Originally Posted by alfriedesq
From a lay person's (like myself) perspective, the whole concept can be simplified by thinking of a turbo charged motor as an air pump. Everything you can do to aide the free flow of air into and out of the pump will allow it to process more air. The more air you can flow the more fuel you can burn and the more energy that can be yielded from the combustion process.
Apparently more is sometimes less as this test shows. I don't know what the manifold changes (air velocity due to increased volume?) but clearly it's not helping but hurting here. Similarly I believe porting heads is not a good idea at lower power levels as it may hurt spool.