This is the Flowmaster two-chamber Series 40 muffler for classic Mustangs. If you like a throaty roar, the original two-chamber Flowmaster muffler, available from Virginia Classic Mustang, is for you. Be advised, these guys are loud with a lot of interior resonance. But you just can't beat the demeanor of the Flowmaster. Available in 19- and 23-inch lengths with two different types of pipe offset, they're a good fit for '65-'04 Mustangs, including '74-'78 Mustang IIs. All you need is a good exhaust shop that can do custom pipe bending.