Duramax Water-injection Install

Updated Mar 27, 2015


We give Big Red’s 6.6L Duramax a shot of cool fuel with an AEM water-injection system; 50-state-legal kit lowers EGTs under heavy loads

By Bruce W. Smith  

One of the fastest ways to do a lot of damage to a diesel engine is to cook a turbo by letting the exhaust gas temperature (EGT) get out of control under heavy loads.

That’s just the type of thing that happens when diesel pickups are pulling heavy trailers up long grades in the middle of the summer.

Big load, high boost, in high ambient temperatures for long durations does not a happy turbo-diesel make.

One method to help keep a lid on those extreme EGTs is to cool that fuel-air charge using a water or water-methanol injection system.

The technology has been in use for many decades, being used in fighters during WWII and heavily used in the turbo’d cars of the ‘70s. It’s quite common on big rigs today.

(My first experience with water-injection was when I put Webers and a Shelby-Spearco turbo that used water-injection on my new ’77 Celica GT. It allowed me to run 15psi boost without melting the engine or destroying pistons.)

Cooling Power

Today’s pickup turbo diesels, such as the Duramax 6.6L, respond quite nicely running water/methanol injection to lower operating EGTs – and without the need for additional electronic engine tuning.

A 50/50 water/methanol mix can add as much as a 20 percent boost in power while helping cool down EGTs by hundreds of degrees.

Diesel engine water-injecton cycle diagram. Courtesy of AEM

The downside for the company pickup is it isn’t street legal in a number of states that adhere to the California Air Resources Board (CARB) emissions standards.

On the other hand, water-injection kits, which AEM Performance Electronics has C.A.R.B.-certified, provides similar results for work trucks – and it’s legal in all 50 states.

Water-injection can add as much as  8 percent in power in some situations, lowers EGTs very similar to the water-meth mix, and bumps up towing fuel economy.

Behind Water-Injection

You are probably wondering how water can help improve fuel economy and make power when it’s not a fuel.

You are probably wondering how water injected into your intake system can improve your vehicle’s overall performance.
According to Lawson Mollica of AEM Performance Electronics, when atomized water is injected into the inlet stream on diesel engines under heavy loads and high boost, it delivers a cooling effect that results in a reduction of exhaust gas temperatures.
“While our water/methanol injection systems do provide an increase in power and a reduction in EGTs, they cannot always be run legally on the street in every state.
“Our engineers designed a water injection kit that is California Air Resources Board (CARB) exempt, meaning it is street legal on a multitude of diesel applications.
“This kit allows anyone who wants to reduce EGTs when they tow, or their pickups are heavily loaded, to do so legally if water/methanol injection is not legal on the street in their state,” says Mollica.
Mollica explains that when water vaporizes in the inlet tract it absorbs heat. That shows up on a pyrometer when the injection system kicks in and EGTs drop. Another benefit is that the steam produced from the water injection helps to keep the engine clean — especially the EGR manifold.
AEM 50-state legal water-injection kit for Duramax 6.6L with optional flow and EGT gauges.

A Timely Upgrade

Those are the reasons we had Truck Supply & Outfitter’s Daniel Parker and David Adair install an AEM 50-state legal Water Injection System on our 2008 GMC Dually’s Duramax.

The upgrade like we did it on Big Red takes about six hours. About half of that time R&Ring the intake manifold so it could be drilled to accept the injector, and drilling and installing the EGT probe in the new BD exhaust manifold. The drilling is easy–the R&R not so much!

Note: We upgraded to a BD Diesel performance exhaust manifold ($300) while we had the OE one off to maximize exhaust flow to the turbo and improve power. (See separate how-to.)

The remainder of time is spent running the wiring harness, mounting the optional gauges, installing the pyro sender in the exhaust manifold, and mounting the pump and water tank.

Take my word for it: This is a very cool engine upgrade – in more ways than one.


Special Thanks

AEM Electronics: www.aemelectronics.com; 310-484-2322

BD Diesel Performance; www.dieselperformance.com; 888-841-8884

Truck Supply & Outfitters; www.trucksupplyandutfitters.com; 205-553-4203