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Air Fuel A/F Ratio Basics | Wideband vs Narrow O2 sensor


I found this simple explanation informative..



One the most important aspects of the combustion motor is the air to fuel ratio in the cylinder. Like all things that explode, having the proper amount of combustible fuel to the amount of air to sustain the burn is important. Having lots of air but no fuel will cause the combustion to burn very rapidly and hot, while having lots of fuel, but no air will cause the mixture to burn very cool and slowly. Having an overly gross amount of either fuel or air will cause the combustion to not even occur at all.

What is Lambda?

Lambda is scale that relates the air to fuel ratio of ANY fuel. 1.0 is stoic for every fuel. (the chemically perfect ratio of air to fuel for a complete burn). However, stoic is different for every fuel. Some fuels may need 14.7 lbs of air some may need 6 lbs of air for a complete burn. Lambda 1.0 is always the perfect ratio for the fuel in use.

Some tuners argue that it is better to read air to fuel ratio’s in lambda since it will be accurate with any fuel. To be fair though, most aftermarket gauges will read lambda and convert that number to an a/f ratio for gasoline. If the user then knows the stoic, lean, and rich ratio’s for gasoline, he can apply those numbers to any fuel used and it won’t matter.

What I mean is that if you are running 14.7 (stoic) on a gasoline A/F gauge and you then convert to alcohol ( or E85 ), 14.7 will still be stoic on the gasoline gauge. This is because the gauge is going to read a stoic lambda reading of 1.0 for any fuel, and the gauge is going to output that number as 14.7 on you’re A/F gauge even though we know the true ratio for alcohol is 7.1-9.1.

Many times I have then seen people try and richen the cars tuning map to get down to that A/F value, not realizing that they are already at a stoic burn if the gauge set up for gasoline reads 14.7.

 

Interesting...

 

Yea this is everyone is scared to make the switch to lambda when in all reality, it is so much easier than having to worry about stoich your fuel is running at. Everyone gets confused when stoich is thrown in the mix.

Set you **** up in lambda and never look back.

 

I wish my display used lambda.

But I'm also fine with the gas AFR scale for E85.

 

so when using the gas AFR scale for e85 with a lambda wideband do you still target 14.7 and high 11's in boost?

 

Yes. All the gauge is doing is taking lambda and converting that number to whatever scale you set it up to use.

 

I ask because I was told even with my lambda LC-1 gauge that is set up to read gasoline stoichiometry that when spraying meth I should target 10.8.

 

Meth doesn't have the same stoich value as gasoline. This is why it is so difficult. When you start mixing fuels like pump gas and meth, you don't really know what to target. Pump gas has up to 10% ethanol in it which also has a different stoich than methanol and gasoline. So now you have to find an average stoich between all three fuels. Headache yet?

 

Obviously when you're spraying meth, you aren't targeting stoich so you'll have to know on the methanol scale where that fuel makes best power or prevents detonation the best. Then do the same with E10 and find the best value to target on the gasoline scale. You will also have to take into consideration how much of each fuel you are spraying. So your final value should be skewed toward the E10 since you will most likely be spraying more of it.

 

Thats where I was and still am slightly confused... if the sensor just reads lambda then does it even matter what you're burning? Its just converting it to the gasoline scale of 14.7 on my gauge, but I fail to see how when running e85 it would be different than spraying meth (outside of the actual fuel being very different) when reading the gauge. I understand that the target AFR is drastically different, but using a lambda meter thatgives you a somewhat arbitraty reading that doesnt matter? Or am I missing the point?

For instance I'm burning e10 in MA. Is it safe to assume that since my wideband reads lambda and i have it programmed on the gasoline scale that when it reads 14.7 I'm actually running a 14.0 AFR? btw 14 is somewhat of an estimate on my part.