Have just fitted a N75J valve last night and am happy with the performance different. I am not too sure how much power (if any) changing the valve actually gives you, allthough it seems as if there is something extra in when in the turbo range. However the biggest noticable difference is how much smoother the engine is from 3000-6000 revs. It seems to hold to boost right up till 6000 much better than the stock valve which makes it smoother and seems to enable you to change up gear later than normal. As I only fitted it last night (bit of a twat getting the clamps off) I have only done 60 ish miles and havent encountered any negative aspects yet i.e. going into LIMP mode. But on the whole I would say best money to performance (only £40) I have spent so far on the car.