If a WWII fighter engine were produced with today's technology, what would we get?
It's easy to forget that the technology that produced the great aero-engines of WWII is seventy years in the past. On a power to capacity ratio the motorcycle in my carport makes a Rolls Royce Griffin look puny. So, forget the jet engine ever happened- if we designed an engine of the same dimensions as those used in the Spitfire, 109 or Thunderbolt with today's technology, how much power could we get? What would be the limiting factors? Where the hell is Lord Lucan? Answer these questions and eternal fame will be yours.
My suggestion would be that the engines would have oversquare dimensions, and use a larger number of smaller cylinders.
The Rolls-Royce Griffon was a 36.7l (6" bore x 6.6" stroke. 2239ci) V-12. Its ultimate versions produced around 2500hp at 2750rpm with +25psi boost.
In 1945 a Rolls-Royce engineer, Stewart Tresilian, proposed an alternative 2500hp engine. It would be an X-16 with bore of 3.9" and of stroke of 3.3", for a capcity of 10.3l (630ci). The engine would be supplied by the Griffon supercharger. The max rpm would be 7250. The length was less than half the Griffon's, so less than 40" (1016mm) in length. The engine would be about the diameter of the supercharger housing. This means a maximum of about 30" (762mm), probably a few inches less. For comaprison the Griffon was 30.3" wide x 46" tall.
I would think that a modern piston aero engine would go along similar lines, with improvements in stressing ana materials the weight would be reduced and the engine made more compact. Modern ignition and fuel systems would raise the engine's efficiency and power, as would modern compressor technology.
I know that there are 630ci V8s that can make 2500hp, but under the aero engine type tests of WW2 they certainly wouldn't get rated that highly. The British test, for example, lasted for 114 hours. The US test required that an engine run for 7.5 hours at maximum power (war emergency power) in 5 minute bursts for it to rated at that power level.