Most flowmaster's don't flow that well. Most people like them because they don't wear out, and they have an unmatched sound. I believe the race flowmasters flow pretty good. If you're looking for flow, the turbo mufflers work good, magnaflows, Dynomax Ultraflows are good as well. All of these have packing in them and will eventually wear out. In tests they usually compare the mufflers to a straight open pipe... standard flowmasters have been tested at 40% vs. open pipe, turbo mufflers can flow as well as 90-95% vs. an open pipe. They still have good sound control as well.