What is a blower or pump that forces air into cylinders at higher than atmospheric pressure called?

The term for a blower or pump that forces air into cylinders at higher than atmospheric pressure is a supercharger. Superchargers work by compressing the intake air, allowing more air (and consequently more fuel) to enter the engine's cylinders. This increased air density can lead to improved engine performance and power output.

Superchargers are typically mechanically driven, often by the engine's crankshaft, which allows them to provide immediate power boost as soon as the engine starts to rev up. This characteristic differentiates them from other devices that may serve a similar function but operate in different ways.

While turbochargers also enhance engine power by forcing more air into the cylinders, they do so by using exhaust gases to spin a turbine, which may introduce a delay in power delivery (known as turbo lag). Compressors can refer to various types of devices that compress air, but the context here specifically pertains to the function of increasing the intake air pressure directly affecting engine operation. Fans are primarily used for cooling and airflow rather than boosting engine performance.