Piston Deburring

[pandora63]

October 24, 2002
Piston Deburring
Contributed by: Dr Drew http://www.hstuners.com (pictures available)

Boost is nothing but compressed air that is forced into the engine. Boost can increase engine HP - although, there are several drawbacks from boost (anytime a gas is compressed heat is a by product). This also works in reverse. When a gas is decompressed it reduces temperature. Such as Nitrous oxide. When it is decompressed to bar it is approximately -130 degrees.

Obviously compressed air has a considerably higher oxygen content than non compressed air. That extra oxygen allows for increased fuel to be added to the combustion chamber resulting in higher HP. Compression also has direct effect on HP that results from the power stroke. There are two different types of compression. Static compression and effective compression. Static compression is the division of the cylinder stroke volume by the combustion chamber volume. Effective compression is measured by taking bar ([14.7lbs/square inch]which is absolute atmospheric pressure)and dividing it by the how many pounds of boost the engine is under. Lets use 10lbs in our figure. 10 / 14.7 = 0.68 Add one; 0.68 + 1 = 1.68 Then multiply by the static compression. 1.68 X 10 = 16.80. As you can see the engine's compression ratio under boost is 68% higher than it's static at 10 lbs of boost. This is a very important fact to realize.

During the compression stroke of our engine the air and fuel mixture is compressed to 10 times it's size. Remember we learn earlier that when a gas is compressed heat is a by product. This is where the fuel's octane comes into play. Octane is a rating of how much the fuel can be compressed before it ignites itself via the heat from compression and combustion chamber temps. A fuel that is suited for a 10:1 static compression engine may not be suited for an engine that has a higher effective compression ratio. The more the mixture is compressed the more heat that is generated and in turn the higher octane fuel that is required. High cylinder temperatures have an effect on the compressed gases temperature. Cooler cylinder temps enable more compression or more boost to be had for a given octane fuel.

There are several different ways to keep cylinder temperatures lower. One is to remove all carbon deposits that are built up on the pistons and combustion chamber. Second is to remove all sharp edges in the combustion chamber and on piston tops. Third is to create a thermal heat barrier in the combustion chamber to prevent the cylinder from heating up. This can be done by ceramic coating all combustion chamber surfaces and piston tops. Sharp edges and deposits are the first to heat up. These can become so hot that they can ignite the air and fuel mixture upon introduction to the cylinder. Or they can increase gas temps during compression to beyond the fuels ignition point, then detonation or preignition occurs.

The deburring of the pistons can be done at home with some supplies from or your local hardware store. You want to pick up some 200 grit sand paper. The cloth stuff is the best to use because it is a lot more durable then the paper. Basically your goal is to smooth all the sharp edges and burrs from the piston. You want to try and not remove much material just to smooth over the edges without leaving any grooves. Then, after the rough edges are gone you want to take a piece of scotch bright and make the final finish. Smooth over all the surfaces on the pistons to ensure an even finish.

There are several different companies that coat pistons. There are also kits they sell to apply your own ceramic coating. You should try to steer clear of these for the reason of the coating not being durable. It is fairly inexpensive to have them coated. Here is a list of pricing. www.swaintech.com/price.html Here is a picture of the same piston after coating. (see picture at www.hstuners.com) This piston received the Gold coat dome finish and the PC-9 low friction coating on the skirts.

[Calesta]

More Swain Tech examples- these pistons have the TBC coating on top and the PC-9 low friction coat on the skirts. They were also deburred prior to coating.