ive tried all n75 valves H J F and C and the only difference in all of them was the J gave more boost in lower revs range apart from that nothing at all
Looking around google it seems that it might actually just be the H version of the n75 which came on a 5cyl audi. Its more aggresive than the J. One guy had the full part number on his when he got his valve from ECS and alot of other people on different forums are saying its the H version aswell. There was even an ancient post from here that said about it.