The LRFIX Compression Ratio Calculator calculates the ratio of an engine's cylinder volume at bottom dead center to top dead center.

Compression Ratio Calculator

What is a Compression Ratio Calculator?

A Compression Ratio Calculator is a tool specifically designed for small engines to determine the engine's compression ratio. This ratio is a key factor in engine performance and efficiency.

By using this calculator, you can easily compute the compression ratio of your engine based on several important parameters.

Tip: For a complete understanding of your engine’s performance, use an Engine Displacement Calculator to determine the engine's total volume first.

Then, use this Compression Ratio Calculator to assess how the compression affects your engine’s efficiency and power.

Why is Compression Ratio Important?

  1. Engine Performance: The compression ratio affects how well an engine converts fuel into power. A higher compression ratio can lead to increased engine performance and power output.
  2. Fuel Efficiency: Engines with higher compression ratios generally burn fuel more efficiently, which can improve fuel economy.
  3. Engine Knock: Higher compression ratios can lead to engine knock (pre-detonation). Understanding the compression ratio helps you select the appropriate fuel and avoid engine damage.

How to Use the Compression Ratio Calculator

  1. Bore Diameter (inches): Enter the diameter of the engine’s cylinder bore. This is the width of the cylinder where the piston moves.
  2. Stroke Length (inches): Enter the length of the piston’s movement within the cylinder.
  3. Deck Height (inches): Enter the distance from the top of the piston at its highest point to the cylinder head.
  4. Cylinder Head Volume (cubic inches): Enter the volume of the space above the piston when it is at its topmost position.

Example Calculation

Suppose you have the following engine specifications:

  • Bore Diameter: 3.5 inches
  • Stroke Length: 4 inches
  • Deck Height: 0.1 inches
  • Cylinder Head Volume: 20 cubic inches

Using these values in the calculator will yield the compression ratio, which tells you how much the air-fuel mixture is compressed within the engine’s cylinder.

How to Interpret the Result

The calculator will display the compression ratio as a number (e.g., 9.5:1). This ratio indicates how much the air-fuel mixture is compressed relative to its original volume.

A higher ratio means greater compression, which can lead to better performance and efficiency but may require higher-octane fuel to avoid knocking.