Needs a tongue in cheek smiley.
I'll not withdraw earlier post, but idea is total codswallop.
I agree.
If the valves are inlet then the compression stroke pushes gas back into the inlet manifold!
If exhaust valves then compression will be lostthere as well. Air/fuel mix will be pushed into the exhaust manifold/exhaust and end up igniting in the exhaust/cat
Gasflow is quite complex.
Read Modern Engine Tuning
By Graham Bell. He covers it pretty well.
The guru on gasflow is David Vizard.
Polishing exhaust ports will help as well as matching them to the exhaust dimensions. Inlet porting is even more complex due to the shape of the inlet side and getting good mixing/flow. It has been described as an artform with experience the key. Port volumes are measured and matched etc. Flowmeters used to match/measure air.
