Help me understand cam timing, advancing or retarding a SOHC for mpg

[cRiPpLe_rOoStEr]

Originally Posted by Madmanmax

In theory if you had direct injection you could keep the intake valve closed to increase vacuum in the cylinder so that when the fuel was injected it would vaporize and then you could open the valve to mix in the air. this could drastically increase burn efficiency.

IIRC some trims of the Volkswagen 2.0 TSI engine close intake valves earlier, in order to decrease heat irradiation.