The new BMW M4 GTS is almost hilariously expensive, nearly $100,000 more expensive than a base BMW M4. Part of the justification for the price comes down to a trick water injection system that blows from the car’s butt up its nose.

This new EVO video gives a full walkaround of the 493 horsepower car, but the interesting part focuses on the water injection system.

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Water injection has been pretty common in the hot rodding side of the car universe for ages. It came over from World War II fighter jets and works on a pretty simple idea.

Inject water into the intake, and as the water turns into a vapor. Much in the way that sweating works, that evaporation cools everything down. That gives you cooler combustion, and cooler combustion temperatures mean you can run lower octane fuels, higher compression, more boost, all without knocking. Cooler combustion means you can get an engine to make more power, basically.

We discussed this when the car came out, but I’d never seen elsewhere that the water reservoir is mounted in the trunk. You lift up the carpet and there’s your filler cap.

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I don’t know if this really works in justifying the car’s price tag, but it’s cool to see BMW now using hot rod tricks from back in the day on their fastest car ever.

Hey, if it works, it works.