mufflers

FWIW, the advertised air flow numbers of a muffler are the last thing you should consider when choosing a muffler. It's the easiest parameter the manufacturers can jockey with to meet their marketing goals. Air Flow is only valid and meaningful if it's given with the pressure drop the number was obtained with. Since there is no mandated test process for muffler air flow that defines a standard pressure drop air flow numbers between manufacturers are useless and even within a manufacturers line of mufflers I wouldn't be surprised if they change the test to get numbers to match the marketing goals.

An example would be manufacturer A tests their mufflers at 1 psi pressure drop and manufacture B tests at 3 psi. A advertises 400 cfm of air flow and B advertises 500 cfm of air flow so you would think B is better but if you were to test A at 3 psi pressure drop it would flow 600 cfm or more a than B. These aren't real numbers just to show how not having all the info you can't compare.

Any perfromance muffler properly sized for the application has the capability of flowing more than enough air to support the engines need without creating a restriction.

Just pick your muffler based on sound, material, gaurentee, workmanship, fit, etc.