[Moderatoir Note: It's okay to discuss what's legal and what's illegal, but it's NOT okay to discuss "How to do illegal modifications." - Mike Substelny, DML moderating team] free flow exhaust is legal as long as it isn't too loud. "open exhaust" is illegal. i have borla exhaust on my mustang and that is free flow exhaust. it will pass emissions as long as your converter is still connected to your car but they will never know if you take the converter off the car after emmissions... he he he. mark nbrommer2k wrote: > What is the legality of such a free-flow exhaust in the US? And what > kind of repercussions would such a system have on emissions tests? [moderator snip]