im having this issue, its fine no smoke on startup, no smoke driving or coming on boost but if you say do 40mph in 3rd let the revs drop and then touch throttle a big cloud of greyish smoke comes from the exhaust, if i sit revving the car no smoke can be seen from the back of the car and idle shows no smoke either. i dont think its valve seals as you said it doesnt smoke when started up, anyone else have any ideas what it could be?