Hello, I am new to this forum, And I had a question regarding Engine Braking I have been told that a lighter rotating assembly would produce better engine braking, if this is true could someone explain why? It would seem to me (But I do not know) that compression ratio would be more of a factor than weight of rotating assembly. Thank You

A heavier rotating assmebly possess more kinetic energy, that is, it acts like a heavy flywheel that takes more power/time to increase in speed but also take longer to reduce in speed. A lighter rotating mass will rev more quickly, decel more quickly because it reacts faster to internal friction and compression.