I also would be interested in the exhaust system, as in my world it is " Only Air & Fuel " As per the sticker on my back window of my Driver #765 77157 miles so far, as up here in The Great White North it is summer just for like 6 months LOL I like my Focus RS but another 100 hp would make her slide around corners LOL Thank you PS My driver has Borla headers and muffler LOVE the sound.