Jake vs Exhaust Brake

4x4ord wrote:

Lynnmor wrote:
So what is this thing?

They want us to believe it is similar to a "big rig" engine brake. It is more effective than a standard exhaust brake but it is still nothing like a jake brake. If you think of an engine as an air pump you can imagine how restricting the exhaust raises the pressure at which the volume of air is being pumped at and creates more braking. Downshifting speeds the engine up which causes the engine to pump more air which also creates more braking. The Packbake holds the exhaust valve off its seat during engine braking. So with the Pac brake the piston pushes air past the slightly opened exhaust valve causing braking on the compression stroke. The pressure on the piston would be equal to the exhaust back pressure created by the restriction at the turbo. The cylinder would refill through the slightly opened exhaust valve on the power stroke and then offer the same braking as a typical exhaust brake on the exhaust stroke. Again it is the power require to force the air past the turbo that is creating the braking.

Sort of. When the valves stay closed during the compression stroke, much of the energy used to compress the air is returned to the crankshaft during the power stroke. Releasing that pressure through the exhaust on the compression stroke eliminates that.