100 KPa is atmospheric pressure which is 0 on your boost gage. So anything below it, such as 20 KPa is a vacuum.

 

So what about running pump+meth? Do the same principals apply or should you be aiming for a different range?

 

This is another tricky question.

Personally I like to run a water/methanol mixture, with a bit more water than methanol, like a 60% 40% mixture.

There are really two approaches to injection as far as tuning goes as I see it. But before I describe them, I would like to take a chance to talk about injection in general, as some people know a lot about it and some do not.

It all goes back the the principle that we only use 1 part fuel for 14.7 parts air during combustion. If there is less air than 14.7 part per 1 part fuel, we have a rich condition. Not all of this extra fuel will be burned during combustion. It is use to control combustion temperatures and hence cool the mixture. The more fuel you add past where the engine makes the most power between 12:1 and 13:1, the slower the flame propagation speed becomes.

-- Latent Heat of Vaporization is a term used to describe how much heat energy per unit mass it take to take that unit of mass from a liquid to a vapor state.

Basically, this says that it takes a certain amount of energy (heat) to make a liquid turn to a gas.

For those confused by the units, dont worry about it, and just look at the numbers that I am about to list. I am a mech. engineer and I like SI units instead of english, but again, dont worry about the units.


For XXXXX it takes xxxxx amount of heat energy to change this mass from water to liquid.

Gasoline..........350 KJ/Kg
Alcohol............896 KJ/Kg
Ethanol...........904 KJ/Kg
Methanol........1109 KJ/Kg
Water.............2257 KJ/Kg

As you can see, gasoline takes the least amount of heat energy to do this. The more heat it takes, the more cooling effect.

The Primary Reason that we inject our car is for cooling, no matter whether we inject alcohol or methanol (both of which are fuels). It is a common misconception to think that the primary reason we inject our car is for the added "octane". While this does happen, only a small percent of what is injected actually boosts the octane rating of the total mixture in the cylinder (I have heard that it is somewhere around 15%). Again, the reason is to help keep combustion temps under control.

So now back to the tuning approaches with injection.

Note: It is assumed that timing is being adjusted to MBT for all of the following strategies.

1) One can argue that because we are injecting a fluid that cools the combustion process much better than the excess gas we are throwing in, why not just take away some gas since it is no longer needed for cooling.

This is a good strategy. One important thing to remember though is that an engine will make about the same amount of power within a pretty big range of AFR's, but once outside of this window, the power will drop off quickly.

Since an engine makes the best power between 12:1 and 13:1 AFR, with this method, you can lean the car out to somewhere between the two. When following this method, I typically shoot for an AFR near 12.2:1. Then ignition can be advanced to MBT.

........ But what happens if a pump fails, or we run out of spray?
We will be running much to lean for the amount of ignition advance we are using, which will pretty much cause instant irregular combustion, aka knock, detonation etc. Not Good. What we need is a fail safe. There are many forms, some of which will alert you that there is a problem with the system, and some that can alter to fuel and ignition maps back to an acceptable level for running with out injection. Clearly this depends on what ecu you are using and is not the case with the factory Ecu currently (mabey the ecu gurus will help this to happen some time ).



2) The other approach I consider good is running the same AFR you would tune to without injection and adjusting the timing to MBT with the spray on.

This will allow for quite a bit more timing advance (higher than strategie #1 typically), but again if something with the system fails, you will still be running way to much timing for the AFR without injection. Again I encourage a fail safe.


-- Which is better?
Well, I think it really depends on the cars set up, purpose, and mods. With a pump gas street car, with moderate modifications, I would probably go with #2, running a Target AFR from right before peak torque to redline of about 11.5:1 and advance timing to MBT. But then again it depends.

Remember that injection does a very good job of suppressing detonation, and can allow you to run much more aggressive fuel and ignition. It is an excellent way to get more power out of your setup and is a relatively inexpensive mod, but it is important to be careful as always! Remember to check those reservoirs!

I hope that this has helped some of you guys out, and answered your question NIevo.

 

Good info. I am copying all that into a text file to chew over. Thanks Kyle.

 

Dont confuse the guy. 12-12.5 makes more power than 14.7, cause it burns faster. So it shoud probably read "anything richer than 12.5 is used for cooling".

 

nor even sure it burns faster, but it does ensure that every o2 molecule has an easy to find partner to mate with. although 14.7 is more perfect, in the cylinder things get hectic, maybe some oxygen doesn't have time to find some fuel so we add a few extra partners for the oxygen boys to mate with.

 

This is correct, I apologize. I try to carefully read and reread through my post many times before I post them up, but It was very late last night when I wrote this. And somethings sound good when your half asleep. Correction noted and fixed.