A/F GUIDE

[RyanM]

Thought it was a good read and was worth a thread http://www.svtsnake.com/forum/showthread.php?t=2075

[RyanM]

I would like to hear some of the opinions from tuners on this board and what they think about it

[EFI Performance]

Nice Link A+

Here's some info off it...

The A/F sensor is the most important device used when tuning. Unfortunately, I've seen many DynoShops use equipment that is too old, and too low of quality and they don't realize it.

So here is what happens way too often.

You go to your local dyno. They don't replace the sensor that often since it still gives a reading. In their minds, if the signal is moving around, showing a changing A/F ratio, the data is good. This could not be farther from the truth. If their cheap sensor is more than a few months old, I can assure you that the A/F ratio coming from the sensor is NOT accurate. So, they tune your car, it's lean. They add fuel and take you aside and tell you how good it is that they richened it up before it did any damage. So you leave feeling good that your car is now safe. But in reality, it's way too rich. It is safe, but you are 1.0 A/F richer than you should be. So, you just left some power on the table and wonder why it's soo rich when it was good on the dyno.

Now you go to a different dyno and get a different A/F reading, big surprise. Which is right? I have no idea. Chances are they are both wrong.

My understanding is that dyno jet's can only load a car to about 2200 pounds so the car is never under real load conditions like driving on the street when on a dynojet. That why lots of tuners like to use the mustang dyno or superflow dynos.

[OffShore]

my vette was spot on w my lm-1 on the dyno and wi .3 on he street

[EFI Performance]

My AEM WB was within .1 AFR with a DynaPack's WB, both sensors were new out of the box that day.

I dialed my cars AFR at 12.0;1 on the dyno. Then I ran it down the track and it was lean on the top end, under full boost. (I just corrected it at the track. no big deal!)

[Southern]

Good info Ryan. I read all of it.

[I Tried]

Good read Ryan. Did you get your car on the Dyno yesterday????

[RyanM]

Good read Ryan. Did you get your car on the Dyno yesterday????

no im waiting on a IAC motor from the backfire at the track, should be here today

[Sweet35th]

My AEM WB was within .1 AFR with a DynaPack's WB, both sensors were new out of the box that day.

I dialed my cars AFR at 12.0;1 on the dyno. Then I ran it down the track and it was lean on the top end, under full boost. (I just corrected it at the track. no big deal!)

Good info, along with the link you posted above.

I would argue with that individual who stated that O2s a month old are no longer in calibration (in the quote you posted from that link), and you could be leaving excessively rich. Its very easy to moniter A/F while a vehicle is in closed loop, and that is a very acurate time to check and see how an O2 is reading. If I have a vehicle in closed loop, and moniterd the wideband and see its reading 16.0:1 even under light load (still closed loop) then I know that wideband is faulty. But if its reading properly at 14.5-15.0:1 and I can moniter the factory O2s and LTFT/STFTs and they agree with the wideband reading. Most widebands produce a linear voltage from 10:1 to 15:1. This means that the O2 is no more sensitive at 10:1 than it is at 15:1. They start to be come less sensitive beyond 15:1. What this means, is if your wide band is reading acuratly at 14.5:1, then it is in all likelyness reading acurately at 12.0:1.

EFIperformance. You took two sensors new out of box, and they were within .1 of eachother, so they were pretty damn accurate I would say. Where they both in the same location?

The only reason I ask, is because I have found that the location of the O2 sensor is far more critical in CONSISTANCY, than the differance between two differant O2s, even between a new O2, and one a few months old..

In my experiance, the closer an O2 gets to the cylinder head, the more sensitive it becomes. You start getting readings caused by exhaust scavaging, light missfires, ect. Its not so much that the O2 reads drasticaly differant than it does further downstream, but rather less smooth in its reading...If you were to graph it out, you would see the not so perfectly smooth line you may be used to seeing when a/f is measure in the tail pipe. To continue on that, it has also been in my experiance that the O2 in the tail pipe typicaly reads .2-.3 LEANER than the O2 being mounted upstream..

Too many people focus themselfs on what MUST be the right A/F ratio. When the truth of the matter is, that there are too many variables that can effect A/F one way or another. Differant brands of O2s, differant brands of gauges, and even the placement of the O2. You have to use what you know is SAFE, and work from there.

You know that far a supercharged vehicle 11:1 is safe. So start there, and start pulling fuel out .5 at a time. If you get to 12:1, and power only picked up a few horse, richen it back up.. If you get to 12.0:1 and the thing is up 30hp, check your plugs and see how they are burning, if they look like they are too lean, then back if off again. If they look good then let'r buck.

You will gain experiance with the wideband you use, and how it relates to how a vehicle is running....These realy ARE NOT precision measuring tools, and people have to remember that. You work with them off of what is know, and work for consistancy....

I know, based on the experiance that I have with my wideband, weather it in the tail pipe or up by the header, on an 03 Cobra for example, that I will find little or no power leaning it out from 11.8:1 to 12.2:1, so why run the risk of running it leaner. And if I only gained 2hp from leaning it out from 11.5:1 to 11.8:1, then I am going to put it back to 11.5:1. Because just as Russ pointed out, sometimes despite being perfect on the dyno, it may be slighly off on the track, and its always to error on the safe side.

[wiplash]

There's some misinformation on there, "isdnmatt"s post is WAY off when he explains load and how load tables should be setup. I'm seeing 1.9 load at 8lb's, according to him I don't need anymore than 1.5 to poperly tune a car seeing less than 10lb's.

[Video_Master]

I like your post Casey and I remember when I was in their last spring that this is what you did with my car. It was very interesting to watch what you did and you showed me the differece from my DJWBC and your WB on the Dyno and the difference was that .3 which made alot of sense becuase of where my WB O2 is located. I love reading things like this cause it is very educational and great to get opinions from different tuners to see how they deal with things.

[LES]

Good info, along with the link you posted above.

I would argue with that individual who stated that O2s a month old are no longer in calibration (in the quote you posted from that link), and you could be leaving excessively rich. Its very easy to moniter A/F while a vehicle is in closed loop, and that is a very acurate time to check and see how an O2 is reading. If I have a vehicle in closed loop, and moniterd the wideband and see its reading 16.0:1 even under light load (still closed loop) then I know that wideband is faulty. But if its reading properly at 14.5-15.0:1 and I can moniter the factory O2s and LTFT/STFTs and they agree with the wideband reading. Most widebands produce a linear voltage from 10:1 to 15:1. This means that the O2 is no more sensitive at 10:1 than it is at 15:1. They start to be come less sensitive beyond 15:1. What this means, is if your wide band is reading acuratly at 14.5:1, then it is in all likelyness reading acurately at 12.0:1.

EFIperformance. You took two sensors new out of box, and they were within .1 of eachother, so they were pretty damn accurate I would say. Where they both in the same location?

The only reason I ask, is because I have found that the location of the O2 sensor is far more critical in CONSISTANCY, than the differance between two differant O2s, even between a new O2, and one a few months old..

In my experiance, the closer an O2 gets to the cylinder head, the more sensitive it becomes. You start getting readings caused by exhaust scavaging, light missfires, ect. Its not so much that the O2 reads drasticaly differant than it does further downstream, but rather less smooth in its reading...If you were to graph it out, you would see the not so perfectly smooth line you may be used to seeing when a/f is measure in the tail pipe. To continue on that, it has also been in my experiance that the O2 in the tail pipe typicaly reads .2-.3 LEANER than the O2 being mounted upstream..

Too many people focus themselfs on what MUST be the right A/F ratio. When the truth of the matter is, that there are too many variables that can effect A/F one way or another. Differant brands of O2s, differant brands of gauges, and even the placement of the O2. You have to use what you know is SAFE, and work from there.

You know that far a supercharged vehicle 11:1 is safe. So start there, and start pulling fuel out .5 at a time. If you get to 12:1, and power only picked up a few horse, richen it back up.. If you get to 12.0:1 and the thing is up 30hp, check your plugs and see how they are burning, if they look like they are too lean, then back if off again. If they look good then let'r buck.
You will gain experiance with the wideband you use, and how it relates to how a vehicle is running....These realy ARE NOT precision measuring tools, and people have to remember that. You work with them off of what is know, and work for consistancy....

I know, based on the experiance that I have with my wideband, weather it in the tail pipe or up by the header, on an 03 Cobra for example, that I will find little or no power leaning it out from 11.8:1 to 12.2:1, so why run the risk of running it leaner. And if I only gained 2hp from leaning it out from 11.5:1 to 11.8:1, then I am going to put it back to 11.5:1. Because just as Russ pointed out, sometimes despite being perfect on the dyno, it may be slighly off on the track, and its always to error on the safe side.

Agreed, I was so worried about AFR when EFI first tuned my car I was constantly watching it. My car as I drove it , and with differant gas ran at differant AFR. EFI had a Dead on 11.8 when I picked the car up. When we put good gas in it at the track it when to 10.0 . I decreased fuel and it came back around to High 11'S. When I went back to pump gas I was seeing 12.0-12.5 and worried. EFI would say " do you hear detonation?" I never heard detonation one time so I just quit thinking about it and let it buck. 12.0-12.5 on 12# of boost and pump gas. I also remember his saying something about it pegging the virtual load meter on the TWEECER. I think every car is differant and you should tune to a AFR base then tweak from there like Casey said. When I went to the smaller pulley at CFR and saw 15# of boost, I saw 13.0 plus AFR on my last run, car went as fast as it ever has. When I tore motor down, 0 signs of detonation and or issues. Pistons and valves had great color and like new surface.

[EFI Performance]

I would argue with that individual who stated that O2s a month old are no longer in calibration (in the quote you posted from that link), and you could be leaving excessively rich. Its very easy to moniter A/F while a vehicle is in closed loop, and that is a very acurate time to check and see how an O2 is reading. If I have a vehicle in closed loop, and moniterd the wideband and see its reading 16.0:1 even under light load (still closed loop) then I know that wideband is faulty. But if its reading properly at 14.5-15.0:1 and I can moniter the factory O2s and LTFT/STFTs and they agree with the wideband reading. Most widebands produce a linear voltage from 10:1 to 15:1. This means that the O2 is no more sensitive at 10:1 than it is at 15:1. They start to be come less sensitive beyond 15:1. What this means, is if your wide band is reading acuratly at 14.5:1, then it is in all likelyness reading acurately at 12.0:1.

Good point Casey! On how to make sure your wideband is working proper!

EFIperformance. You took two sensors new out of box, and they were within .1 of eachother, so they were pretty damn accurate I would say. Where they both in the same location?

The only reason I ask, is because I have found that the location of the O2 sensor is far more critical in CONSISTANCY, than the differance between two differant O2s, even between a new O2, and one a few months old..

I have shorty headers with 2 bungs on each side at the exact same distance down the pipe. The factory O2's were being used and the EFI was in closed loop, so the left and right bank were reading identically the same AFR.

You know that far a supercharged vehicle 11:1 is safe. So start there, and start pulling fuel out .5 at a time. If you get to 12:1, and power only picked up a few horse, richen it back up.. If you get to 12.0:1 and the thing is up 30hp, check your plugs and see how they are burning, if they look like they are too lean, then back if off again. If they look good then let'r buck.

You will gain experiance with the wideband you use, and how it relates to how a vehicle is running....These realy ARE NOT precision measuring tools, and people have to remember that. You work with them off of what is know, and work for consistancy....

I know, based on the experiance that I have with my wideband, weather it in the tail pipe or up by the header, on an 03 Cobra for example, that I will find little or no power leaning it out from 11.8:1 to 12.2:1, so why run the risk of running it leaner. And if I only gained 2hp from leaning it out from 11.5:1 to 11.8:1, then I am going to put it back to 11.5:1. Because just as Russ pointed out, sometimes despite being perfect on the dyno, it may be slighly off on the track, and its always to error on the safe side..

Good Points. It gets intreasting how different climate changes can effect the way vehicles run and perform.
For most street cars I leave the AFR on the error of the rich side and the timing on the low side. But for racing applications, I look for the most HP and Torks.

Casey, How often do you need to change the wideband sensor on the dyno? Just a estimated life expecetancy of a shops sensor...

And also how much of a change do you see in the AFR readings before the cat convertor, compare to behind the cat convertors?

Russ

[EFI Performance]

There's some misinformation on there, "isdnmatt"s post is WAY off when he explains load and how load tables should be setup. I'm seeing 1.9 load at 8lb's, according to him I don't need anymore than 1.5 to poperly tune a car seeing less than 10lb's.

I think the differences between your car and his could be the PCM stragy. (His might be a cobra and yours a GT?) I think you can change scalers, (depending on application) that can lower or raise the inferred load values, without changing anything on the engine.

I did it on my ProCharged 99 GT because I was always pegging the load values off the table.

Russ

[Sweet35th]

Casey, How often do you need to change the wideband sensor on the dyno? Just a estimated life expecetancy of a shops sensor...

And also how much of a change do you see in the AFR readings before the cat convertor, compare to behind the cat convertors?

Russ, I have no set time that I replace the sensor, cause I think its lifespan is more effected by contamination that time frame......Get alot of leaded fuel vehicles, and I have to replace it more often, than a bunch of N/A cars running at 13:1. The same goes for forced induction vehicles, if I get a string of cars running 11-12:1 it seems to plug up the sensor faster..

I like to have 2 sensors at all times. One new, and then the one that is in continue use. This way if one of my sensors starts reading odd, I can swap in the other one. If the A/F changes drasticaly, then I know its time to rotate my stock so to speak. If the A/F is still odd, then I know I have to start looking elsewhere for issues.

As far as before or after the cat, I have never done a real controlled test, but would be interesting to do so. The .2-.3 leaner in the tail pipe seems to be consistant weather the car has cats or not, so I would have to believe that if A/F were measured in a bung right after the cat, it would be fairly close to what it is before the cat.......But would make an interesting experiment to try it at a variety of a/f ratios while trying to eliminate any variables.. I guess I have never worried about it too much, becuase if I get a vehicle (say a KB blown 03-04 cobra, or a blown 2V gt with a stock bottom end), that had cats and was concerned about the A/F being effected by the cats, I always measure upstream of them....

Some saturday when things are slow, I think it will take 2 O2s (one brand new, and one that say has 20 cars ran on it), on a vehicle that has a consistant A/F with cats and measure it with both O2, and check it at all differant locations to see the differance in measure from both O2s at every possible locations.