The premise behind water injection is simple: Squirt a mixture of water and methanol–windshield washer fluid, basically–into the engine’s combustion chamber to cool the intake charge and prevent detonation.
A few factors decide a given fuel’s detonation point: intake air temperature, ignition timing and cylinder pressure combination. Cylinder pressure can be developed by compression ratio, supercharging or turbocharging. If you can reduce one of the three variables, then you can increase one or both of the other two.
The water/methanol mixture vaporizes and cools the intake charge significantly, allowing you to increase the timing and boost. In layman’s terms, water injection can produce the same effects as high-octane race fuel–but without the cost or complexity of finding it at the pump.
This technique has been around for decades, but it has only become a mainstream modification in the past few years. Credit more precise engine control systems with making water/methanol injection durable enough for everyday use. Additionally, companies like AEM now offer turnkey, all-inclusive kits.
Okay, so water/methanol injection is relatively easy to add. But is it really necessary? Here’s a handy guide to making that decision.
Step 1: Does your engine have a high compression ratio? Or is it fed by a turbocharger or supercharger?
If your answer is “none of the above,” then water/methanol injection probably isn’t a wise investment. If you do have one or more of these things, move on to Step 2.
Step 2: Can you adjust your ignition timing and/or boost pressure?
Installing water/methanol injection without retuning your engine will usually cost horsepower, as the water replaces some of the combustable air inside the engine. If you can’t advance the timing, increase the boost pressure, or both, don’t bother adding water/methanol injection. If you can, move on to Step 3.
Step 3: Are you willing to void your warranty?
Manufacturers aren’t too fond of extra water inside their engines. And their caution isn’t unfounded: If the water/methanol injection tank runs dry–you may need to fill it up at every gas stop–then detonation and engine damage are likely. If there’s a malfunction, the engine could hydrolock. Basically, if you still go to your dealer for oil changes, water injection isn’t for you. If you’re just cautious, we suggest adding a failsafe mechanism to your system. AEM offers them with its kits.
Practical Exercise
Wayne Presley at Very Cool Parts has made more than a few trips to the dyno. He recently used a water/methanol injection system while tuning a Dodge SRT-4.
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We had a 2005 Dodge Neon SRT-4 in the shop for a fresh engine with forged rods, forged pistons, cams and ARP head bolts. It was being fed through an AGP 50 trim turbo with an AGP front-mounted race intercooler.
After breaking in the motor, the tuning process on the dyno began with good results. The motor was pulling well through 18 psi of boost using 93-octane pump gas with no detonation.
When I turned up the boost to 20 psi, the knock sensor started pulling timing to protect the motor, causing a drop in power that’s easy to see in the graph below. At the wheels, we were seeing 341 horsepower and 370 ft.-lbs. of torque. We expected more.
We had already added the largest intercooler that would fit in the front of the car, but we needed to cool the manifold air temperature more. So,I added a water/methanol injection system. This was a system that progressively added more mix in relation to the boost level. I set the start point to 12 psi and ramped up to maximum flow at 18 psi.
Thanks to the cooler intake charge, I was able to add ignition timing as well as increase the boost to 22 psi. The horsepower and torque climbed up to 395 and 401 respectively. That’s 54 more wheel horsepower with zero detonation, all while using the same 93-octane fuel. The only equipment change was the addition of the water/methanol injection.
I highly recommend a system featuring a warning indicator or other failsafe to let you know if the system stops working for any reason. And use either the premixed water/methanol solutions or mix your own with distilled water. The orifices in the spray nozzle are very small, and tap water will have minerals in it. This will eventually clog the nozzle just like the hard water does to your shower head at home. When that happens, little or no mix is injected, and that extra boost and timing you’ve added to the tune might lead to some very bad and expensive noises.–Wayne Presley
