Can a heavy piston rob power?

[Shed tuner]

Inertia is a property of a stationary mass, Jon. A moving mass like a piston has momentum, and too light a piston reduces momentum.

picky picky.. I've misssed you Jim

Not quite. Splitting hairs, inertia is the tendency of an object to remain in the same state, either stationary or in uniform motion, resisting change.

You are my friend. Not like Jim