yeah they do but they do there tests at sea level im almost 3,000 ft above sealevel, so my compression is 180 psi per cylinder, the higher in sealevel youll actually lose 7psi per every 1,000 ft u go up in sea level, so if i was to take my ski somewhere sea level ill prob gain psi and prob have to run way higher octane. i actually got the head from jetmaniac, and hes from florida and he said he was running 93 octane with this head at daytona. so that kinda confusses me. i dont really understand the whole octane and compression thing, i think the higher octane u run will actually make your ski run cooler, and not have to work as hard. maybe someone can school me on this.