The Treadway car uses basically a stock system, and I opted to follow suit. In our case, we used an S4 downpipe (modified, see below) leading to stainless flex pipe, coupled to an aftermarket racing cat, back to the stock exhaust system. Not elegant, but effective and cheap. Other options would include: 1) Buy the factory S2 dual system. This would require multiple underbody panels, a Very Big Deal. 2) Have a dual system fabricated. 3) Bring your car to Graydon Stuckey, have him build a 3" stainless system for you, and retain the measurements so the rest of us can mail order our systems from him. 4) Apparently Scorpion makes a 3" singly pipe system for the S2. Davy Jones at Revsport is adapting this to the Ben Garret car.