An apparatus can include: a piston head configured to be disposed inside of a cylinder of an engine; a connecting rod device coupled to the piston head and extending therefrom, the connecting rod device including: a variable-length connecting rod including a female component with a hollow body and a male component disposed at least partially inside of the female component, the female component configured to be coupled to a crankshaft of the engine, one or more rollers rotatably disposed in or on the male component, and a connecting rod magnet movably coupled to the male component proximate to a position of the one or more rollers; and a piston coupling mechanism disposed at least partially inside of the piston head to couple the connecting rod device to the piston head. The connecting rod device can be configured to transition between a locked state and an unlocked state.