What is the expected compression range during a dynamic compression test at idle?

During a dynamic compression test at idle, the expected compression range is between 60 to 90 psi. This range is indicative of a healthy engine that is functioning correctly under operating conditions.

At idle, the engine is running at low RPMs, and the valves are in their closed positions during the compression stroke, allowing for an effective build-up of pressure in the cylinders. A reading within this range suggests that the engine is sealing properly, with adequate cylinder pressure necessary for efficient combustion.

If the compression readings fall below this expected range, it may indicate issues such as poor sealing of the valves, worn piston rings, or head gasket failure. Conversely, significantly higher readings might occur in high-performance or racing engines, which are designed to operate under different pressure and performance requirements.

Understanding the expected compression values helps technicians diagnose engine health; ensuring readings fall in the proper range supports optimal engine performance and longevity.