2003 coupe 6sd w 350z pipe ans k&n drop in, test pipes, y pipe stock ecu. No oil or coolant loss in the 25k miles I put on it. The car has 78k total miles. I drive 95% highway cruise control 4k miles amonth. When I floor it in 1st black soot comes out only in 1st then it's fine. I floor the car like once a week but it only smokes the first pull and in 1st gear. I repeat the process and nothing for days, but it worries me to see a visible cloud in my rear view.

Probably due to the test pipes

Welcome to having no CATS. You should see the garbage on my garage floor.

Ok so I need not worry? I wasn't thinking it was engine related

Not at all. It's just carbon from built up crap that you're Cats used to catch. Just don't blow that in front of a DOT officer.

thanks for the tip! Thanks for helping me out guys.

Do high flow cats give the same effect? I'm gussing less than test pipes