Peformance exhaust mufflers and catalytic converters from Magnaflow Exhausts and AFE Advanced Flow Engineering. AFE Diesel Straight Flow Exhaust Mufflers are large 8" diameter straight flow through mufflers. These Aluminized steel or 409 stainless steel mufflers do a good job of letting the air out as well. The design allows you to have the option of turning the muffler around for better flow or a quieter ride.