Edelbrock's Air/Fuel Ratio Table from 1993
July 23rd, 2019, 10:05 AM
#1
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Edelbrock's Air/Fuel Ratio Table from 1993
I was looking over my book collection this morning and about to toss a 1993 vintage EFI book, when I cracked it just to see how out of date it might have become. The book is call "Fuel Injection" by Jeff Hartman in the Motorbooks International Powerpro Series.
Some of you may know I added wideband Air/Fuel Ratio guages on my cars in an attempt to get better starting, better running cars, and maybe improve power & economy. That's been working fairly well, but I haven't been able to find AFR parameters to aim at while tuning. Today I ran across this table published by Edelbrock for their (now very old) systems. I can't confirm it's accuracy or correctness, but the figures looked reasonable enough for me to want to pass along to you all in case you're working on EFI systems or have and AFR gauge like me.
Air-Fuel Ratio Mixtures & Characteristics
Mixture Rating Comment
6.0 Rich burn limit (fully warm engine)
9.0 Black smoke, low power
11.5 Approximate rich best torque at wide open throttle
12.2 Safe best power at wide open throttle
13.3 Approximate lean best torque
14.6 Stoichiometric air-fuel ration (chemically ideal)
15.5 Lean cruise
16.5 Usual best economy
18.0 Approximate rich best torque at Wide Open Throttle
22+ EEC and EFI lean burn limit
I claim no expertise here. Perhaps Joe and CutlassEFI have better information, but I hope this table helps some of you
Cheers,
Chris
Some of you may know I added wideband Air/Fuel Ratio guages on my cars in an attempt to get better starting, better running cars, and maybe improve power & economy. That's been working fairly well, but I haven't been able to find AFR parameters to aim at while tuning. Today I ran across this table published by Edelbrock for their (now very old) systems. I can't confirm it's accuracy or correctness, but the figures looked reasonable enough for me to want to pass along to you all in case you're working on EFI systems or have and AFR gauge like me.
Air-Fuel Ratio Mixtures & Characteristics
Mixture Rating Comment
6.0 Rich burn limit (fully warm engine)
9.0 Black smoke, low power
11.5 Approximate rich best torque at wide open throttle
12.2 Safe best power at wide open throttle
13.3 Approximate lean best torque
14.6 Stoichiometric air-fuel ration (chemically ideal)
15.5 Lean cruise
16.5 Usual best economy
18.0 Approximate rich best torque at Wide Open Throttle
22+ EEC and EFI lean burn limit
I claim no expertise here. Perhaps Joe and CutlassEFI have better information, but I hope this table helps some of you
Cheers,
Chris
July 23rd, 2019, 11:36 AM
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I don't usually reply to my own posts, but just wanted to add that the stoichiometric ratio for fuel with an alcohol component is somewhat richer.
To compensate for the lower fuel potential of alcohol I'd adjust the numbers above down (richer) by .3 or so. Meaning instead of pure gasoline target of 14.6:1, the gas-with-alcohol target would be more 14.3:1.
Again, anyone with deeper knowledge please jump in. In my mind these are rough estimates but I'm hoping they're directionally correct.
I was just pleased to finally have some goals to shoot for in quadrajet tuning instead of shooting in the dark with each tweak.
Chris
To compensate for the lower fuel potential of alcohol I'd adjust the numbers above down (richer) by .3 or so. Meaning instead of pure gasoline target of 14.6:1, the gas-with-alcohol target would be more 14.3:1.
Again, anyone with deeper knowledge please jump in. In my mind these are rough estimates but I'm hoping they're directionally correct.
I was just pleased to finally have some goals to shoot for in quadrajet tuning instead of shooting in the dark with each tweak.
Chris
July 23rd, 2019, 05:40 PM
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Location: Central Fl
Posts: 7,892
Stoich with E10 is now 14.1:1. I seem to get best power at 12.2-12.5:1 typically. Cruise can be in high 13’s all the way to high 14’s ish depending on camshaft and the amount of vacuum advance.
Hope this helps and kudos for buying a wideband👍.
Hope this helps and kudos for buying a wideband👍.
Last edited by cutlassefi; July 23rd, 2019 at 05:42 PM.
July 24th, 2019, 07:39 AM
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Location: Pittsburgh, PA
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Keep in mind the Stoichiometric numbers are calculated for the type of fuel, but if you are reading a wide band (that is calibrated for gasoline), it does not know the fuel type, so a stoichiometric tune still shows 14.6 even though you may be running say 14.3 on E10.
I have also tested pump fuels & I see about 8% in the current E10 in my area.
The wide band only reads the oxygen percentage so stoichiometric is stoichiometric or some factor above/below. You need to set the stoich value in you wideband to match the fuel type.
Most people running wide bands on other fuels set the wide band to display in lambda so stoich is 1.0 & you calculate the rich/lean percentage up or down accordingly... a 0.9 value is (.9*14.6 on gas=13.15, or E85 .9*9.8=8.82 for example)
In summary, if you do not reset the stoic value on your wide band to match your fuel (you don't have to), assume 14.6 is stoich for cruise & mid to upper 12's is a reasonable value for WOT tuning.
Also I have found the latest EFI engines like to be lean. My LS3 makes best power at 13-13.1, whereas the Carbed 396 in my 68 Camaro is happiest at 12.7.
I have also tested pump fuels & I see about 8% in the current E10 in my area.
The wide band only reads the oxygen percentage so stoichiometric is stoichiometric or some factor above/below. You need to set the stoich value in you wideband to match the fuel type.
Most people running wide bands on other fuels set the wide band to display in lambda so stoich is 1.0 & you calculate the rich/lean percentage up or down accordingly... a 0.9 value is (.9*14.6 on gas=13.15, or E85 .9*9.8=8.82 for example)
In summary, if you do not reset the stoic value on your wide band to match your fuel (you don't have to), assume 14.6 is stoich for cruise & mid to upper 12's is a reasonable value for WOT tuning.
Also I have found the latest EFI engines like to be lean. My LS3 makes best power at 13-13.1, whereas the Carbed 396 in my 68 Camaro is happiest at 12.7.
Last edited by Lonnies Performance; July 24th, 2019 at 07:43 AM.
July 24th, 2019, 11:07 AM
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Location: Central Fl
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If the gauge is reading 14.1 then it’s 14.1. Stoich can only be changed if the Gauge/wideband allows. Not all do. Just stick with the values I gave and you should be fine.
And EFI in itself seldom effects what’s best for WOT. That LS3 likes it leaner because that engine was designed from a clean sheet of paper specifically for EFI. Please don’t compare that to the 50 year old iron the rest of us work on.
And EFI in itself seldom effects what’s best for WOT. That LS3 likes it leaner because that engine was designed from a clean sheet of paper specifically for EFI. Please don’t compare that to the 50 year old iron the rest of us work on.
July 24th, 2019, 11:41 AM
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Only if you change the stoic value to match the fuel in use. If running E10 & it was calibrated for straight gasoline then the the 14.1 displayed is no longer correct.
The gauge is reading the lambda (oxygen) value & multiplying it by the stoic value to display this air fuel ratio number.
My point was If you cant change the stoic values on the sensor, then it is only accurate on what fuel the gauge is calibrated for... It does not know the fuel in use & does not measure air/fuel ratios, it measures oxygen content.
For example, I have used wide bands on methanol fueled cars & it reads the gasoline values which are roughly double the actual if you do not reset the stoic value.
The car would not even run at the values displayed on the sensor, proving it is not reading the air/fuel ratio.
The gauge is reading the lambda (oxygen) value & multiplying it by the stoic value to display this air fuel ratio number.
My point was If you cant change the stoic values on the sensor, then it is only accurate on what fuel the gauge is calibrated for... It does not know the fuel in use & does not measure air/fuel ratios, it measures oxygen content.
For example, I have used wide bands on methanol fueled cars & it reads the gasoline values which are roughly double the actual if you do not reset the stoic value.
The car would not even run at the values displayed on the sensor, proving it is not reading the air/fuel ratio.
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