The end caps are interchangable, both come with spark-arrester screens, there is the pea shooter (~10mm opening) and the racing end cap (~18mm). But does anybody know the differences inside the mufflers themselves? I've got the street legal muffler from the previous owner clean and unused, lying in my garage. It appears to be polished steel or even stainless steel. Does it have a catalytic converter inside, to match the Lambda sensor in the street legal header? Does itself restrict airflow or just the pea-shooter end cap? Anyone go an idea how it sounds? Maybe someone here is runn his WR street legal I'm reluctant to simply try it out as w/o resintalling all die lambda-O2 sensor stuff and enabling closed loop operation any test would ruin the catalytic converter.