Originally Posted by wanderer1955 1st
You could have them on backwards , It will make a big difference ..

Originally Posted by Hot Rod John
I emailed Speedway and asked if Smithy's internal louvers are directional. I'll post their response and then we'll all know for sure. thumbs_up
Per email from Bill Emberton 08-08-2014, Street Rod Tech for Speedway Motors: "We pulled the muffler and the latest versions have an inlet arrow showing flow direction of the muffler."