proper A/F target with alky/impact on WB readings

[quick-ls1]

What A/F ratio do you guys target at full boost when you are running methanol injection?

I have noticed that I can go quite a bit leaner than normal with alky injection, but I'm still a little confused about how the methanol impacts the WB 02 readings.

Normal gas is most chemically efficient at 14.7:1
Methanol is most efficient at something like 7:1

Most people generally target 12:1 or lower on high boost applications with just gasoline to get the most out of it. What should the target be with a mix of the two?

I’m assuming the typical 02 sensor has to be calibrated with a specific fuel in mind. It reads oxygen content in the exhaust stream and then the controller determines what the original a/f was based on this reading and the stioch numbers for the fuel. In other words, It seems like the controller must be calibrated for a specific fuel.

It seems to me that the methanol would make the WB read leaner even though the actual a/f ratio was richer. Am I missing something?

 

[Razor]

There is one more piece to the puzzle, thats EGT. And using EGT's for tuning, along with the WB, will allow you to sort the car out.

Air fuel is air fuel. The leaner you make the mixture, the more power thats to be had. So 12:1 technically should make more power than 10:1. Tho some motors may like the 10:1 AFR, and make the most power at that level.

You'll have to play with your fuel tables at the dyno or trak and find whats best for your particular combination. Tho a nice crisp tune would be in the 11.3-5:1 AFR range. And should get you really close.

I tune with an EGT meter, monitoring knock retard. The higher I can run my EGT meter without getting KR, typically the faster/more MPH the motor will make.

 

[quick-ls1]

Air fuel is air fuel. The leaner you make the mixture, the more power thats to be had. So 12:1 technically should make more power than 10:1.

Ok, I think I figured it out.

Here is what I was thinking:

You take two containers and fill one with 02 and one with fuel. You set them up with a 14.7:1 ratio of Air to fuel. Now if you could combust this and send it to a WB the reading would be 2.5v 14:7:1 right?

Now, remove half the fuel and replace it with meth. The physical ratio would still be 14.7:1, but what happens when you combust it and send it to the WB. The WB will read much leaner since the meth will leave behind more 02 than the fuel would.

The number from the WB is no longer an accurate physical ratio, but it is a valid index. If the WB says 11.0:1 and you are mixing fuels it is not really 11.0:1 physically , but it is still a few points rich of stioch and a useful index.

 

[Razor]

I think your getting a handle. But you have to remeber this is all under the assumption you are injecting X amount of alcohol to your Y in fuel. This is where the variables come into play. Especially due to changes in pump pressure, INJ PW commanded by your ECU, ratio of alcohol being sprayed(assumming straight alky), outside air temps, humidity, etc. probably too numerous to figure out.

An EGT guage rocks in these applications becuase it doesnt care. All it can do is display temp it sees. Now using a WB with an EGT you now have a system of checks and balances. Whereby if your EGT can be correllated to your AFR. And if your AFR is stable and the EGT climbs, its probably due to knock/detonation occurring. if you can run your AFR nice and lean and get no Knock, you will see some serious power.

I have found upping the flow rates of methanol through the motor where fuel is being replaced, has allowed the motor to be run way way leaner without knock retard. I cant tell you how many 1700+EGTs passes i've run with zero KR at high boost levels. All in the name of science