comes on at 5000rpm, 5300rpm is 1BAR of boost, after that its hard to tell, it comes on stronger than Mike Tyson on steroids. All I can tell you so far is that I have capped the boost at 2.6BAR and have not been beyond 8000rpm (it will rev to 8600). I have a photo of the Turbo on the car but dont know how to post it. For those of you that said at trying to keep it on the road you are quite right it is WICKED mixed with EVIL av it.