This equation shows that the surface finish or wall roughness height is a function of the friction factor. The friction factor generates the shearing the force on the outside of the pipe which affects the final velocity profile, therefore restricting the velocity of the air / fuel mixture within the ports of the cylinder head.

The following equation has been developed for calculating the frictional head losses due to the friction factor. Frictional headloss is the loss that occurs from loses in pressure within circular pipes due to the surface finish of the internal diameter. It is the result of viscous dissipation converting mechanical energy to non-recoverable internal energy plus heat transfer.

The Darcy-Weisbach equation:

It can be seen from the equation that the greater the friction factor the greater the frictional headlosses or pressure drop. This restates that a pipe with a rough surface finish will encounter the same pressure drop as a smaller pipe with an improved surface finish.

It has been extensively proved that the introduction of alterations within a pipes internal geometry, bends, contractions, ect, results in losses, as shown below. Head porting minimises these alterations, and therefore the associated losses.