[serialk11r]

Yea I've thought of that too, but apparently BMW's newer cars have reduced engine braking, and some article I read said it was because it opened the throttle. I don't know how accurate this is though. It's possible that they deactivate the valves completely.

When opening the throttle all the way, most of the compression energy is returned to the piston but not all because exhaust valves open early (of course this is dependent on intake timing too). If the intake were completely plugged and no air were allowed to flow into the engine, the engine would expend energy expanding air at some equilibrium pressure in the manifold, and when the exhaust opens it would allow air to go into the cylinder, and then be pushed back out, not recovering energy. If a little bit of air were allowed to flow through, the energy lost at expansion decreases, but the energy lost to the throttle goes up. So I think it's hard to say...your cranking anecdote suggests it may be at some intermediate throttle opening.