What happens when revving the engine in neutral?

[McMiguel]

Revving the engine in neutral subjects the moving parts of the engine to significant inertial forces, affecting its reliability and lifespan. Below are the impacts of revving the engine in neutral: Exceeding normal operational stress: When the car is in neutral, the engine has no power output. Revving the throttle causes the engine speed to rise sharply, forcing rapid acceleration of moving components such as pistons and connecting rods. This generates substantial acceleration, subjecting them to high alternating loads. The stress on pistons, piston pins, connecting rods, connecting rod bolts, and crankshafts will exceed normal operating levels. Component combustion: The sudden increase in RPM during revving can cause lubrication to fail to keep up with the friction pairs, easily leading to issues like cylinder scoring and bearing seizure. Prolonged revving in neutral can result in severe incomplete combustion. If unburned fuel-air mixture ignites outside the cylinder, it may cause vehicle self-ignition. Incomplete combustion also promotes carbon buildup, potentially clogging the catalytic converter and causing abnormal high temperatures. These extreme temperatures may lead to electrical wiring fires, with serious consequences.