How to Calculate Engine Compression Ratio

When your engine begins to run poorly, you need to measure the engine compression ratio. The engine compression ratio measures the air/fuel mixture, as it is confined and pressed into a smaller volume in the engine’s cylinder. The molecules are placed under high pressure. In short, it will tell you which cylinders are not working properly. Bad cylinders can lead to major engine problems.

Tools and Materials

  • Electronic Engine Analyzer
  • Owner’s manual

Step 1 – Engine Compression Ratio

The most common engine compression ratio is 140 to 160 pounds per square inch. This number can differ a little. The engine size will have a specific engine compression ratio. Consult your owner’s manual for the correct ratio.

Step 2 – Start Engine

You need to start your engine before you can measure the ratio. The cylinders and pistons need to running.

Step 3 – Electronic Engine Analyzer

Connect the electronic engine analyzer to a cylinder. The engine compression ratio will be measured. Continue through all of the cylinders, to collect each ratio. Look at the data to see which cylinders were working the hardest. These cylinders are not bad. It is the cylinders with the lowest engine compression ratio, that were working the least, that you want to focus on.