... so that other countries making the engines in the 1930s-40s don't feel neglected. So the French make HS 16Y instead of the 18Y, RR makes the Merlin-based H16 (or even the Buzzard-Griffon-based H16), Allison makes a V-1710-based H16, Chrysler makes a H-2200 instead of IV-2200, Napier makes one big & powerful H16 instead of Sabre etc.
Cancel the other types that are getting in the way in the respective companies. There is no requirement for sleeve valves to be incorporated.
Shortening of the stroke is allowed, so that engines are less bulky, and the RPM can go up. Motor-cannon installation where wanted/desired/required. Engines for fighters and bombers alike. USAAC/AAF will probably want to support the engine with a turbo. 2-stage superchargers by mid war, at least by the companies that were making these by early/mid-war.
Engine halves can operate independently if wanted.
Cancel the other types that are getting in the way in the respective companies. There is no requirement for sleeve valves to be incorporated.
Shortening of the stroke is allowed, so that engines are less bulky, and the RPM can go up. Motor-cannon installation where wanted/desired/required. Engines for fighters and bombers alike. USAAC/AAF will probably want to support the engine with a turbo. 2-stage superchargers by mid war, at least by the companies that were making these by early/mid-war.
Engine halves can operate independently if wanted.