During WW2 the airplanes had up to 115 octane and they still used water injection and as far as I know the unlimited airplane racers still use it ''ADI'' anti detonation injection. Notice how much Ricardo leaned the engine.
In ''The 1000 BHP GRAND PRIX CARS '' this is the first paragraph ''Rocket fuel' made it possible.The ball started rolling in mid 83 when BMW countered Renault's use of water injection by fuel technology.Injecting water into a turbocharger engine's 'charge air' did more than merely assist cooling; for reasons that had no formal, text book explanation the acted as a combustion stimulant, increasing power. Pre war turbocharged aircraft engines had used water injection injection to extend payload. Having picked up on the idea, Renault and Ferrari denied that water cinstituted a power boosting additive: there was no technical explanation to prove otherwise. BMW on the other hand saw more could be gained through manipulation of the composition of the fuel itself.''
JL222