During the compression stroke, the fuel/air mixture is compressed, and due to thermodynamic laws, the compressed mixture increases in temperature and pressure. How does an increased compression ratio affect engine performance? To understand how increasing the compression ratio affects performance, we have to start with understanding what happens to the fuel/air mixture on the compression stroke. Swept volume is the volume displaced as the piston moves through the stroke, and clearance volume is the volume of the combustion chamber with the piston at top dead center. Want more technical details on making compression ratio calculations? Read this. Reductions in clearance volume are typically achieved by modifying the geometry of the piston crown so that it occupies more combustion chamber space. When alterations to the compression ratio are made, the clearance volume is reduced, resulting in a higher ratio. There are multiple calculations to finding clearance volume, but to keep this introductory, we are sticking to an overview. The clearance volume is the volume of the combustion chamber when the piston is at top dead center (TDC). The swept volume is the volume that the piston displaces as it moves through its stroke. Shown below is the mathematical equation that defines compression ratio: The compression ratio compares the volume above the piston at bottom dead center (BDC) to the volume above the piston at top dead center (TDC). Let’s start with a quick review of what the compression ratio is, then we’ll get into how it affects performance. It’s important to first understand what effects high-compression has, the anatomy of a high-comp piston, and what applications typically benefit most. Bumping up the compression in your motor should be an informed decision. To better understand, we’ll take a look at what increasing compression ratio does, what effects this has on the engine, detail how high compression pistons are made, and provide a high-level overview of which applications may benefit from utilizing a high compression piston.

Piston manufacturers like JE Pistons offer high compression piston options for many applications, but there are important merits and drawbacks you should consider when deciding if a high compression piston is right for your application.

Whether you are racing or looking for increased performance out on the trail, there are a plethora of performance upgrades to consider to increase the power of your machine. We take a look what effects higher compression has, designing high-compression pistons, and what factors to address when considering adding one. High-compression pistons are a common upgrade for dirt bikes and other motorcycles, but bumping compression isn’t always beneficial.

Combustion Chamber Mold Making Instructions.Ring Installation Guide 4032 Pistons Instructions.

High compression engine