From the experimental research geek-out department:

“The experimental subtasks involved quantifying the reduction in engine friction for a
prototype rotating liner engine relative to a comparable baseline engine. Both engine were
single cylinder conversions of nominally identical production four-cylinder engines. Hot
motoring tests were conducted initially and revealed that liner rotation decreased engine
friction by 20% under motoring conditions. A well-established model was used to estimate
that liner rotation should decrease the friction of a four-cylinder engine by 40% under hot
motoring conditions. Hot motoring tear-down tests revealed that the crankshaft and valve
train frictional losses were essentially the same for the two engines, as expected. However,
the rotating liner engine had much lower (>70%) piston assembly friction compared to the
conventional engine.”

From “Reduced Engine Friction and Wear” (PDF), a DoE-funded experimental study performed at the University of Texas by mechanical engineering professor Ron Matthews.