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Methanol Injection

Car culture term

What is Methanol Injection?

A supplemental fuel system that sprays a fine mist of methanol or water-methanol mix into the intake charge, cooling the intake air and resisting knock on turbocharged engines running pump gas.

Methanol injection (also called water-methanol injection or meth injection) sprays a fine mist of methanol, water, or a water-methanol blend into the engine's intake stream, typically just before or after the throttle body. The evaporation of the methanol-water mix pulls heat out of the incoming charge air, reducing intake air temperature (IAT) significantly. Cooler, denser intake air is more resistant to detonation, allowing more aggressive ignition timing and boost pressure on pump gasoline than would otherwise be possible.

Methanol is also itself a fuel with a high octane rating (around 100+ on the RON scale) and high heat of vaporization. The methanol portion actually burns in the combustion process and contributes to power output, not just cooling. This makes meth injection a dual-purpose performance tool: charge cooler and supplemental fuel. The result on a turbocharged vehicle can be an additional 20-60 or more horsepower over what the same tune makes on pump gas alone, depending on the specific application.

Common meth injection systems include Snow Performance and AEM kits. They consist of a reservoir, pump, controller (often boost-triggered), and nozzle(s). Meth injection is popular on the Subaru EJ257, Mitsubishi 4G63, and boosted domestic V8 platforms. The key limitation is the requirement to keep the reservoir filled; an empty tank without failsafe tune reverts to the more aggressive timing without the charge cooling benefit, which risks detonation.

Related terms

TurboIntercoolerE85Flex Fuel TuningKnockOctaneECU tune

Frequently asked questions

Is meth injection safe for engines?
It can be, if the system is properly set up with failsafes. A properly tuned meth injection system with a failsafe (which pulls timing or cuts boost if the tank empties or the nozzle clogs) is relatively safe. Without failsafes, running an aggressive meth-dependent tune on an empty tank risks catastrophic detonation. Failsafes are non-negotiable.
Is methanol injection the same as running E85?
Related but different approaches. E85 is a primary fuel that replaces gasoline in the fuel system. Methanol injection is a supplemental spray added to a gasoline-fueled engine. E85 requires a flex-fuel tune and upgraded fuel injectors and pump. Meth injection works alongside the existing fuel system. E85 typically provides more consistent protection, but meth injection is a viable lower-cost approach for many builds.
How much does a meth injection kit cost?
A quality kit from Snow Performance or AEM costs $300-$600 for a basic single-nozzle setup. Additional nozzles, larger reservoirs, and more sophisticated controllers add cost. Installation is straightforward for someone with basic wrenching ability. The ongoing cost is the methanol fluid itself, which is relatively inexpensive.
Can meth injection replace an intercooler?
It can reduce intake air temperatures significantly, which is part of what an intercooler does. However, meth injection is supplemental; a quality intercooler is still beneficial. Some builds use meth injection to compensate for an undersized intercooler on a street car where packaging a larger intercooler is difficult.
What is the water-methanol mix ratio?
Common ratios are 50/50 water-methanol and 100 percent methanol. A 50/50 blend provides good charge cooling from the water and some fuel and octane benefit from the methanol. Pure methanol provides more octane contribution and cooling but less water-evaporation cooling. Pre-mixed solutions are available, or enthusiasts mix their own from ASTM D5797-grade methanol.
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