Originally Posted by unclemat
So it seems that most folks who port their stock manifolds are actually hurting their performance (most run < 400 whp setups anyway).
I think that anything you do to aide flow in or out of the motor is going to have some effect on VE. Meaning that it will aide the complete filling of the cylinder with a fresh charge on the intake stroke and aide the effacuation of spent exhuast gases on the exhuast stroke. Doing minor porting on the intake manifold or TGV housing is going to have a nominal effect on a car for example which has a restrictive exhuast and for example the stock turbo inlet hose.
An engineer can work with the laws of physics and caculate the effect of various bends, changes in pipe diameter and other restrictions on the flow rate and how much heat is added in the process.
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.