In a perfect world we’d be able to adjust spark advance and turbo/supercharger boost to get the cylinder pressure that makes the most horsepower. Unfortunately, in the real world, high temperature and pump gas octane limitations conspire to limit timing and boost pressure, and if these limitations are exceeded, it can result in harmful, engine damaging, detonation. Water/methanol injection reduces air intake temperature and boosts octane, allowing timing and boost to be increased for optimal performance of your vehicle .
Water/methanol injection is also beneficial for diesel engines. Excessive Exhaust Gas Temperatures (EGTs), which can occur when towing heavy loads and up steep grades, can cause serious engine and turbocharger damage. Water/methanol injection cools the intake air charge, reducing combustion temperature and EGT. And when the water vaporizes, the additional oxygen allows the diesel fuel to burn more completely, for more efficient combustion, and burning the methanol creates more power.
Water/methanol injection was first used during World War II on supercharged and turbocharged fighter planes. A typical modern system includes a fluid tank, pump, injector nozzle, and a controller to regulate water/methanol delivery. A highly atomized mist of the fluid is injected into the intake air stream, where it vaporizes, absorbing heat and cooling the air charge. The cooler, denser charge provides more oxygen so more fuel can be burned, and slows the rate of combustion, preventing detonation and allowing more boost and timing advance to be used for more power. The methanol also cools and controls combustion, and as a high octane fuel itself, it effectively raises your fuel’s overall octane rating.
Water/methanol injection can definitely benefit performance engine tuners because it will allow them to safely dial in more timing and boost. But these systems can also help late model factory stock turbo gas engines because the ECM will detect the cooler intake air temperature and automatically advance timing, which improves combustion efficiency, increasing power and fuel economy. In addition, as the water/methanol vaporizes and expands, a steam engine effect is created which provides additional downforce on the pistons and also removes carbon from the combustion chamber, which if allowed to build up could create hot spots that could cause detonation.