Originally Posted by Steven_RW
How can early intake valve closing allow MORE mixture in that results in a high compression issue and increased pumping losses. Surely shutting the intake valve early will allow less in and therefore less compression issue, less mixture to create pumping losses?
My thoughts are this is a typo and the line should read " Another problem with LATE intake valve closing "
RW,
I think what is being said, is that due to an inlet valve closing earlier than normal, as the engine moves onto the compression stroke from intake stroke BDC, then effective volume within the cylinder is greater when the valve closes early (since if the inlet valve was left open slightly longer some induction gases would be lost through the inlet valve to aid cooling but also reduce the compression volume).
This has the effect of increasing the compression pressure within the cylinder as well as increasing pumping loses since the piston is trying to compress more volume than normal.