||This article has multiple issues. Please help improve it or
discuss these issues on the talk page. The term is often
confused with several other types of braking, most notably
compression-release braking or "jake braking" which uses a
different mechanism entirely. Correct use of the term only
applies to petrol engines and other engines that throttle air
intake (As opposed to, e.g. diesel engines or electric engines).
Petrol (gasoline) engines  The term engine braking usually
refers to the braking effect caused by the closed-throttle
partial-vacuum in petrol (gasoline) engines when the accelerator
pedal is released. While some of the braking force is due to
friction in the drive train, this is negligible compared to the
effect from the vacuum. When the throttle is closed, the air
flow to the intake manifold is greatly restricted. The concept
can be illustrated by the amount of effort required to blow/suck
through a thin tube vs. a thicker one. It is the work the engine
has to do against this restricted air f