MAF - Water or Meth Injection

[JNR]

OK, this may be a silly question, but was thinking about this the other day...

When you use water or (esp.) methanol injection, does this cause any issues with respect to what volume the ECU thinks is there? I mean, you are adding some volume there (beyond what the ECU 'knows' is there) and say when the water turns to steam wouldn't there then essentially have some additional oxygen (from the water) in the mixture? How about methanol since some of it is then fuel? I imagine the air is denser from being cooler (the water content to steam in both types), but I am curious if there is a way to compensate for this, or perhaps there is no issue to be concerned with?

I haven't *heard* of any real problems with WI in respect to this, but wondering if there are some more improvements to be had with better correcting the actual A/F ratio with respect to the ECU...

 

[cheekychimp]

I think you first need to understand the two main types of injection and the purposes for which they are used. The first of these is direct injection essentially straight into the combustion chamber (or as close as you can get) in order to suppress detonation; and the second is injection into the intake tract to cool the charge air.

Now I understand what you are getting at here if we consider intake cooling. You are saying that if the car was running on a cold day we would be sucking cooler air into the intake tract but it would be passing the MAF and so the denser air should be compensated for, but that if we cool the intake tract post MAF we are getting in essence a denser air charge that the ECU knows nothing about, right? I'll come back to this in a second.

First however, let us consider direct port injection. It's a widely misunderstood fact that turbo cars use a lot of fuel to make power. Obviously the faster you want to go the more fuel you burn (well up to a point) but a huge amount of fuel in turbo cars is 'dumped' into the combustion chamber in order to essentially cool the chamber itself and prevent detonation. This is why you have a knock sensor and why tuners add fuel in the fuel map when they see knock. When you inject water directly into the combustion chamber, you are essentially removing the need for all of that additional fuel. In order to make the car run smoothly you actually need to have some fuel management in place so that you can pull fuel or you will bog. With methanol injection you again need to pull fuel to get your correct AFR or you will most certainly go rich, because as you pointed out, methanol is a fuel.

So to answer your question it isn't so much a case of there being improvements to be had by better correcting the A/F ratio but rather that this is something you absolutely MUST do or there simply is no point in doing water or meth injection in the first place.

Now regarding the denser air charge. You can actually inject water as a method of intercooling. Some people have run systems injecting huge amounts of water and using no intercooler at all. But again the point is that you have to tune for this or at best you get mediocre results and at worst you will run into massive bogging issues. Think of it like this. If you inject so little water that it has no effect on your AFR, are you actually achieving anything by doing it in the first place, except possibly steam cleaning your engine? If you are injecting a significant amount of anything (water/methanol/propane) YES it will have an affect on your AFR and if the ECU knows nothing about it, there will be issues, so you SHOULD be tuning for it.

What does commonly happen and the reason you may think no tuning is required, is that people run injection to offset knock (detonation) at higher boost which is the same reason people use race gas. So people 'tune' the system by adjusting nozzle size to compensate for knock or raising boost until they reach the threshold that the injection level can support. Generally, it is much easier to tune your fuel/boost etc to match your injection, rather than trying to get your injection spot on by changing nozzles/injection pressure, volume etc.

Bottom line is you have to do some sort of tuning with any sort of injection PERIOD.

 

[JNR]

Thanks for your input and makes sense. So, the ECU does not 'know' about this extra volume, but should be easy to compensate for in the tuning, *provided* you always run the injection medium (in my case water at say 10 psig). I wonder if there was an easy way to have a dual mode tune, so to speak: one with WI and the other without...

Fwiw, I am talking about injection post MAF, past the intercooler and close to the TB inlet. I would suppose that it would make a difference where you have it (intake tract vs. direct port) in respect to 'tuning' for it, as well as what you're using (water, 50/50 meth-water, pure meth?)...I mean, I'm sure there are several variables/conditions to consider, but I was mainly curious how it would be 'as is' with the extra volume (mass) that the engine would see vs. what the ECU thinks there is. I imagine there is *some* compensation/adaptability with the MAS system (vs. Speed Density), but that is more on a N/A engine...throw in the turbo and its added parameters and sure how well it would adapt to these conditions (to a subtle level of course).

I am planning on pure distilled water. I am a little nervous introducing a flammable substance/mist in the intake system, should a backfire occur. Probably not much of an issue though, being the engine would probably suck it in upon letting off throttle and/or it would escape thru the BOV. Still, makes me nervous /ubbthreads/images/graemlins/smile.gif

 

[curtis]

a 46/54 mix is essentially a 50 /50 mix. The water is there to cool as Paul said cause water has a 4 times great effect of latent heat of evaporation then the meth is for power. Read some where that 70 percent of the fuel burnt in a combustion engine is to do nothing but cool the pistons. Not hard to understand cause aluminum melts at about half of what most combustion chamber events are.

 

[turbowop]

I inject 100% methanol. Works great. I inject enough to run 31ish psi, but not enough that I can't stutterbox the car without it going lean and blowing up.

Mine is setup and tuned in conjunction with my Maftpro and a two stage manual boost controller. When I turn the system on, the boost controller switches to high boost and the Maftpro uses a map that pulls fuel when the meth starts spraying (over 10psi). When turned off, the boost controller reverts to my low boost setting and th Maftpro runs the standard fuel map I have set. The coolest part is I use a factory eco/pwr switch to turn the system on and off. Stealthy.

 

[Tre3zy]

^ thats cool.... ima going to be running meth soon as well....

 

[JNR]

Curtis...yeah, I think that's what my great old friend PO (sarcasm) did on mine when I first got it...that was to just dump a lot of fuel. The good part was being able to run 24 psig on 91 piss gas, lol; bad part was it was always rich! I've since fixed that band aid of his though, but do understand and agree with what you guys are saying with the fuel...

Pigzilla...Ha ha (sorry such a funny name), Mark...That is sort of what I was thinking of with the two different 'settings' so to speak, although I am not familiar with the MAFT Pro, other than hearing the name...Are you running a pass-thru GM unit of sorts? In other words, I wonder how something like that could work with a 3rd gen oem MAS, if at all...Will need to think deeper into this later; too early for such puzzles right now.