Ask Sarah- Does water injection work?
Sarah Forst
Ask Sarah- Does water injection work?

Hey Sarah,

I have a turbocharged 1995 Integra GS-R with a T3/T4.  I usually set the boost around 8-10psi but sometimes I get up to 14psi.  I still have a stock ignition.  Is this boost too high for 91 octane?  One of my friends said I should install a water injection system, but doesn’t that just kill power?  Can you recommend any water injection systems?


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Detonation or knock can quickly kill an engine.  The tendency of an engine to knock is affected by many factors including ambient air conditions, engine design such as quench in the combustion chamber, spark plug location, and compression ratio, engine temperature, air fuel ratio and the fuel octane.  Turbochargers force more air and fuel into the cylinders making the engine run hotter, the higher the boost pressure, the higher the cylinder pressure and temperature will be.  This causes more stress on the engine’s internals and making it more prone to knock.  The GSR engine has 10:1 compression ratio, fine in its naturally aspirated form but fairly high for a boosted motor.  If you have effective engine management and good tuning, 10 psi should be ok for pump gas but 14 psi would be pushing it on 91 octane.

AEM Water injection system
AEM's water injection system has many tuning variables, from onset boost pressure, to max flow boost pressure to volume.  This makes the AEM system very flexible.

Start by checking out your entire ignition system (plugs, plug wires, and distributor cap and rotor) to make sure everything is in good operating condition.  The stock ignition system should be fine until about 10psi as long as you are using spark plugs one to two heat ranges colder than stock.  Colder plugs help prevent detonation by keeping the plug center electrode from getting too hot.  Gap each of the spark plugs at around 0.030 inches and close the gap in 0.005 inch increments if you have any misfire.  You may need to gap them as low as 0.020 inches, especially for higher boost pressures.  With water injection and the proper plugs and gap, the stock ignition should work fine up to 14psi, but you should consider a high performance ignition system such as the MSD 6A if you want to go any higher.

Water injection is meant to suppress detonation caused by the increase in combustion temperature and pressure in turbo or supercharged engines.  Water has a very high specific – and latent – heat capacity, meaning it takes a lot of energy to heat water up.  This makes it an excellent liquid for regulating excess heat under certain operating conditions.  The water injected into the intake stream vaporizes and acts as a coolant, cooling your intake charge and producing cooler combustion temps, making the engine less prone to pre-ignition or detonation.  These conditions are especially common in forced induction engines, where exhaust temperatures can run much higher.  Most water injection systems can be programmed to come on at a set boost pressure, causing a jet to spray water into the intake system. 

AEM water injection nozzle
AEM's system has the water nozzle and check valve built into one unit.  The AEM system comes with three nozzles, small 130cc/min, medium 315, cc/min and large 550 cc/min.   The flow can also be tuned within these parameters by the pump controller.

Most forced induction production cars control combustion temperatures by dumping additional fuel to act as a coolant but if you go too rich, the flame burns slowly and incompletely causing you to lose power.  The point of diminishing returns for detonation suppression is around 10:1 although power will start to be diminished anywhere richer than 12.5:1 or so. A good water injection system keeps from having to dump more fuel, leaving your air/fuel ratio unaffected.  Although in some conditions lower combustion temperatures will reduce power slightly, by suppressing detonation you can raise boost, increase the timing advance, lean out your air/fuel ratio, or a combination of all three to produce more power.  Some other advantages of water injection are it cleans the engine of carbon deposits and sludge, provides the advantages on higher octane fuel out of lower octane, and the lower combustion temperatures due to water injection also lowers NOx emissions.

I recommend ERL Aquamist water injection systems.  Their jets atomize the water, which helps with distribution and improves vaporization.  Stay away from cheap water injection systems that use non-atomizer nozzles.  This will cause unequal distribution and bog the engine down.  Aquamist’s water injection system is tunable with jets ranging in sizes from 0.4mm to 1.0mm.   I also recommend AEM’s system as it is easily tunable for flow volume and injection onset point.  With its optional flow meter you can know exactly how much water it is flowing into the engine in cc’s per minute.

Aquamist water injection water pump
The Aquamist pump is very compact, good for tight locations.


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