Limiters prevent damage to an engine by interrupting the power that is distributed to the spark plugs, this prevents the engine from operating above a pre-determined RPM level known as the redline. The RPM level that results with the spark being arrested can be a constant level, or, with the proper ignition control modules, variable. Variable rate ignition modules can be adjusted quickly and easily to achieve the appropriate RPM limit for different situations, such as street racing, drag racing, road course racing, highway driving, and lawn turfing.
Multiple stage ignition modules offer greater RPM limit control. The first stage can be used to limit RPM levels when launching a vehicle from a stationary position, providing maximum power and traction. The second stage is activated after launch to set a higher RPM limit for wide-open-throttle acceleration.
Engines with hydraulic tappets (such as the Buick/Rover V8) often have what is in effect a rev limiter by virtue of their design. The tappet clearances are maintained by the flow of the engine's lubricating oil. At high engine speeds, the oil pressure rises to such an extent that the tappets 'pump up', closing the valve clearance and preventing the valves fully closing. This sharply reduces engine power, causing speed to drop.
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