I'll try and keep it short. i replaced my n75 valve last week due to fluctuating boost and it seemed to sought it out a treat my mate put it on a wideband and seemed to be fueling great too. it was ok for about a week but for the last few days its taking alot longer to start sounding a bit chocked up but when started its fine. i dont normally take it past 5000 rpm but i gave ut a bit a few nights ago and when it got to about 5 grand it seemed to hesitate then started to backfire like it was on the rev limiter and chucked out a cloud of black smoke, tried to take it past 5 grand a few times now and the same every time. sorry for the long thread just gettin the ump got to replace the clutch and flywheel this weekend along with bushes and sought the windows seemed to come all at once. i would love some pointers many thanks. ps the car is revo stage 1 de cat forge front mount no mods out of the ordinary.