WesWorld

On a couple of rare US aircraft engines? I've found the Continental XI-1430 and the Lycoming O-1230, but little more than weight, displacement, and total horsepower. Bore size and piston throw would also be useful (for enlarged versions).

The Continental engine seems to have unrealized potential: it's small, light, and efficient, and for the current period puts out plenty of power. Long term it may not have enough displacement, being smaller than the Merlin, but it has potential.

The Lycoming has the same problem in spades: it's even smaller in displacement, it's flat (not so good for fighters, the Continental originally was a flat engine that was reworked into an inverted V for use in fighters), but it also is small, light and efficient. It was later coupled and used in the H-2470, but only in prototype aircraft.

The monstrous Lycoming R-7755 is also interesting, but mostly in the sense of "Good God, that's HUGE!" I don't know that it's a particularly useful engine, but it's BIG!

The Wright XR-2160 Tornado is also intriguing, but I can't seem to find much data on it.

XI-1430-1, Turbosupercharged liquid cooled inverted vee engine. 1350hp/3300rpm/s.l. 1600hp/3200rpm/25000ft on 100-oct fuel. 5.5" x 5.0" 1475lb weight. Questionable reliability

O-1230, horizontally opposed. Turbocharged and with fuel injection. 1200hp/3400rpm/s.l and 1200/3400/25000 on 100/130 fuel. 5.25" x 5.75". Weighs 1342lbs. Long development, reliability unknown

R-2160, liquid cooled radial. 2350/4150/s.l. 2350/4150/25000 on 100/130 oct.4.25" x 3.75". 2375lb weight. Extremely complicated

H-2470. Liquid cooled H engine with single stage two speed supercharger. 2300/3300/s.l. 2300/3300/1500. 2400lb

R-7755. Four row radial, turbosupercharged. 5000/2600/s.l. 5000/2600/10000 on 115/145 oct. 6.375" x 6.75" 6050lb

I have dimensions for most if needed.

Dimensions could be useful.

Yeah, reliability was an issue at least on the XI-1430, but then, when only 23 were historically built, it shouldn't be too much of a surprise. The one that Graham White has restored runs at 3700 rpm, which is a pretty good clip, and another test engine hit 2100 hp at 3400 rpm (but had 87.7" of boost).

Most can be found in this list.

That test engine seems pretty good for 2100/3400 but would need 115/145PN fuel and water injection to reach that level as its around (88" =) 28lb boost. Similar to the Merlin 100 series which is around 2080hp at 25lb (= 81") boost on British 150PN fuel (which is pretty much the same as 115/145). Test Merlins got rated up to 2300hp at 30lb (=91") boost without water injection and 2640hp at 35lb (=101") boost with water injection. There were some interesting tests post-war with 160PN fuel which managed up to 3300hp.

The only real option I feel is playing to the US's strengths, in large air cooled engines with turbochargers. The R-2600 isn't a bad engine now, its reliable and with reasonable power. The R-2800 is available in the early 40s at 1850hp, then 2000hp then 2100hp with special late versions getting up to 2800hp. The problem with these is that you need really large planes to be built around them, especially if you're going to incorporate a turbocharger. Its not really possible to get a turbocharged R-2800 into a smaller plane than the P-47.

The inlines all had problems, even the V-1710 which was the only one produced in real numbers. Single stage supercharging (and poor supercharger design) limited critical altitude compared to later Merlins. The turbocharged engine had good altitude performance but was massive and heavy. One way to go might be like the DB and Jumo series of engines, using water injection and nitrous oxide to compensate for the lack of power at altitude.

Which is not an unlikely way to go, given that in WW Germany and the US have a relatively long-standing relationship and NACA and the RLM have had an agreement on tech transfers for years. Technology has been flowing both ways already (Daimler-Benz has acquired some Allison manufacturing processes, Pratt & Whitney now has Junkers fuel-injection technology from the Jumo-208/P&W RD-1650 project, etc).

Who knows, maybe the Wright R-2160 Tornado will become the main-line engine for the future: yeah, it's complicated, but probably no more so than a sleeve-valve engine, and it's a nice diameter for a fighter.

Sleeve valves are less complicated than normal poppet valves apart from the valve gearing (which would be extremely complicated for a 42 cylinder radial). The part count is massively less. You've just got a crank which moves in parabolic motion moving and twisting the sleeve inside the cylinder.

With 42 cylinders it would be awful for maintenance. Changing 42 sparkplugs at once?