A port and polish job is one way to increase the power output of any internal combustion motor. Many people have heard the term before but fewer people know exactly what a port and polish job is or what it does.
Port and polish work is a relatively simple process and it adds power because of some relatively simple principals. First, we’ll look at what exactly port and polishing is and then how and why it adds power output when we port and polish a motor.
Port/polish work is a relatively simple process that is performed on the engine’s cylinder head. First, the intake and/or exhaust inlets (ports) on the cylinder head are enlarged using a grinding or cutting tool. This extra room helps the engine to draw extra air into and out of the cylinders, mixing it with more fuel which means more power. The enlargement of the inlets is what is referred to as “porting”. The next step in the process is polish work. The enlarged ports are then smoothed over using a sanding or grinding tool. This removes flaws and/or obstructions from the surface of the inlets, allowing air to flow more rapidly into and out of the cylinders. This process is called “polishing”.
Port and polish work helps the engine to make more power in three different ways.
By making the intake ports bigger, port and polish work removes restriction from the intake stream which makes it easier for the engine to draw in fresh air. The more air that is drawn into the engine, the more fuel can be mixed with it and burned, resulting in more power.
Removing imperfections in the surface of the intake tract reduces air turbulence in the intake port which allows air to enter the cylinder at faster speeds. These faster speeds not only allow the engine to breathe easier, they also help the fuel to mix with the intake air more completely once inside the cylinders, which increases burn efficiency.
Finally, a port and polish job can have the same effect on the exhaust stream as it does on the intake by removing restriction and increasing the flow capacity of the exhaust ports. The engine can rid itself of spent exhaust gases more efficiently, thus by reducing what is called “exhaust backpressure”, port and polish work helps decrease the amount of work your motor has to put in to getting rid of spent fumes.
Once you understand the process of port/polish work and the results of this modification, it’s easy to see how it helps engines make more power by increasing the efficiency of the intake and exhaust streams. Now let’s take a look at how you can do yourself!
Of course, the reason automobile manufacturers don’t port and polish during the assembly process is that, as you will learn, it is very time consuming. Computer Assisted Design has improved the shape of stock cylinder heads in recent years, but there is still some “free” horsepower and fuel economy to be had by “cleaning up” the intake and exhaust ports as well as removing some of the sharp edges from the combustion chamber as well.
Since an internal combustion engine is basically an air pump (and the more air you put in and take out, the more horsepower it makes, and the more efficient it is) the “free” horsepower provided by the porting and polishing operation makes more sense.
First of all, you will need good eye protection. You will also need an air compressor and an air-operated, high-speed grinding tool. It is recommended to use 80 grit sandpaper rolls to smooth the surface and match the ports to the gaskets. 80-grit sandpaper provides an excellent surface finish that is not too smooth and not too rough for the air/fuel mixture. In fact, a good port and polish job adds an additional 10 percent in both horsepower and in fuel economy, so it’s worth it.
Start by cleaning the ports and then painting them with layout fluid. Place the high-performance intake manifold gaskets and exhaust gaskets in place and secure them with the bolts or nuts. Use a scribe to mark the areas to be matched. Now remove the gaskets and use the rolls of 80-grit sandpaper screwed onto the mandrel attached to the high-speed, air-operated grinder to match the ports to the gaskets. Take it easy. If you remove too much material, you can ruin the cylinder heads.
If you need to remove a lot of material from the cylinder heads, it is recommend using a more aggressive tool in the die grinder, but be careful. Use the 80-grit sandpaper rolls to finish the port and polish job. As the sandpaper rolls begin to wear out, replace them with new ones, but do keep a couple of the tapered rolls for use later. Use the short mandrels with straight sandpaper rolls for areas near the outside of the ports, and use the longer mandrels with the tapered rolls of sandpaper for the inside work.
Now use a worn tapered sandpaper roll mounted on a short mandrel to polish the inside of the combustion chamber. Be careful not to damage the valve seat area and not to remove too much material as this can cause a loss in static compression–which can in turn, cause a loss of power.
When it comes to porting and polishing, less is more.