BMW first introduced the M4 GTS three-years-ago, and it was the first to feature a Bosch water injection system. This boosted the standard M4’s horsepower from 443bhp to 493 bhp, thanks to the system. Simply put, the water injection system decreases the temperature before the combustion chamber in order to prevent the possibility of engine knocks or premature ignition by spraying distilled water onto the intake manifold, which comes from the 50-litre tank in the trunk. Since the air is denser and the temperatures lower, the automaker increased the turbocharger boost levels from 17.2 to 21.6 PSI, thus increasing horsepower. Read more for the explanation by Engineering Explained.
“Another advantage of the water injection system is that it could reduce thermal stress within the engine parts like the pistons, exhaust valves, and catalytic converters since they would be operating in lower temperatures. The turbocharger would also be subjected to less thermal stress. As the water injection system would only engage when driving in heavy load (5,000 rpm and wide open throttle), refilling the water tank in the trunk with water won’t really be an issue if it’s only a regular road drive,” said Yahoo News.