Here's a little something I found tonight. Muffler flow chart.
Coming from
http://www.allfordmustangs.com/forums/4-6l-tech/4609-muffler-flow-chart-why-flowmaster.html
Enjoy
Muffler Flow Comparison Chart
Shown below are competitive mufflers versus DynoMax Ultra-Flo SS and Race Magnum Welded models. For Powertech Index cold-flow testing, the pressure drop across the muffler is held at 20.3" H2O and the flow rate (scfm) is recorded.
MODEL (Flow Rate- @ 20.3" H2O) Muffler Inlet Size
+ Edelbrock 5501 492 scfm 2.25"
$ Flowmaster 42440 483 scfm 2.25"
Race Magnum Welded 17216 711 scfm 2.25"
+ Edelbrock 5511 579 scfm 2.50"
$ Flowmaster 42540 352 scfm 2.50"
Ultra-Flo SS 17263 1133 scfm 2.50"
Race Magnum Welded 17218 1000 scfm 2.50"
# Borla 40600 836 scfm 2.50"
+ Edelbrock 5505 708 scfm 3.00"
$ Flowmaster 43040 392 scfm 3.00"
Ultra-Flo SS 17296 2200 scfm 3.00"
Race Magnum Welded 17220 2200 scfm 3.00"
# Borla 40450 1400 scfm 3.00"
# Borla 40575 1100 scfm 3.00"
@ Edelbrock 5535 562 scfm 3.50"
$ Flowmaster 435409 576 scfm 3.50"
Ultra-Flo SS 17268 2200 scfm 3.50"
Race Magnum Welded 17224 2200 scfm 3.50"
# Borla 40615 854 scfm 3.50"
@ Edelbrock 5537 1400 scfm 4.00"
* Flowmaster 54040-10 634 scfm 4.00"
Race Magnum Welded 17225 2600 scfm 4.00"
# Borla 40741 1450 scfm 4.00"
+ Edelbrock General Application Series
@ Edelbrock Victor Series Race
$ Flowmaster 40 Series ( 2 Chamber)
* Flowmaster Delta Force Race Series
# Borla XR-1 Racing Series (Round or Oval)