Water Injection - The True Story

The purpose of this page is to help people with an interest in water injection, to learn the real story behind it's merits and uses. Every now and then, on the GT-Four mailing list, I see a message come up, in which someone has mentioned that Mr."X" from "Yyyy" Tuning Shop (I won't name any names here) has told him water injection is useless, or a waste of time, or worse, will cause his car to lose power. I almost fell into the trap of believing this nonsense, and missed out, on what I consider an excellent modification, which has proved itself on my car. How do I know it proved itself? The absence of detonation, reviewing data logs of intake air temps, and a Toyota Celica GT-Four, with over 300 hp, still using the stock intercooler, don't lie, and have no biases or ulterior motives.

Note: Before I begin, I would like to make a few things clear.
1. In my opinion the only true water injection systems are ERL's Aquamist systems. There are plenty of cheap systems out there that have probably helped to fuel the controversy over water injection, by the very nature of their inadequate equipment. Like any other modifications, water injection systems needs to be developed and manufactured to do their job correctly.
2. I am in no way affiliated with ERL. Just like other manufacturers whom I endorse on my site, for example Autronic, I believe in the quality and functionality of their equipment, and through the use of the products can attest to their performance.
3. There have been a few do-it-yourself water injection projects that have popped up every now and then on the web, and on a few mailing lists. I strongly recommend against trying to build such systems. Adequate water pressure, jet size, spray pattern, jet location, and water quantities are essential to a system functioning correctly. One member of the GT-Four mailing list, on the recommendation on someone from the web, placed a "home made" jet pre turbo, (something which is not advised), and used a windshield washer pump, which lead to the destruction of the turbo compressor wheel in just one day.

Does Water Injection Really Work?

It seems some people want to categorize water injection with a "snake oil". These people are either ignorant to the facts and long proven history of water injection, or could probably be tuners eager to put your hard earned cash in their pockets for lots of parts you don't really need. So do we trust these people blindly, and dismiss water injection as a valid modification? Me personally, I like facts, plain, undisputed, documented facts. Theory and opinions are good to hear, and a great place to start, but left unchecked, and with no real world testing, it would still be a fact that the Earth is flat. I got quite a bit of negative opinions, along with the positive opinions, on water injection when I was interested in using it, yet no one with the negative opinions had any real information. I was very surprised when a few well respected people in the tuning arena told me it was a waste of time, yet others just as respected, either said they knew little about it, or believed in it's merit as a valid modification. Clearly, water injection was controversial. That is why I spent over three months researching water injection before I purchased it. From it's first trial in 1900 by an engineer named Benki, to the US Air Force, Royal Air Force and Luftwaffe aircraft during World War II, to Ferrari's use of it in Formula One in the 1980's, right up to the present use on the WRC cars. Just the fact alone that World Rally Cars use water injection should be proof enough that it is not  a "snake oil", unless you are willing to believe that manufacturers, such as Subaru, Ford, Toyota etc., with million dollar plus budgets for these competition cars, know less than your local tuning shop guru. I found lot's of actual testing that confirms it's benefits, and while I have also found quite a few statements, and opinions against it, I am yet to find one actual test showing these negative aspects claimed. Now compare that with the amount of positive present day, and historical, documented facts on water injection, and you discover that water injection isn't controversial when it comes to the facts. All of this only goes to prove, the best way to make decisions, is to be informed, and not just by what Mr.X or Mr.Y says, but by real evidence, as in the results of real world documented experiences and tests.

Water Injections Role On Modified Cars

There are two main approaches to modifying a turbo car. One is the average person who just wants a little more power, and the other is the guy that wants to go all out. Aquamist is ideal, and the best bang for the buck, for the the guy that just wants a little extra from his turbo car. Aquamist is also an excellent complement to a "no holds barred" type modification.

Let's first examine the most common of the two, the guy who doesn't have very deep pockets, but wants a little more fun, with the equation being fun=more power. The first thing he's going to want to do is, you guessed it, raise the boost pressure. He soon discovers that his car isn't running that well. Why? Well, it will usually be caused by some, if not all of the following. The ECU's internal fuel and ignition maps don't extend to the boost he is running, so the mixture is getting a little lean, and there is bit too much advance. The turbo (adequately sized by the manufacturer for stock boost pressures) is no longer running within it's best efficiency range, hence the compression process is creating unwanted heat. The intercooler (also adequately sized by the manufacturer for stock boost pressures), isn't efficient enough to reduce intake temps to an adequate level.  He now must find a way to solve these problems.

There are two ways he can go. The first is to replace/upgrade the turbo, replace the intercooler, and invest in some some sort of add on fuel computer, and while not necessary in some cases (dependant on the internal characteristics of the engine, and the timing maps), invest in an add on ignition computer. Now remember, this is for the majority of people who just want a little extra boost. O.K., let's look at the bang for the buck, and I will be very conservative with prices (all in U.S. dollars).

Turbo Upgrade (replacement will more than likely be well over the $1,000.00 mark)  $500.00
Intercooler $500.00
Fuel computer $500.00
Ignition computer $500.00

That's $2,000.00, ($1,500.00 without the ignition computer) and I doubt you will be able to get the above for those prices. Well, that's a bit expensive, but wait, these things don't install themselves. So let's throw in another $500.00 for installation and tuning your add on computers, and that is cheap. From the time you install the add on fuel computer, you will need to tune it with a proper wide band A/F ratio meter, so you are most likely going to end up at a dyno facility. So the final conservative figure is $2,500.00.....ouch.....that 5 psi increase from 8 psi, cost you more than you thought. Also, watch out for errors that can be made with these types of  mods. Don't add that larger turbo and crank it to your desired boost increase pressure on the stock turbo, because the cfm on the larger turbo will be higher than the cfm on the smaller turbo at the same pressure. Fuel computer....ohh boy.....you can really do some damage with those things. My advise, only increase fuel, as running rich won't kill your engine, but unless you have a wide band O2 sensor and high end A/F ratio meter, don't lean it out.

The second way is water injection, and....well....nothing else. How? Because of the wonderful properties of a virtually free liquid called water. Let's take it step by step.

Your turbo strayed from it's best efficiency, hence more heat, and your intercooler isn't efficient enough to bring the charge air temp back down to acceptable levels. How will water injection help that? Simple, because of water's high amount of latent heat, which is a fact. This process is used on World Rally Cars, and has been clearly proven to work. But what about fuel and ignition? Here's more good news, the water injection will also raise the knock limit on the engine. This is where the skeptics will chime in and say, no way. Unfortunately for the skeptics, this too, has been proven by Saab, when they took a 2.3 litre engine to approx 220 hp, with a curve that only barely dipped at high rpm,  on a mixture of 14.7-1, no that's not a typo, and you read it right, 220 hp at stoichiometric. The most they could get out of the engine without water injection, at 14.7-1, was around 160 hp, and the hp rapidly dropped off at higher rpms. O.K., but what about ignition timing? If your timing is a little to advanced for that boost level, knock might occur. Again water injection will help. This has been proven almost fifty years ago, by J.Jalbert in 1952. He was the director of a company in France called Compagnie des Moteurs a Combustion, and when he did some tests with water injection, he found that with 65 octane gas, he could raise the compression ratio from 6:1 to 10:1. Since increasing boost is like increasing compression, and increasing compression requires the use of higher octane fuel,  ignition retard, or fuel dumping, it's clear to see that water injection will allow for extra timing advance. A side note here. Timing advance will not usually be a problem, as most manufacturers use very conservative timing figures. Now for the cost. An Aquamist water injection system will set you back approx $500.00 to $800.00 depending on which system you choose. Can you say bang for the buck?

Here it comes, the big turbo, large intercooler, more injectors, add on electronics people will be warning you how dangerous water injection can be. They will tell you if it fails, or if the water runs out, your engine will blow up. First off, the ERL Aquamist systems are built to high quality, and aren't prone to failure. Mine has been working for over two years, and I have never had a problem. Of course nothing is immune to failure, but almost all modern, and even not so modern turbo cars, have something called a knock sensor. The manufacturers realize that even a bad tank of fuel, amongst many other things, can cause knock, so to safeguard the engine they install a device called a knock sensor, which informs the ECU of the presence of knock, and the ECU in turn, winds back the ignition advance to save the engine. So if your water injection system does fail, you will realize something is wrong when the car no longer pulls as it should, but the need for a rebuild is highly unlikely. However, even if the vehicle doesn't have a knock sensor, ERL has some great safeguard suggestions on their website, such as ways to reduce boost if the water injection fails or the tank runs low, low tank level switches, and warning LEDs.

Now we can move onto the guy with the deep pockets, that wants to go all out.

You have built a monster, with a large turbo, huge intercooler, higher cc/min injectors, upgraded high pressure/volume pump, programmable ECU, cams, strengthened the bottom end, and have ported and polished everything, and are now running 30 psi, and your latest dyno figures show 450 hp. However, wouldn't it be great to ensure that 450 hp remained consistent when you take it out on the road/track? You find you take it out and sometimes it feels 100%, and sometimes it doesn't quite feel 100%. The likely reason for this, would be a good ECU tuner. Huh? That doesn't make sense. Actually it does. Most good engine management systems will have an "air retard compensation map". The programmer will add more retard, as needed, as the air intake temperature increases.  The net result will be a power output drop off, as intake temps rise. But I have a huge intercooler you say, how could my intake temps increase? Lot's of common and not so common reasons. Things like changes in ambient temperature, lots of tight cornering where air flow over the intercooler is slow, to the unlikely, like debris in the intercooler. So how will water injection help? You could purchase the System2C, which can be controlled by most aftermarket engine management systems that have a "PWM" output, that's mappable in the software. You set it up so that as soon as your ideal air intake temperature is exceeded, the system starts injection, to keep the air intake temp ideal. For example, your ideal air temperature is 40ºC (104ºF), as soon as this is exceeded the water injection commences, and stops as the temperature drops back to 40ºC (104ºF). It's as simple as that. Ooops, here come the "engine will blow up if water injection fails" people. Remember that "air retard compensation map", well, it is still there, and if the water injection does fail, or your tank runs out of water, the computer will start to retard the timing if air intake temps increase. Again low tank level switches can be used to reduce boost as an extra safeguard.

Aside from the benefits water injection offers to modified cars, it can also offer benefits to stock cars. An example of this would be a situation where the octane rating of the fuel where you live is lower than your car's octane requirements. This is happening more now than before, with the increased export of used Japanese Domestic market cars to other countries. Japan uses 100 RON octane fuel, and as such their domestic market cars, are designed to suit this high octane rating. By using water injection, you will effectively raise the knock limit of the engine (the determining factor for octane requirement), allowing your vehicle to operate with a lower octane requirement.


Having dealt with many different tuners, the one thing I have discovered, is that you can't always take what they say without question. Some tuners are very set in their ways, and are stubborn to accept new and renewed technologies, and remain ignorant to them, until wide spread acceptance gives them no choice. Some are more concerned with putting your hard earned money in their pockets, trying to convince you that you need a lot of equipment you don't really need to satisfy your horsepower goals. Armed with this information, you should take the initiative to investigate a modification that you may be interested in. The web is a wonderful source of information, and it is free. You can look for books on the subject. You can call other tuners and get their opinions. One of the best sources can be actual people who have tried the particular modification. For example, everyone on the GT-Four list that has installed an ERL Aquamist System has been satisfied with the results. One member even posted dyno results, showing a sizeable increase of about 15 hp with the system. Being thorough, will not only stop you from passing up on a potentially beneficial modification, but it will also help you not to fall into the trap of buying some of the many "gimmicks" on the market.

This page was created by Dennis Heath.
If you should wish to ask a question about the GT-Four/All-Trac, you can join the GT-Four Mailing List, where I, and many others with GT-Four's, might have your answer. For information on joining go to http://www.egroups.com

Please note that I am not a mechanic by trade, and that any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this site, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here.