Porting (engine)

Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve the quality and quantity of the air flow. Cylinder heads, as manufactured, are usually suboptimal due to design and manufacturing constraints. Porting the heads provides the finely detailed attention required to bring the engine to the highest level of efficiency. More than any other single factor, the porting process is responsible for the high power output of modern engines.

This process can be applied to a standard racing engine to optimize its power output as well as to a production engine to turn it into a racing engine, to enhance its power output for daily use or to alter its power output characteristics to suit a particular application.

Daily human experience with air gives the impression that air is light and nearly non-existent as we move slowly through it. However, an engine running at high speed experiences a totally different substance. In that context, air can be thought of as thick, sticky, elastic, gooey and heavy (see viscosity). Pumping it is a major problem for engines running at speed, so head porting helps to alleviate this.

When a modification is decided upon through careful flow testing with an air flow bench, the original port wall material can be carefully reshaped by hand with die grinders or by numerically controlled milling machines. For major modifications the ports must be welded up or similarly built up to add material where none existed.

The Ford two-liter shown above in stock trim was capable of delivering 115 horsepower@5500 rpm for a BMEP of 136 psi. Contrast this with the ports shown below.

This aftermarket racing GM Pro Stock head was capable of 1300 horsepower@9500 rpm with a BMEP of 238 psi. Since BMEP is an excellent efficiency measure and closely related to volumetric efficiency, the aftermarket Pro Stock head is vastly better than the stock Ford. In fact a BMEP of 238 puts it near the top of the racing engine world. It is close to the limit for a naturally aspirated gas-burning engine. Formula 1 four-valve/cylinder engines typically achieve BMEP values of 220 psi.

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Wikipedia