I am no expert on head flow for sure.As I understand it ,if the valves are not sunk as much as the head. Is milled,they will come in contact with the piston.I have not heard of a replacement piston that will increase compression for this engine,Maybe there is one available? If there is that would certianly be worth looking in to,but I would think a dome type piston would still contact the valve.I have high pressure springs that will work after the valves are sunk.The valve Stims would have to be trimmed to keep the geometry correct.I understand how all of that works.What I don't understand is how it would affect the air flow enough to off set the gain from the compression increase.I maybe wrong ,but I would think these engines were lower compression,because they were coming from a early design ,that we're made to start by hand crank.As electric starters proved to work,the compression increased,and air flow and engine design got better.
