Port & Polish (P&P)

What is Port & Polish?

This is what Wikipedia said about P&P: 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.

 Credit to Wikipedia for this info. That is what P&P. But what is pro and con of this process?

Advantages

• Reduce air resistance
• Increase the quality and quantity of the air flow
• Increase speed and pickup (up to 7hp on the wheel after P&P intake manifold)
• It is a very good for street and drag racing setup

Disadvantages

• Power lost when climbing-up hill 
• High fuel consumption
• Sometime can cause an abnormal engine temp especially when climbing-up hill
• Not practical for long distance
• Engine respond very sluggish for daily driven especially during 1000-3000rpm

Head and valves after P&P process

 Tips

• Maximum 2mm port & polish is adivisable
• Before you send you engine head for P&P, try asking the mechanic if he knows about “air flow bench”. It he did not knows anything about that, just forgot them, find another workshop. As Wikipedia says, Air Flow Bench is a device used for testing the internal aerodynamic qualities of an engine component and is related to the more familiar wind tunnel. Or in my bad language, special tool to ensure all the hole (valve hole) that was P&P are in the same size. Different hole size or porting size to the combustion area can cause imbalance compression ratio and cause engine hard to tune-up. Most of the mechanic just use their 6th sense to replace this useful device.
• If you car don't have any problem with power, daily driven and plan to used the engine up to 7-10years, recommended not to do this P&P. If for drag and street racing.. YES!!

Port & Polish Process. Credit to hondatuningmagazine.com for this great picture