brake and mostly found on older trucks. It has a limited effect, and more advanced systems as described below are near universal on newer heavy vehicles. Compression release brake A compression release brake (also known as a Jacobs brake or "jake brake"), is the type of brake most commonly confused with real engine braking; it is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, so the large amount of energy stored in that compressed air is not returned to the crankshaft, but is released into the atmosphere. Normally, during the compression stroke, energy is used as the upward-traveling piston compresses air in the cylinder; the compressed air then acts as a compressed spring and pushes the piston back down. However, with the jake brake in operation, the compressed air is suddenly released just before the piston begins its downward travel. (This sudden release of compressed air creates audible sound waves similar to the expanding gases escaping from the muzzle of a firearm.) Having lost the energy stored within the compressed air, there is no "spring back" so the engine must expend yet more energy pulling the piston back down again. This type of brake is banned or restricted in many residential locations because (unless properly muffled) it creates a jackhammer or machine gun-like sound loud enough to disturb the peace, including waking people at night. It is very effective, however, and creates immense amounts of braking force which significantly extends friction brake life – a diesel engine can produce up to of braking power at 2,100 RPM. Exhaust brake An exhaust brake works by causing a restriction in the exhaust, much like the intake throttle causes in a gasoline engine. In simple terms, it works by increasing the back-pressure of the exhaust. Nearly all of these brakes are butterfly valves similar to a throttle valve, mounted downstream of the turbocharger if there is one. Exhaust obstructions Modern diesels are subject to many strict controls on emissions and often have many obstructions in the exhaust, which cause them to feel like they have some engine braking like a gasoline engine. The main ones are: Turbocharger creates some back-pressure when it is stalled Exhaust gas recirculator (EGR) valve redirects exhaust gas back into the engine intake, often through a restricted/narrow pipe. Diesel particulate filter (DPF) is designed to capture soot