Stop in for a cup of coffee

Mattax said
Vizard flow tested a bunch of mufflers back in the 70s - published the results a few places including Performance with Economy.
Glasspacks generally flow much better going with the louvers than into them.

toolmanmike said
That's because they are a straight through tube. :rofl:

They may flow the best, but they are very loud...

Turbo mufflers are a nice compromise with quietness and flow....