Direct port water methanol injection setups have gained popularity in recent years, and it’s easy to see why as the array of feed lines and injection nozzles turn an intake manifold into a work of art that screams power! This system of providing a water methanol nozzle for each intake runner is gaining traction in a serious way so we decided to discuss the science behind it and look at the results compared to single point injection.

Aesthetics aside, the direct port system has been touted as a superior way to inject water methanol because it will ensure that each cylinder receives the exact same amount of spray and therefore no cylinder can be starved. This is felt to provide more precision and has been somewhat driven by the evolution of gasoline engines as they have moved from throttle body injection , to sequential multi-port fuel injection and now to direct injection. It has been made a bit of a universal truth that if car manufacturers have found injecting closer to the cylinder is better there is no reason not to follow their lead.

The popularity of direct port injection for water methanol systems has also been driven by carbureted engines when a poor manifold design could lead to cylinders being starved and consequently damaged by running lean. These stories have stuck around even after sequential fuel injection has ensured every cylinder receives the same amount of fuel. It’s easy to see why the direct port injection systems have become the perceived pinnacle of water methanol injection when we take these accounts at face value.

We want to take a more in depth look at the science behind these widely held beliefs and look at the real-world comparison of a single point injection system and a direct port injection system. For the purposes of this article a single point injection system will be defined as one or two nozzles mounted in either a throttle body spacer plate or the intake tube/charge pipe.

A single point injection system sprays a mist into a uniform volume of air as it moves through a charge pipe of the throttle body. The air speed and heat carries the vapor along with it as the manifold directs the incoming air to each cylinder. The argument is that this method cannot ensure the same amount of vapor reaches each cylinder because the closest cylinders or those with the shortest runners will get the most vapor. Aside from modern intake manifolds being very well designed to ensure that every cylinder gets comparable air volume and velocity, this theory does not take into account intake valves opening at different times.

The theory that the water methanol vapor will follow the path of least resistance and over feeds the nearest cylinders assumes the intake valves are always open drawing a constant stream of air. In a 4 stroke engine, the intake valves are potentially open only about 25% of the time; therefore, the air demand is a variable condition inside a manifold. The best way to think of the conditions in a forced induction manifold is that rather than a river following the easiest path we have a compressor tank with a row of valves being opened at different times. The air volume and accompanied vapor is waiting in the intake runners at the same pressure waiting for the intake valve to open. So the Intake manifold on a forced induction vehicle acts as a kind of reservoir holding the pressurized air charge until each cylinder is ready for it.

This describes a forced induction manifold operation where the incoming air charge is pressurized and forced against the intake valves, which accounts for the vast majority of vehicles operating with a water methanol system. With it being proven that the vapor will be evenly distributed among each cylinder from a single-point injection system we can look at the power aspect of the argument; Does a direct port setup allow the water methanol system to make more power?

The power to be gained from water methanol injection systems depends entirely on the level of heat and octane deficiency they have to treat. Water and methanol are added to the incoming air charge until the cylinder environment is optimized to be able to run ideal timing and fuel maps. Because we have shown that regardless of the injection point all cylinders are receiving an equal share of the vapor, the power to be gained relies entirely on the ability to inject the appropriate amount of fluid at the appropriate time to provide the necessary benefits.

Most gasoline engines up to approximately 1,000 RWHP will receive ample injection from only 2 large nozzles mounted in a common air area for the engine. Too much flow will actually bog an engine down and cost power because the cylinder does not have the heat to create a clean burn. This is an important consideration when deciding if a direct port injection system is right for you because as the number of nozzles increases, the amount of fluid injected will climb.

For instance, on a V8 engine with 8 of our smallest nozzles (#1 60ML/MIN), that engine will need to be making about 850+ forced induction horse power to make efficient use of the fluid. This is even more important in smaller 4-cylinder engines where the engine should be making at least 400+ HP and over 23 pounds of boost to make use of the smallest nozzles. These levels of power are generally attainable but we do want to stress that lightly modified engines should be very cautious going to this setup as most customers will lose HP due to over injection.