Four Valve Technology

Using four valves per cylinder has various advantages:

Less energy is lost during gas exchange, so that power output and torque are higher at all engine speeds. This, in effect, raises the maximum torque value from 222 N-m/168 lb.ft. of the M20 to 245 N-m/ 181 lb.ft. for the M50, while also ensuring higher torque values throughout the entire speed range.

Ideal spark plug position. Flame paths inside the combustion chamber are all equally short, to raise the knock limit. A higher compression ratio can be utilized to increase thermal efficiency and make better use of the energy potential in the fuel.
Reduced moving mass at each valve. Lower (closing) force valve springs can be used to reduce frictional losses while still ensuring that the valves follow the cam contours even at high speeds.