does the use of different cams increase the potential for contact because of higher lift, or does a different open / close time increase it? by sitting the head on the block with a used gasket i can lift the inlet valve 4.2mm at tdc before contact. havent yet machined pistons but have 72.5cc total volume using 1mm gasket (looking for 81cc = 7.2cr). it would be pointless to pocket pistons if unconditional clearance could not be achieved but if each pocket was bigger than 81-72.5 / 4 = 2.1cc, cr would be out, then i'd need to skim block to recover cr and this would mean that the pockets should have been deeper!!!!! does anyone know the reqiured mathematics to calculate pockets or can i get away with a simple skim of the piston if i'm careful with cam set up etc