Basic theory about engine compression

In this article we will try to explain the basic foundations on compression in 4 -stroke engines. We have always heard that more compression in the same engine, let's verify that there is true in this statement.

What is compression
The Compression or Compression Rat (CR) index is a measure that is obtained from dividing the volume that exists in the combustion chamber (and cylinder) with the piston in the lower dead point (BDC) by the volume that exists in this camera with The piston in the upper dead point (TDC). That is, it is the relationship of the air that is compressed every time the piston rises.

For example, if with the piston below (BDC) we have a volume of 10cc and when the piston (TDC) we have 1cc volume in the camera then we can say that the air has compressed in a 10: 1 ratio, this would therefore be The CR of our engine.
Only as a curiosity in this article we refer specifically to “mechanical compression”. There are also other types of compression measurements (corrected, static, effective, starting, dynamics ...). Different camshaft also greatly influence the compression ratio.

Advantages and disadvantages of compression increase
The internal combustion engine is an air pump. We try to introduce as many as possible, and then compress it and finally “burn it” with the help of a little gasoline, the rapid expansion of combustion will cause a downward force in the piston responsible for the crankshaft movement, and directly related to the power of the engine.
For the same amount of air, the more compressed in the combustion chamber the more energy will release after the explosion, and at the same time the highest initial compression will favor the ignition of the air/gasoline mixture, all causing a more efficient combustion.
In exchange for this, greater mechanical stress will be created in the moving parts and the operating temperature will rise, so we always have to look for the ideal balance between the increase in the compression index (CR) and the useful life of the engine components .

Compress your engine
It must be said that generally the original motors of the “Cruiser” motorcycles come quite reduced from compression, as they have to function well in all types of markets (the quality of gasoline can differ between several countries) and under all kinds of conditions.
If we have access to quality fuel such as 98 octane or higher or we use Octaneing potentiators We can increase the efficiency of our engine slightly raising compression.

Because mechanical slacks will be reduced, the engine should not be forced under these conditions, letting it warm before aggressively accelerating, in this way the metal of the components will have expanded enough to maintain the recommended values ​​and avoid mechanical failures.
It is also important to know that the increase in compression should be performed on a completely “healthy” engine, it is no use to correct a defect or power failure by increasing compression, the initial problem must first be solved.

Different ways to get the same result
There are several ways to increase the compression of a standard engine, we will list some of the most used.

• Fine Cynt Boards: There are manufacturers that develop special butt joints that reduce combustion chamber, increasing internal pressure.

• Mechanize the cylinder or the butt: some thousandths are reduced some of these components, achieving a smaller combustion chamber. Only for experts.

• SPECIAL CODATES: There are manufacturers that offer butt with combustion cameras designed to optimize combustion and increase compression.

• Big Bore Kits: When we install larger cylinders and pistons we are increasing compression, since for the same combustion chamber we have more air initially. They are preferred since apart from the improvements due to compression increase there is nothing better than an increase in displacement when obtaining more torque and power.

• Higher pistons: various manufacturers offer pistons with the highest crown, resulting in a compression of the major mixture during the TDC.

The assembly is only the beginning

Once we have selected the way to increase compression and after assembling the components, the “tuning” process is pending. Having changed the internal operating conditions of the air related to the air and fuel it is necessary to readjust the ignition and carburation or injection correctly.
When we have finished this step we will find a more "happy" engine, which will accelerate brilliantly and will also be more efficient.

Frank Burguera

#mecanicaharley