Go with Kibblewhite as to they designed a custom set for me and has a complete Spring and retainer set for the Kawasaki ZX-10's ranging from 04-09 year models, specs are all the same for the spring and retainers. Retainers are lighter than the Factory sintered aluminum ones which are already very light. The retainers are Titanium and the Valve Springs have increased seat pressure. The seat pressure is just enough to keep them from floating at high RPM's and when using nitrous and not like some of the other race springs that has a ton of seat pressure which ROBS horsepower. Call them and ask for Warren Fong and let him no that Marcus Thomas referred ya....