Are there any real-world equivalents to spitting fuel into the engine?

This question is likely better asked over on https://mechanics.stackexchange.com/

My non-mechanic understanding is that, first of all, most of the vehicle accouterments in Mad Max are mainly there for show rather than practical purposes.

That said, what the warboys are spitting into are the air intake valves. This is what feeds the engine its combustion oxygen. When they show above the hood, they are often air ram intakes and/or part of a supercharger.

The more oxygen the engine can 'eat' the more fuel it can also 'eat' and therefore increase output. My guess is that the spitting of fuel into the intake is to replicate adding fuel via fuel injection. It's obviously more dramatic to do it manually while riding on the hood in the middle of the desert.

In addition, my guess was that it wasn't necessarily gasoline they were spitting in but perhaps pure alcohol.

Note that I am no mechanic, and I do not recall specifically the lead-up to that scene in the film, but I do know that there is such a thing as "water injection" which is really methanol+water injection (or humorously "meth injection").

I think the idea is that the methanol is higher octane (or rather increases the fuel octane, slowing detonation) and the water plays some role in cooling the fuel-air mixture enough to prevent premature detonation, which leads to some minor efficiency boost.

I think that these systems are banned in racing sometimes, probably because if they fail to cool things down properly, and the engine is tuned up to work tightly with them (for racing/max performance), then you get what some folks describe as an "engine grenade."

Presumably the vehicles are (at least fictionally) using the hood scoop to grab cool air and funnel it into the carburetor, and so they are doing the equivalent of wiping the sweat off the brow of the surgeon in a melodrama.

Beyond that, I don't know if the specifics of what they are doing adds up (there are several places in the engine chain to inject the water), nor do I think they tell us what the fluid is. 160-proof Methanol or ethenol would still be distasteful, but probably more pallatable than gasoline.

further reading here (4. Pre Throttle Body/Carburetor Injection) and here