Is It Harmful to Rev the Engine in Neutral for a Manual Transmission Car?

[Malcolm]

Whether revving the engine in neutral is harmful to a manual transmission car depends on the following situations: If it's just a short-term rev in neutral: An occasional occurrence, even if the engine speed momentarily reaches 4000 or 5000 RPM, will have minimal impact on the car and can be considered negligible, causing no harm. If the engine is revved for an extended period: This can be damaging to the car. When the car is in neutral, the engine has no power output. Revving the throttle in this state causes the engine speed to rise sharply, forcing rapid acceleration of moving parts such as pistons and connecting rods. This generates significant acceleration forces, subjecting these components to high alternating loads. The forces on the piston, piston pin, connecting rod, connecting rod bolts, and crankshaft will exceed those under normal operating conditions, potentially compromising the engine's reliability and lifespan.