Ok. NOW I'm helpin my friend look for a blow off valve. We found 2 models, a Type S blow off valve and a Type H. What the hell is the difference?

the psi rating I believe...one can take more or something like that...type S is for about 12psi or less...and type H is for 10-25psi I believe. So it all depends on what the turbos psi is at...hope it helps man... And type H racing is for about 10-35psi...peace.

Ok thanks. That helps somewhat.

To be honest the designation givin by greddy for their three blow off valves is just to seperate the three. The S is standardly used on road going cars with dump tubes (return lines going from the BOV to the turbo inlet) that are running less than 1.8 bar of boost pressure (under 26 or so psi). The H is a louder and more quickly actuating BOV that utilizes no dump tube. The H can with stand 26 psi of boost also. As far as Greddy's racing type blow off valve...it is just that. Designed for used on 700-1400hp cars running in excess of 1.3 bar on low boost settings. The Racing type is not good for street cars...I hope this helps...by the way many other companies manufacture and/or sell other types of blow off valves. Blitz, JUN, HKS, Apexi, etc. all offer great (but equally as functional) alternatives to the Greddy BOV line.
Later,
Dan