[Christ]

I thought the engine (jake) brake kept the exhaust valves closed longer so that the engine had to compress the air twice (bleeding off energy), but only partially the second time before it was let out of the engine in a high-pressure blast through the exhaust valve...

At least that's how I understood it... right or wrong?

EDIT: OK, I just ed-jama-cated muhself. Apparently, it opens the exhaust valve at the top of compression to keep the compressed air from acting like a spring and forcing the crankshaft back down, so the energy bleed happens just from the initial compression of the air intake in the first place.

Thanks for that!