what to believe...A/F

Joined
Jul 26, 2005
Messages
522
Location
Fort Myers, Florida
I'm trying to figure out what my A/F is. I had the car on the dyno with their "sniffer" and got a fairly even 12.5 throughout the rpm range. On the street with my wideband UEGO controller I'm seeing numbers in the mid-high 11's and based on the rear valence discoloration, the car seems rich. What should give the most accurate reading?
 
Joined
Jun 2, 2006
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Mark I am not sure but if you had Cats...and the sniffer was after...it may affect reading?
 
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Sep 28, 2004
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1,743
just me, but i would be going by the wideband,
just a ????? if you have a wideband, why would they tune with the sniffer and not put the 02 sensor in the bung? do you have the AEM ecu also?
 
Joined
Jul 26, 2005
Messages
522
Location
Fort Myers, Florida
just me, but i would be going by the wideband,
just a ????? if you have a wideband, why would they tune with the sniffer and not put the 02 sensor in the bung? do you have the AEM ecu also?


No cats...wideband seems right based on the dirty rear valance - although that could be because the cats are gone as well. Tuner felt more comfortable with the sniffer - based on using it for most everything he tunes.The wideband seems to mirror the sniffer throughout the rpm range - it's just that it show A/Fs in the 11's vs 12's
 
Joined
Nov 6, 2006
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Location
Austin, TX
My 2cents..

I also have a wideband, took it to one tuner, and they screwed it up by using the wideband.

Took it to another tuner that just used the sniffer and it runs solid now. He said he's found the wideband to be off sometimes and he doesn't trust it as too much. I'll give him the benefit of the doubt since it's been 15K+ and the car hasn't blown up.
 
Joined
Apr 13, 2008
Messages
11
sorry, but there is no 'magic' a/f ratio. check out one of efi101.com's newsletters. there's even a government paper on it from ww2 fighter planes. not that we can trust them today but back then they had superchargers on v-16 planes to kick some ass.

i have found many aftermarket widebands to be off vs the high dollar units like a motec plm that is properly calibrated.

the aem is perhaps the worst. very good from 12.5 up, but under that it will read as much as a point lower than a plm. innovate is a bit better and ntk sensor with plx is better.

but plm is $1500.

go to dyno though (that uses plm, all dynapacks do) and you'll see 11.5 will likely make within 2% of 12:1. probably same for 11:1 vs 12:1 on boosted engine.

engines DO have high and low bands where they're comfortable, but it's much wider than you'd think. ignition timing is MUCH more critical.

looks like slown's guy understands this based on his personal experience.

placement can be critical too, though there is not that much of a difference between before cat and after cat. tested it and never seen more than .5 higher or lower with a properly functioning cat (this includes flow as that will DRASTICALLY affect results).

i believe, tune until power goes down statistically and then cut back (leaner) .5 (half) a/f ratio.
 
Joined
Apr 5, 2005
Messages
220
Does your tuner have a long history of reliable tunes, good economy, and drivability with the A/F readings from their equipment? If your tuner always uses one brand/type of wideband and one method of placement for measuring air/fuel, let your tuner continue to use his preferred device and technique. If your relationship with the tuner is brand new and you feel the results are less than perfect, ask around for feedback from other enthusiasts and change tuners.

Here is some interesting information regarding AEM wideband accuracy:

Several major automakers have used AEM wideband units during engine, performance part, and racing development programs. Mopar Performance engineers for instance, used AEM widebands during the development of their 5.7L Hemi, 6.1L Hemi, and 392 Hemi crate engine.

Last year, a Chrysler engineer responsible for some 6.1L Hemi long-term durability testing reported back to us about some really interesting data. During a 200 hour long durability test, a pair of our inexpensive little AEM wideband sensors were mounted in the same collectors as a pair of laboratory-grade $5,000 Horiba controller sensors. He found that the logged readings from each brand fell within one to two tenths of each other throughout the range of the test (10.5:1 A/F gasoline to 15.5:1 A/F gasoline).
 
Joined
Sep 22, 2005
Messages
1,216
Does your tuner have a long history of reliable tunes, good economy, and drivability with the A/F readings from their equipment? If your tuner always uses one brand/type of wideband and one method of placement for measuring air/fuel, let your tuner continue to use his preferred device and technique. If your relationship with the tuner is brand new and you feel the results are less than perfect, ask around for feedback from other enthusiasts and change tuners.

Here is some interesting information regarding AEM wideband accuracy:

Several major automakers have used AEM wideband units during engine, performance part, and racing development programs. Mopar Performance engineers for instance, used AEM widebands during the development of their 5.7L Hemi, 6.1L Hemi, and 392 Hemi crate engine.

Last year, a Chrysler engineer responsible for some 6.1L Hemi long-term durability testing reported back to us about some really interesting data. During a 200 hour long durability test, a pair of our inexpensive little AEM wideband sensors were mounted in the same collectors as a pair of laboratory-grade $5,000 Horiba controller sensors. He found that the logged readings from each brand fell within one to two tenths of each other throughout the range of the test (10.5:1 A/F gasoline to 15.5:1 A/F gasoline).

I 100% believe this statement. I have seen many AEM widebands be dead on with the tuning equipment most dyno shops use.
 
Joined
Jul 26, 2005
Messages
522
Location
Fort Myers, Florida
Ok, my next question is...if the wideband units are as accurate as you say, do you see any reason why I can't try out my smaller CTSC pulley (adds about 2-3 more PSI) and use the widebands and AEM data logger to check that I'm within safe readings.

Does your tuner have a long history of reliable tunes, good economy, and drivability with the A/F readings from their equipment? If your tuner always uses one brand/type of wideband and one method of placement for measuring air/fuel, let your tuner continue to use his preferred device and technique. If your relationship with the tuner is brand new and you feel the results are less than perfect, ask around for feedback from other enthusiasts and change tuners.

Here is some interesting information regarding AEM wideband accuracy:

Several major automakers have used AEM wideband units during engine, performance part, and racing development programs. Mopar Performance engineers for instance, used AEM widebands during the development of their 5.7L Hemi, 6.1L Hemi, and 392 Hemi crate engine.

Last year, a Chrysler engineer responsible for some 6.1L Hemi long-term durability testing reported back to us about some really interesting data. During a 200 hour long durability test, a pair of our inexpensive little AEM wideband sensors were mounted in the same collectors as a pair of laboratory-grade $5,000 Horiba controller sensors. He found that the logged readings from each brand fell within one to two tenths of each other throughout the range of the test (10.5:1 A/F gasoline to 15.5:1 A/F gasoline).
 
Joined
Apr 5, 2005
Messages
220
I don't think any of us should tell you what to do with your boost levels or how to tune your car. There are way too many variables that come into play here and air/fuel is just one small piece of the equation.

Hopefully you can put your faith in a local tuner that can help you decide what is best for your particular setup.
 
Joined
Jul 26, 2005
Messages
522
Location
Fort Myers, Florida
I don't think any of us should tell you what to do with your boost levels or how to tune your car. There are way too many variables that come into play here and air/fuel is just one small piece of the equation.

Hopefully you can put your faith in a local tuner that can help you decide what is best for your particular setup.

10/4...back to the tuner.
 
Joined
Nov 23, 2006
Messages
104
As a point of interest, we use AEM widebands on every car we build at our shop and test every single unit out against Our dyno wideband to make sure the units are reading correct. We have installed over 50 of these units recently and found only one to be reading off (.5 lean at 11.0afr). The service life of the sensors on race gas is alittle short however if your burning race gas a 70.00 sensor every 4-6 months shouldnt be a concern.
 
Joined
Apr 14, 2008
Messages
1
Something else to consider is tha there is a different amount of load on the dyno vs on the street. On the dyno there is generally a lot less load placed on the car. I found this out when I put my car on the dyno and it was making less boost than on the street. This is because the dynojet does not simulate as much load as the street does. Perhaps your car is just running richer because there is more load on the street.
 
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