I wonder if the venturi effect has ever been tested in exhusts systems. You have a somthing like a large 3 inch pipe, reduce it down to like 2 inches and then back to 3 inches, this will create a venture effect which will speed up the exhaust gases as they leave acting like a vacum pulling the exhaust gasses out of the engine. Brian 86 16v 98 Jetta Vr6