will iguess i have a question for clocked work now or some one whon know the ansew. I was looking on your site and there is a page on the about head shim and how to get proper clearnce.i understand the math part but the reason im righting now is why do you need it to make sure you piston not hitting the glow plug or cause you run a different percantage of fuel? cause latly i been seeing post about head shims and fuel from going to 20 to 30 if you need to shim up or down but know seem to ansew these guys at all. And how do you end up with a pitted head ? i hve not seen one yet and i been in this 3 years mostly basher but know racing for a full seasion i hope since i started racing last year the last two month and i did pretty good with it too so bashing gone for me i want to know my engines stuff for racing i kinda like the os 25 but hard to see the chart on what you did for it.