Stop in for a cup of coffee

Ddaddy said
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

I agree, but of course I'm biased. LOL

Same data shows that even a 2" tube can flow more than the mufflers if it was just a straight run.
2 “ Straight Pipe 283 CFM
2 ¼ “ Straight Pipe 365 CFM
2 ½ “ Straight Pipe 521 CFM

2 ¼” Typical Bent tailpipe 268 CFM
2 ½” Typical Bent Tailpipe 417 CFM

The bends and transitions can add up, especially if badly placed or executed. :(
Only saving grace is by the time the exhaust hits the end of the mufflers its cooled a fair amount.
But even then, this just can't be good.