first off, MT, you know i'm not trying to be a dick or anything, but please put some sort of pipe out to the side, or out the back... dangerous from fire, which is a VERY REAL danger on a turbo car, you might be more concerned if you could see the foot of fire coming out of the pipe when you downshift, etc..... might not do it in the driveway, but with a load...lookout!
danger of CO poisoning. you won't know it when it is happening... no smell, or anything... if you can smell fumes at all, then you know you are getting some CO in the car with you! and that is BAD NEWS. you can overwhelm the built in ventilation of the car....you could black out behind the wheel and not even know it was going to happen....
just putting that out there, not making this stuff up...