Reading a book on development of the Douglas DC3. The TWA performance spec called for the ship to break ground within 1000 feet at max all up weight. Didden quite make it. Engineers on the Wright Cyclone engines noted that the cases were full of oil at full power and added drain holes. That added 20HP, they then went further and put scrapers in the case to wipe oil off the crank and rod assembly (radial engine) and saw another 63HP. Thats 83HP or in the case of the Wright, 10% power increase just by keeping oil off the rotating assembly.
Nothing new under the sun......................

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Remember, tracer works both ways.

Oils a drag, they say your engine picks up 20 hp if it loses oil pressure

One of the guys in Cam County dropped a full 10th going from 20-50 mineral oil to a synthetic 5-30 or something similar. The lighter weight oil was all he changed and ET's dropped consistently.

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"Engines are like cheese, big blocks are better value"
(Quote from the dustup by Rod Wills, R3DN3K Rodshop Waihi)

In this case it seems the drag was the ball of oil around the crank and rod assy. Them ole radials only have one rod bearing and it its a roller usually, and one ball race and one roller for the mains. 80W single weight ashless oil like treacle and they burn/leak about 3USGal an hour, the old sweeties.

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Remember, tracer works both ways.