ive got a brand new n75 which helped as it would not even peak at 21psi as it should with old one, but them race valve of which you speak are just a rip off as its just a h valve from a 2.7 twin turbo audi iirc, with a sticker on them and they charge 20 + quid more. mine got mapped on the standard valve (C) and was fine and now i have (F) which replace (C) valve at vw.