AFR vs Lambda... why ever use AFR?
AFR vs Lambda... why ever use AFR? I am curious why anyone would use AFR to tune when most pump gas has some percentage of ethanol and additives in it, which changes the Stoich.
Force of habit? Kidding but not kidding. I learned on lambda, and it's far easier to convert for various fuels. You can never completely divorce AFR, because at some point you have to tell the computer how much fuel to squirt for the air it ingested. But for logging, etc, the first thing I do is take everyone's transforms and convert to lambda
AFR is imperial and Lambda is metric system and people hate the metric system.
People have used AFR for years because pump gas was well...actually gas. It's not anymore.
A lot of PCM's are written in AFR, well GM's are anyway. The PCM in my 2000 T/A is in AFR, and I have to reverse engineer the multipliers to get the commanded Lambda I want. I had a spreadsheet a long time ago that I made but I can't find it anymore.
What's the stoich of E15, or E30, what about E50? I don't know..but I can tell you in Lambda all of them are 1.0
People have used AFR for years because pump gas was well...actually gas. It's not anymore.
A lot of PCM's are written in AFR, well GM's are anyway. The PCM in my 2000 T/A is in AFR, and I have to reverse engineer the multipliers to get the commanded Lambda I want. I had a spreadsheet a long time ago that I made but I can't find it anymore.
What's the stoich of E15, or E30, what about E50? I don't know..but I can tell you in Lambda all of them are 1.0
TECH Fanatic
Joined: Oct 2014
Posts: 1,220
Likes: 179
From: Virginia
Either is fine really, as long as you have the correct stoich set as the target. For example E10 should be down in the 14.1 ish range, since the E10 is really E10 ish anyway. That would also matter for lambda too. Lambda is simply a reference to your target, so 1.0 is whatever stoich is set to. I could make it 18:1 and tune it, it would say 1.0, and I’d be wrong as hell. AFR is the actual you’re seeing in real time. For gas motors and average joes, AFR is just easier to explain because there are no “extra steps”…
A wideband is a Lambda sensor. Not an AFR sensor.
we've been asking Holley for years to have a Lambda option. They said they were going to put it in back when V4 released.
we've been asking Holley for years to have a Lambda option. They said they were going to put it in back when V4 released.
Trending Topics
Originally Posted by theunderlord
I've watched countless Joe Simpson Holley tuning videos where he begs for a straight Lambda set up from Holley.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
"AFR" is just an old habit from pure-gasoline era. People who speak in terms of AFR (myself included) are actually talking about lambda, just in different units of measurement. The ratio of fuel mass to air mass in the combustion chamber won't exactly match the spoken/written AFR, but it will match the lambda that corresponds to the spoken/written AFR for whatever the fuel happens to be.
The sensors in the vehicle measure lambda, regardless of fuel, and the conversion is trivial, so this ends up being just a distinction without a difference.
The sensors in the vehicle measure lambda, regardless of fuel, and the conversion is trivial, so this ends up being just a distinction without a difference.
Yeah they are too busy trying to get a 6spd transmission to work, rather than provide that kinda stuff. I guess they figure if we are using their products we can figure it out. While we can, I agree, it sure would be nice if it would just identify it. The crank sensor is already there, they just need to write a little code.
TECH Fanatic
Joined: Oct 2014
Posts: 1,220
Likes: 179
From: Virginia
Technically, AFR and Lambda are the same thing, just different units. It’s literally like comparing gallons to liters. One is in percentage of stoich (lambda) and one is raw ratio (AFR)… it literally doesn’t matter which you use so long as you have the base (target) set appropriately for the fuel type. That’s my take on it at least. No matter what, lambda is still a ratio of air to fuel, and AFR, well, literally the ratio of air to fuel. Lambda is definitely easier to use for different fuels because you don’t have to be a math whiz to know when you’re off target. But at the end of the day, both still measure the same thing.
TECH Fanatic
Joined: Oct 2014
Posts: 1,220
Likes: 179
From: Virginia
Since no matter what, my REAL reference is literally the oxygen left in the pipe after combustion (or lack thereof) then the argument over which “ratio” works better is moot. Both work. Be it lambda, or AFR, both measure this ratio. It’s like saying I’m wrong for saying 1 inch when you’re saying 25.4mm. We’re saying the same thing. You just have to know your numbers better if you use AFR. I suppose that can actually be more difficult with other fuels. 1.0 lambda is whatever I tell the PCM 1.0 is on the stoich table.
I just don’t see how wideband O2 sensors are “lambda” sensors. Maybe stock ones. Maybe I’m completely wrong, so enlighten me if I’m way off track here. As I understand it, lambda is 1.0 at whatever I set stoich to. That means it’s also “x” AFR at the same stoich value. What is the difference if one chooses to see 1.0 or “x” AFR value? I don’t see the issue, or a difference. It’s literally just a different unit.
I think the Holley ECM reads in Lambda and then they do an extra step in the software to convert to AFR. It's kind of silly they don't have an option to tune in Lambda. Just makes things more awkward when they don't. Estimating fueling changes when tuning in Lambda is so easy that you can do the math in your head.
TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
I’m not quite following what you’re saying here. A wideband is simply an O2 sensor with greater range (5v) than the stock ones (1.2v). They operate based on the difference of outside air vs inside air. The greater the difference (or lack thereof of oxygen aka O2) the greater the voltage produced. The materials used to make O2 sensors actually create voltage in this scenario, just like little generators. The ratio I’m looking for in the tune is up to whatever my sensor bandwidth is.
In order to turn lambda into AFR something has to do a little arithmetic based on how many grams of air can be burned by a gram of the particular fuel in question (i.e. the stoichiometric ratio of that fuel). The O2 sensor doesn't know what kind of fuel went into the other end of the motor, so the sensor just has lambda.
Last edited by NSFW; Feb 26, 2022 at 01:19 PM.
AFR is imperial and Lambda is metric system and people hate the metric system.
People have used AFR for years because pump gas was well...actually gas. It's not anymore.
A lot of PCM's are written in AFR, well GM's are anyway. The PCM in my 2000 T/A is in AFR, and I have to reverse engineer the multipliers to get the commanded Lambda I want. I had a spreadsheet a long time ago that I made but I can't find it anymore.
What's the stoich of E15, or E30, what about E50? I don't know..but I can tell you in Lambda all of them are 1.0
People have used AFR for years because pump gas was well...actually gas. It's not anymore.
A lot of PCM's are written in AFR, well GM's are anyway. The PCM in my 2000 T/A is in AFR, and I have to reverse engineer the multipliers to get the commanded Lambda I want. I had a spreadsheet a long time ago that I made but I can't find it anymore.
What's the stoich of E15, or E30, what about E50? I don't know..but I can tell you in Lambda all of them are 1.0
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
If you go way way back,, Airplanes had a AFR table in the manual to assist in properly adjusting the mixture, So a ton of early engine guys were ex military who got in to racing.. So they used what they knew. It assisted with fuel burn calcs as well.
Haven't seen one in years..
Haven't seen one in years..