Rev limiter

They are intended to protect an engine by restricting its maximum rotational speed, measured in revolutions per minute (RPM).

Limiters usually work by shutting off a component necessary for the combustion processes to occur, whether it be fuel, air or spark.

In the case of "neutral" or shifting up too late, a rev limiter can easily keep engine RPM below the redline.

[2] Fuel-cutting rev limiters are the most common in road cars because they wear less on exhaust components, particularly the catalytic converter.

Ignition control rev limiting systems work by shutting off the spark plugs once the engine overspeeds.

[3] Vehicles equipped with drive-by-wire systems allow the ECU to modulate throttle position to keep engine RPMs in a safe range.

This is by far the safest method of limiting engine speed and is used on most modern production cars, as they don’t use a throttle cable.

In racing applications, extremely short hysteresis is desired so you won't lose all engine power suddenly if/when you hit the rev limiter.

If using a soft-cut rev limiter, the engine will start to cut fuel or retard ignition timing before the set RPM until it slowly reaches it and remains there.

At high engine speeds, the oil pressure rises to such an extent that the tappets 'pump up', causing valve float.

The first stage can be used to limit RPM levels when launching a vehicle from a stationary position, providing maximum power and traction.

[7] If an engine goes overspeed, commonly called "over-revving", damage to the piston and valvetrain may occur when a valve stays open longer than usual.