BBK Varitune cat back exhaust systems feature BBK Varitune mufflers that have a patented adjustable power valve inside that allows full adjustment of the exhaust flow through the mufflers chambers for a great sound and added performance. This adjustment is made at the rear of the muffler with a wrench by either moving the valve in or out. Once you are happy with the level of sound, it is locked in place with the Varitune locking nut. All of the Varitune power valves are made with stainless steel for lasting durability and smooth operation. These patented BBK Varitune exhaust systems allow you to personalize the power and sound levels of your car 8-10 decibels and 10-15 horsepower. This kit is built with aluminized steel with brushed stainless steel tips. Each Kit is a direct bolt on replacement for the restrictive factory exhaust. Does NOT Fit 1986-1993 Mustang GT with turn downs – See part # 3002