Quote:
Originally Posted by strat61caster
Actually the valves open and close as if the engine is still being operated, due to the camshafts still being directly attached to the crankshaft so it's the compression stroke of the motor slowing the vehicle down as there is very little resistance from the intake stroke (comparatively).
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Most of that energy is recovered on the expansion stroke though - the air in each cylinder is basically acting as an air spring during the compression and expansion strokes when the engine is running this way. I would guess you actually do get a significant portion from the drag from the vacuum generated during the intake stroke. As for the valves opening - yes, they do operate normally. However, the throttle itself is closed, so a pretty significant vacuum is generated in the intake manifold as the engine pumps air from the intake to the exhaust side of the engine.