2 Strokes and Water Injection

Those who are not familiar, please read the following

Water Injection in General -


Water Injection in 2-stroke Exhausts



In short, you can inject water into the intake tract in a very fine atomized mist, as the water goes from liquid to vapour it will absorb heat in the intake tract (latent heat of vaporization of water is among the highest at over 2200J or heat per gram). Also water helps to smooth out combustion by reducing peak pressures (detonation or pre-ignition) and increases the EFFECTIVE octane (not the chemical octane as water does not contain any chemicals). By means of a programmable CDI you can then alter the timing to allow the mixture to burn more efficiently (generally higher effective octane will allow a bit more timing to allow the mixture more time to burn completely). This results in a higher efficiency and power (many turbo applications use water injection)


Injecting water into the pipe will change the acoustic sound pulse allowing the powerband of the pipe to be broadened. Basically, if a pipe makes most of its power in the upper revs (6000RPM and up) one can benefit from water injection in the lower revs (3000RPM to 5800RPM, allow some RPM for exhaust to heat up again) and this will significantly increase the Torque.

I have a 2006 YZ125, quite a lot of time on my hands to tinker with stuff and am studying engineering in school and will be specializing in race engine design. I would like to know if anyone can offer me any advice of how to control this system.

I have access to a brake dyno, so I will be able to dyno tune the engine. I am going to be purchasing a programmable CDI unit, which will allow me to change the timing curves accordingly (I have been instructed to be extremely careful with this as timing adjustments are very critical especially in the 2-stroke).

In order to introduce the water into the intake tract I am looking at possibly using a Dial-A-Jet system


These are unique in design because they activate the fuel (or water) flow by means of engine vaccuum as well as acoustic pulses from the engine (lean condition producing higher frequency sound waves -- pulling in more fuel, rich condition being lower frequency -- pulling in less fuel). It will need an external float bowl to store the water but this type of system seems to break apart the fuel (water) very well and would provide the proper atomization that I would need.

As for the exhaust, I would need to use some type of controller which turns on the water at a given RPM and then shuts off the water at a given RPM. Many say that also a certain throttle position for activation would be beneficial as I wouldn't want the system to engage upon deceleration (when I do not require the power, it would just waste the water). Basically I would tap a brass jet into the exhaust and run a stainless line for the first few inches to keep everything from melting, run this to a very small pump (windshield washer fluid pump would work).

I've seen these MSD water injection kits for jetskis, these are generally multi cylinder but I'm sure they would work. Just not sure how its able to read the RPM


Not exactly sure if this would be the best method on a bike, but at least an option.

I have heard of CDIs with outputs that would allow control of a switch, but can not find any information on them. The one that I heard of was a 3D Wolf CDI but I'm pretty sure they're out of business. I have some experience with electronics and whatnot, but I don't really want to rig up a hall effect sensor and missing tooth amplifier setup just to get an RPM readout and still have to find a way make a processor read this and send a command to energize a selenoid.

Does anyone have any ideas of how to control the water injection in the exhaust in an effective and hopefully affordable manner? I'm sure there is a simple way to do this, as even spark plug wire surrounding hour meters are able to provide RPM feeback.

Please only post with helpful information, I am looking for some engineers inputs or people with this type of experience as I have posted this in the engineering and technology part of the forum.

Thank you for reading all of this!

No one? :(

No one? :(

It's interesting, and I want to learn more, but have nothing to add.

sounds like you need a window switch but also a switch to tell when the throttle is open so the circuit doesnt complete while you are decellerating, like you said


your bike already knows what RPM it is running at, you just need to figure out which wire that is and how the signal works.

sorry, i dont have much useful info pertaining to this. it sounds like a good project though.

- Fellow ME student

Simplistically, in a system such as introduced on several warbirds in the 1940's, use a pressure controlled switch or solenoid valve controlled by boost pressure or throttle position. More elegantly, a PM solenoid driven by an ECU.

Thank you grayracer and joeman2055

The only problem with referencing to boost pressure (or just vaccuum pressure as this would be naturally aspirated) is that in a single cylinder application the manifold air pressure pulses, as opposed to an automotive or multicylinder application where the manifold pressure reading stays much more consistent.

Looks like I'd be able to do this with a carburetor that uses TPS. Unfortunately my carburetor doesn't but it looks as though the YZ250 uses TPS and a power jet as well (not sure what I think about the power jet yet because I don't know too much about them but programmable CDI's offer adjustable power jet operation).

With the TPS I could get a switch to activate when a certain voltage passes through, I'm not sure what kind of switch this is called, though I don't think it would be too difficult to find out.

The water reservoir, pump, and probably a 9V small battery will be used and everything will have to be mounted in the airbox, which makes me think I may have to find a way to get some room in there. Darn airfilter takes up most of the space LOL. I still have to find out if a YZ250 carburetor will actually fit in the space that I have.

And grayracer, I would love to use an ECU but it just doesn't seem like it would be worth the investment, especially if I'm only controlling very very few parameters and outputs. Especially if everything could be made very functional using a more basic means, although the Microsquirt (made by Bowling and Grippo) looks pretty tempting, maybe in a fuel injected bike though.

TPS units are almost universally potentiometers, so they lend themselves well to use with digital stuff. OTOH, a simple micro switch set up to contact the throttle linkage at WOT would be minimally serviceable as a prototyping kind of thing.

I am all for thinking outside the box. But By the time you add a tank, lines injection pump, I think the added complexity and weight would negate the benefits. And I hate being a negative Nellie, I am by no means a engineer, just my opinion. Would be glad to hear it was/is worth it. I remember a drag boat running in blown gas that had a small tank filled with alcholol (told everyone it was water) That used maifold pressure (boost) to pressurize a small tank so that at a certain amount of boost the poppet opened and started spraying the "water" in the injecter to help control detonation. That boat set all the records and was undefeated before it crashed.

Water and alcohol were used for detonation suppression as an evaporative intake charge coolant in aircraft for a very long time beginning with the WWII era, with alcohol being the more effective. The main issue there was not so much the momentary load the engine was placed under, but the length of time it operated at such loads, and the associated heat build up from that. In the drag boat example, it's more a matter of being able to run the ignition as far advanced as desired under the boost pressure you want without setting off an explosion of some kind.

Sidebar: one of the first operational uses of nitrous oxide injection was in the Messerschmitt Bf109E. It was an attempt to juice the bird up so as to climb to the altitudes of the allied B17's quicker.

Thank you for the concern and the advice ben

Very cool info grayracer

My thoughts: I will not be implementing it all at once. I will be doing it gradually, I am first going to start off injecting water through the carb, see how the performance is. The bike is a 144 and they are notorious for cooling problems, that is where this interest ultimately developed. As for the weight issue, water will be injected at approximately 1/10th the ratio of that of fuel or less (some say 1/20th). That being said, the water tank will not have to be big by any means, probably similar sized to a water bottle (500ml). It will only have to last a 20 minute moto. Also, a windshield washer pump weighs around 500 grams, a battery maybe 50g. I don't expect overall weight to increase too much. Don't forget, I'm also running a 125, these things are 189 pounds dry weight, I have a bit of room for movement if need be.

After looking into a TPS carburetor I'm thinking it will be too much hassle, because it has to get power from the CDI in order to produce any signal, and if I were to use an aftermarket CDI it might get a little bit complicated. I like the idea of just using a contact for a certain throttle position on the slide or cable, the whole benefit of water injection through the exhaust is the midrange and lower end performance so I'd probably aim for half throttle or something.

At first I can just have it run to the window switch and run wasted water on deceleration, if the performance improvements are noticable in the acceleration I will try to refine it further from there. Whats good about this is that I can use it is a school project, which would be another motivating factor. Having access to a dyno will also help me to see if the gains that I feel are real or only in my mind. I will report with updates.

Just run it on E85 or 90. More compression less detonation = more power

Just run it on E85 or 90. More compression less detonation = more power

Or methanol.

There was a guy who used a Mrd jetski mechanical injection setup on a yz250 with methanol he was saying it was a monster.

I may possibly mix water with methanol at 50/50.

I don't like the idea of ethanol. Methanol has higher octane, burns coolers, higher latency, and is much easier to attain and is much less expensive. Water cools the best by far though, and is even cheaper and easier to find (even distilled). Methanol is also a fuel which will alter jetting if I choose not to run the setup or run dry, water doesn't change the jetting requirements.

One thing about that is that methanol injection as a detonation suppressant requires a fairly small amount of added alcohol, and methanol can be run very rich. The few times I've run into these systems they were set up jetted correctly on gas without the injection. When the methanol was dumped in on top, it just didn't matter that much, but of course, the amount used would determine much of that.

If the engine is set up to really take advantage of water injection, having that run dry is going to affect things, too, whether the jetting changes or not.

Hi there, just had a read through this, and from what I've read in the past a good result can be had from injecting water to supress detonation, but the volumes of water need to be be tightly controlled and proportional to fuel air/flow. With this in mind, have you considered setting up some a programmable ecu, along with fuel pump and injectors as per a fuel injection system, and then running a water/methanol mix? The only issue i could see would be if the fuel pump would suffer from running water (corrosion, lubrication issues). That way you would have a fully mappable water injection system, where you could closely control water volumes and injection timing at all throttle and rev conditions.

Just an idea....

I also have a vague memory of water injection being injected into the exhaust port, with the main intention of this being to cool exhaust gasses at certain parts of the rev range. The cooler gases act to change the speed of reflected pulses in the expansion chamber, and therefore give you a means to effectively change the tuned length of the exhaust system, meaning the power band can be moved up and down the rev range. In a clever system the water could be metered out according to the rpm, and thus keep the system "on pipe" for much longer, like an infinite powervalve....in theory!

could be quite interesting to get working :thumbsup:

Thank you very much for all of the input guys.

And you are absolutely right about the conditions changing if I were to run dry. Actually, vortex and other ECU companies offer external adjustment of maps via a handle bar switch or ECU mounted dial with numbers. If I were to run dry I could just go back to a base tune. I will obviously be keeping my eye on the system to make sure I know when to switch,

Also, my interest is leaning me towards specifically water, it would make the system less complicated. I will run a mix of this http://www.klotzlube.com/techsheet.asp?ID=51 product in order for the water to contain lubricating properties and not displacing oil too much. Also, I live in very humid weather which in Southwestern Ontario in the summer. Very often 100 percent humidity and this is where the water is saturated with water already, in which case my injected water likely won't vaporize completely, or at least as easily.

Also numbhands, I can run this water injection in a way that it is proportional to engine load, which is EXACTLY how a carburetor works. Pretty cool concept, a lot of guys actually run these for water/meth setups in EFI engines because of their convenience.

Dial a Jet


Fuel injection would be sweet, but maybe like a year from now and I could tap into the block and do direct injection but that's only a dream for now. Would love to make this a competitive bike as I will be racing in the Open Expert class at my local club (smaller club) and it would be pretty cool to see a small bore up to speed.

Also for the exhaust injection, it would be nice to have it vary the amount of water so that the powerband could be broadened to even a greater extent, but controlling that would be pretty tough. Double, but tough.

Hey guys, I'm opening this thread back up. I am CR85Racer12 this is just my other account, I couldn't find the password for that other account (its almost a 10 year old account)

So I'm in the process of making a quick machine which is hopefully still nice and light. It will be a 2005 YZ167 with the exhaust water injection as mentioned in the earlier posts. Here is how I am planning to do it, looking for some advice to see what other people with an engineer's mindset think.

1) I will be welding a bung onto the exhaust pipe right near the cylinder and attaching a very tiny nozzle (rated at 35cc / minute at 100psi pressure) I have the nozzles already

2) Will be using a small, high pressure electric motor. Same type of pump I am using on my turbo Honda civic for water injection only smaller.  

It is small enough to fit under the engine, strapped onto a skidplate, provides high pressure and requires 35 watts max

3) Running a YZ250 Carb (same 38mm, Powerjet disabled) so that I can use the TPS for a load parameter

4) Will be using an Arduino Nano to read the RPM as well as the TPS, and then create a map that uses pulse-width modulation to control the voltage at the pump, and therefore the pressure at the nozzles (basically high pressure at low rpms/high load and tapering off in the higher rpms)

5) Since I will need to power the arduino (which takes only a couple watts) and the pump which takes 35W I will need a stator that can handle that kind of power demand. Options are to use a Steahly stator meant to power headlights, or to somehow modify a WR250F stator to fit to this bike. Also a possibility to just have the stator rewound to suit the increased demand, although I'm not sure this is possible as there is limited space as it is and my guess would be more coils would be required for more power?

Here is where it gets tricky

6) For the water reservoir I have 2 options, I can either section off part of the gas taken by modifying it considerably and allowing it to hold a small volume of water (my guess would be between 500mL and 1000mL)
I can get a oversized high radiator for the left side, and then convert the right radiator into a water reservoir, however this may cause cooling issuses, I also may be able to get a heavier duty water pump to move the water faster to help with cooling. Definitely looking for some opinions here

7) Lastly I will be using a water-solenoid that will be switched when the RPM's get high enough that exhaust water injection is no longer necessary, the solenoid will direct the water flow to my other mini injector (again 35cc/min) in the intake tract. It will produce an extremely atomized most which will help to cool down the intake tract and give a few ponies in the upper RPM range as well as help with the possibility of knock or detonation. I've been reading about 2 strokes and have been reading that the excessive heat really limits them in the upper RPM range as the piston is firing with every other stroke, the heat never has a chance to "escape" so I'm hoping that the water can help with this. And I know that detonation is most likely to occur at peak torque which will be in the midrange but this will be when the exhaust water is spraying the hardest, and some of the water will be pushed back into the combustion chamber by the returning sound wave, so that should also help with detonation at this rpm range.

I just got the 167cc motor and I have a few of the parts and the rest are soon to come. Yes the 167 is already quite fast but I want this thing to be blistering fast, faster than any small bore 2-stroke. Porting is set up for mid-top and I have the most mid-top combustion chamber I could find (FMF SST) which will provide power in the upper range and the water will help in the mid range so that this bike should have a very impressive powerband.

Don't worry I am riding the bike for the rest of the season with the 167cc and won't be really diving into this until winter forces me to stop riding but that really is not far away now, we will have snow in the next month or two.

Anybody familiar with creating maps using arduino or microcontrollers? Anyone have any suggestions for the water reservoir and if eliminating a will and depending on one oversized rad to provide all of the cooling? Don't forget that the water is considered "liquid intercooling", I guess I can really only find out through testing here.  

Any suggestions would be awesome, thanks guys


I know all about water injection into a pipe! I own a Jetski shop and factory race pipes have a set up with solenoid that inject water into the pipe to change to power curve by changing the temp of the exhaust going thru the chamber. It's like having a pipe that's adjustable.. I haven't tried this ..but you can use dry ice to!! Even on your intake .. Trying to cool it down .. I also know that it does works because I have the first one ever made and it does work. We used it to cool the fuel going into the motor which condenses the fuel plus cools the intake and cylinder. If you have any questions just ask.. I'll have the answer.

When I was around water injection we used a drag race rpm solenoid box. Had a start and end rpm with pills. Also depending on what type of power valve you have it can completely remove the effect. On a Suzuki the power valve had to be in the high rpm position to work.

As I remember the nozzle in the pipe was simply main jets. Allowed tuning of the water volume.

very interesting and informative.love this stuff.

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