Grigg: Is a Jake brake the same as a vacuum release?
No. A Jacobs Engine Brake is a device that prematurely opens the exhaust valves near TDC on the compression stroke, dumping the compressed air - waisting energy, slowing the truck down.
Or this is how Jacobs describes it: "When activated, the Jacobs Engine Brake opens the exhaust valves near the top of the compression stroke, releasing the highly compressed air through the exhaust system. Little energy is returned to the piston, and as the cycle repeats, the energy of the truck’s forward motion is dissipated, and the truck to slow down." http://www.jakebrake.com/technology/engine.php
About noise: "FAQ9: I'm bothered by the noise of big trucks using their Engine Brakes, what can I do?
ANSWER: The federal government has required all vehicles manufactured since 1978 to meet noise requirements when delivered to the customer. Today, trucks are required to emit less than 80 dBa of noise when they drive by, as measured at 50 feet. So trucks have been required to meet noise requirements when they leave the dealership as new vehicles for quite some time. The real problem here is modified or defective exhaust systems. There is a good chance that the trucks that are causing the disturbance are running with straight stacks or gutted mufflers. Some are poorly maintained vehicles; some drivers simply enjoy making noise. In any case the use of the engine brake is not the problem."
