasspack: 507
Cherry Bomb Glasspack: 510
Edelbrock RPM: 579
Cherry Bomb Vortex: 580
Edelbrock 304: 640
Dynomax Race Magnum: 711
Borla XR-1: 836
Dynomax Ultra Flow SS: 1000