See “Metric Mechanic HiFlo ST M3 Head” chart on the next page. By using stock cams and porting, the engine ends up with a very flexible power band on the street. Stock camming also helps the engine pass emissions. Metric Mechanic 29.5 mm M3 Intake Ports compared to stock port sizes which are about the diameter of a quarter. MM Surface Turbulence valves with Manganese Bronze valve guides. Valve Springs: Our springs are taller with a slightly reduced wire diameter.
The stock spring exerts 78 lbs. of pressure on the valve seat and 185 lbs. on the nose of the cam at full lift. Our MM valve increases the seat pressure to 90 lbs. Exhaust Flow : On a well designed engine, exhaust flow would be 85% of the intake flow. On the stock M3, exhaust outflows, Timing Chain Assembly.
