What is the normal cylinder pressure for a car engine?
2 Answers
Automobile engine cylinder pressure is around 1000kpa. Generally, gasoline engines are around 1000kpa, diesel engines are around 2000kpa, most fuel injection engines have cylinder pressures between 1200~1400kPa, and a few high-compression ratio engines have cylinder pressures above 1700kPa. A cylinder is a part of the car's combustion chamber where there is a piston pushed by the pressure or expansion force of the working fluid. The classification of cylinders is as follows: 1. Single-acting cylinder: Only one end has a piston rod, with air supplied from one side of the piston to generate pressure, which pushes the piston to extend, and returns via spring or self-weight. 2. Double-acting cylinder: Air is alternately supplied from both sides of the piston, outputting force in one or two directions. 3. Diaphragm cylinder: Uses a diaphragm instead of a piston, outputting force in only one direction, with spring reset. It has good sealing performance but a short stroke.
Cylinder pressure refers to the compression pressure within an engine's cylinders, which directly impacts the engine's power and efficiency. I pay special attention to it when driving older cars, as the normal range typically falls between 120 to 180 psi, or approximately 8 to 12 bar in more commonly used units. This mainly applies to gasoline engines; for diesel engines, cylinder pressure tends to be higher, usually above 20 bar. Accurate cylinder pressure measurements require the engine to be warmed up; otherwise, readings will be lower. If the cylinder pressure drops below 100 psi, the engine may experience difficulty starting, poor acceleration, and increased fuel consumption. Possible causes include leaking valves, worn piston rings, or aging cylinders. I once encountered this issue—my car made a coughing sound during startup, and after checking the cylinder pressure, one cylinder was found to be low. Repairing the valve seals fixed the problem. Maintaining proper cylinder pressure is crucial. Routine maintenance should include checking the compression ratio and performing simple tests with a compression gauge—differences within 10% are considered normal. Neglecting this could lead to costly major repairs, potentially costing thousands. So, don’t wait for problems to arise; proactive maintenance saves both hassle and money.
