Combustion Chamber mod.
I ussually never care ennough to remove a cast to unshrouded the valve (i just remove the sharp edge arround the valve seats) ,and not care ennough with open chamber (same chamber diameter with the bore) modiffied. Because earlier before , i always think it was a merely jobs that would reduce Compression ratio.
Now i have finish one of my cylinder head that the valve was totally unshroud ,and open chamber... a more free breather than my old cylinder head...
But with that head i only could improve the maximum compretion ratio to 10.8 : 1. And my old head make it to 12:1 (cannot make more than 12:1 because the handicapped piston, strooke ,etc).
And a few more day was my day to race it !!! I wouldn't have a chance to tested between that 2 heads one by one ,even as to dyno-ed it one by one.
Gimme advice wich to go between that 2 cylinder head
-A bit free breather with smaller Compretion Ratio ,or
-Bigger Compretion Ratio with a bit breathless