Unfortunately my compression tester would not fit between the head and frame on the GG. All i can tell you is even with 20% 110 race fuel it still pinged like a jar full of marbles. Plus it would overheat warming up in the driveway. Never overheated until i put the new head on, even in the nasty tight stuff in summer in Arizona. It did have nice low and mid though. Oh yea, it spooged like the Valdez. RB designs fixed my 16 yz 250x by simply correcting the squish. Bike ran great, clean and easy to jet. Thats all i wanted for my GG and even wrote that in my shipping box and emails. The only way i could get the GG to stop pinging was to go back to stock jetting, which was a blubbering pig and go 1 step richer still on all the circuits. The bike stopped pinging but spooge was even worse. By this time i was fed up with it and ordered a 19 head, stock, which was on back order. Then i decided to just sell it, which was amazingly easy. Told the new owner the story and deducted the price for a new head in the price of the bike. Both of us were happy.
On the plus side service was quick from RK, by the time they answered my phone calls the head wad already on its way back to me. On the minus side it certainly failed all my expectations.