An improved cast cylinder head for a high performance internal combustion engine is provided by an especially configured quench surface from which a contoured combustion chamber extends having a metal mass buildup shrouding the exhaust gases through the exhaust valve seat. A metal mass buildup configuration is also provided about the intake valve seat which acts in conjunction with an especially configured and proportioned valve intake passage to draw the fuel-air mixture into the combustion chamber in an unshrouded, helical flow pattern. The intake passageway configuration is such that a rich fuel-air mixture is drawn through the intake valve seat at a portion thereof remote from said exhaust valve seat while a lean fuel-air mixture exits the intake valve seat adjacent the exhaust valve seat. Positioning the fuel-air mixture in such a manner in combination with the unshrouded metal mass buildup minimizes short-circuiting of the fuel through the exhaust valve seat in a valve overlap condition.