The single most restrictive part in an engine is within the cylinder head. Get the flow of air and fuel to easily pass these restrictions and you are on your way for more power. This is a great subject to cover so we need to split the subject in convenient parts.
We are mostly going to concentrate on the cylinder head only and leave the induction and the exhaust system alone and maybe in the near future we can look into them as well as they are very important too.
Now back to the cylinder head, first we must establish the area of utmost limitation to flow. We can’t just start grinding everywhere in the cylinder head as air moves the way it wants and not the way we want and this is very important or you can ruin the cylinder head.
If we look at a port from the side, and we divide this port in three parts we see that if we look at each part alone we determine that each of them has different flow characteristics so let’s take a look.
First part is the main body or what you see when you look from the inlet manifold side. This is the least restrictive part but the most abused from the amateurs.
Then as we go further to point B we start to close slightly and we encounter the valve guide boss and the port starts to turn and here the restriction starts increasing.
Then Point C, the most important part, here we encounter the valve and apart from the valve which is in the middle of the port, the valve also open and closes and when the valve is closed, flow is equal to zero and this determines the greatest restriction that any single cylinder head has and here is where we concentrate our efforts to pick up the airflow when we port the cylinder head.
