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 Post subject: O2 question
 Post Posted: Fri Mar 30, 2012 5:04 pm 
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Will an O2 read differently with different octane gas? Will it read way lean if there's detonation? My CR is about 13.4:1, which is on the edge of Cam2 purple and Cam2 blue. I ran the same CR with a 270/280 cam and purple worked fine. I switched to a 262/270 cam and was afraid to run purple. I'm hoping that the O2 will show me what's what.


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 Post subject: Re: O2 question
 Post Posted: Fri Mar 30, 2012 7:15 pm 
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Ron,

I'm pretty sure detonation shows up on the O2 sensor as a lean reading, not a lean spike like a miss, but leaner than what it was reading before the detonation.

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 Post subject: Re: O2 question
 Post Posted: Fri Mar 30, 2012 7:38 pm 
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Ron, On the bottom of this graph is the 02. right bank is 12ish left bank is anywhere from 13.5 to 15 O:)
but there was nothing wrong at all except the O2 was dead on the on the left bank O:) ..So just be careful how you read them and won't be a bad idea to swap O2's...
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Here's is everything the same but a different day and the only thing I changed was the O2's
There is an advantage to having 8 EGT's
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 Post subject: Re: O2 question
 Post Posted: Fri Mar 30, 2012 9:44 pm 
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I've got a Racepak Sportsman on the way with only a single O2. You mean when they die they read lean? I need it to not read at all. I'll spend a few runs trying to fatten it when I need to replace it! I'm glad you told me that.


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 Post subject: Re: O2 question
 Post Posted: Fri Mar 30, 2012 10:16 pm 
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A misfire will send the O2 reading lean. And if a different fuel burns differently in the engine it will show up reading different on the O2's as well. Notice I didn't say octane, octane is only a resistance to detonation/preignition. It is possible to have a higher octane fuel burn better in an engine than a lower one.


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 Post subject: Re: O2 question
 Post Posted: Fri Mar 30, 2012 10:58 pm 
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jmarkaudio wrote:
A misfire will send the O2 reading lean. And if a different fuel burns differently in the engine it will show up reading different on the O2's as well. Notice I didn't say octane, octane is only a resistance to detonation/preignition. It is possible to have a higher octane fuel burn better in an engine than a lower one.

So the O2 will show lean if the engine is detonating, right?
In other words, If the AF is decent with 112 and I switch to 110 octane fuel, will I see a difference in AF?


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 Post subject: Re: O2 question
 Post Posted: Sat Mar 31, 2012 2:39 am 
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Octane alone has nothing to do with the readings on a wideband sensor.
A fuel density change will alter the AFR reading unless the correct change in jetting is done.
Fuel stoichiometric ratio changes dont affect Lambda and AFR is just a multiplier of Lambda.
A combined density and stoich change requires jetting compensation and a WB will read the change needed or not.
Detonation shows as a lean spike. Very mild detonation shows as a leaning of the cylinder. Thats detonation thats a long long way before you can see it on a plug.
Fuels with Oxygenates read as Leaner.
A Wideband is not an Oxygen sensor its a sensor that allows electronic controllers to count the number of Oxygen ions needed to achieve stoichiometry within the cell. If the Oxygen has to be removed from the cell via the electronic field then the answer is Leaner than stoich. if the Oxygen has to be added to the cell then the answer is richer than Stoich. Fuel with Oxygen causes problems with accuracy of readings if the Oxygen isnt used. The rouge Oxygen reduces the number of molecules that have to be passed into the cell (when running rich like racers do) therefor the electonics reports a leaner than truth mixture. Its not lean from atmosphere, its lean from internal oxygen. If the oxygen gets burnt then the reading will be true. Believe me LOTS of engines dont utilise the oxygen efficiently.
Proper full on detonation actually strips the Hydrogen bond away from the Carbon atoms, leaving soot behind and unused Oxygens, thus full on detonation reads really lean and blows black smoke.


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 Post subject: Re: O2 question
 Post Posted: Sat Mar 31, 2012 8:34 pm 
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shrinker wrote:
Octane alone has nothing to do with the readings on a wideband sensor.
A fuel density change will alter the AFR reading unless the correct change in jetting is done.
Fuel stoichiometric ratio changes dont affect Lambda and AFR is just a multiplier of Lambda.
A combined density and stoich change requires jetting compensation and a WB will read the change needed or not.
Detonation shows as a lean spike. Very mild detonation shows as a leaning of the cylinder. Thats detonation thats a long long way before you can see it on a plug.
Fuels with Oxygenates read as Leaner.
A Wideband is not an Oxygen sensor its a sensor that allows electronic controllers to count the number of Oxygen ions needed to achieve stoichiometry within the cell. If the Oxygen has to be removed from the cell via the electronic field then the answer is Leaner than stoich. if the Oxygen has to be added to the cell then the answer is richer than Stoich. Fuel with Oxygen causes problems with accuracy of readings if the Oxygen isnt used. The rouge Oxygen reduces the number of molecules that have to be passed into the cell (when running rich like racers do) therefor the electonics reports a leaner than truth mixture. Its not lean from atmosphere, its lean from internal oxygen. If the oxygen gets burnt then the reading will be true. Believe me LOTS of engines dont utilise the oxygen efficiently.
Proper full on detonation actually strips the Hydrogen bond away from the Carbon atoms, leaving soot behind and unused Oxygens, thus full on detonation reads really lean and blows black smoke.

Does fuel density mean weight? I'd be going from 5.9/gallon to 6.1/gallon for my test.


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 Post subject: Re: O2 question
 Post Posted: Sun Apr 01, 2012 7:11 am 
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yes fuel density is weight per gallon.


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 Post subject: Re: O2 question
 Post Posted: Sun Apr 01, 2012 11:05 am 
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shrinker wrote:
yes fuel density is weight per gallon.

So going to a heavier fuel would mean going to a larger jet to keep the AFR the same, correct?


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 Post subject: Re: O2 question
 Post Posted: Sun Apr 01, 2012 3:31 pm 
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Not necessarily. heavier fuel means that the weight of fuel delivered through a jet will be greater, if that was the only factor then that would make it richer. Remember AFR is set by weight of air verses weight of fuel. So when all you do is change the weight of the fuel to a heavier type you get more weight through the jets making the fuel side of the ratio more so its richer BUT you have to check if the fuel has the same stoichiometric ratio or not. Fuels vary from around 10.5 stoich ratio to just over 15 stoich for non oxygenated fuels. If your fuel has more weight but a leaner stoich point it may finish up with no change in jetting required, But you have to check. Its not a problem for low power per cube engines but when your getting up around 2hp or more per cube you gotta check this stuff out before destroying things.


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 Post subject: Re: O2 question
 Post Posted: Sun Apr 01, 2012 3:32 pm 
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Ron Gusack wrote:
So going to a heavier fuel would mean going to a larger jet to keep the AFR the same, correct?

Heavier fuel if thats the only chemical change requires SMALLER jets to keep the AFR the same.


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 Post subject: Re: O2 question
 Post Posted: Sun Apr 01, 2012 4:27 pm 
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shrinker wrote:
Not necessarily. heavier fuel means that the weight of fuel delivered through a jet will be greater, if that was the only factor then that would make it richer. Remember AFR is set by weight of air verses weight of fuel. So when all you do is change the weight of the fuel to a heavier type you get more weight through the jets making the fuel side of the ratio more so its richer BUT you have to check if the fuel has the same stoichiometric ratio or not. Fuels vary from around 10.5 stoich ratio to just over 15 stoich for non oxygenated fuels. If your fuel has more weight but a leaner stoich point it may finish up with no change in jetting required, But you have to check. Its not a problem for low power per cube engines but when your getting up around 2hp or more per cube you gotta check this stuff out before destroying things.

Okay. I was thinking that the lighter fuel would flow more easily given the same pressure as a heavier fuel and would require less jet.
It looks like the stoich ratios are 15 and 15.1.
I was hoping that the O2 would tell me definitively if the cheaper fuel would damage the engine.


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 Post subject: Re: O2 question
 Post Posted: Mon Apr 02, 2012 6:34 am 
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The viscosity of all grades of gasoline is the same or dam close to the same so the flow rate through the jets is the same. The weight of fuel per second flowing varies with the density so thats why heavier fuel requires a smaller jet, (stoich issues aside). What you do is you multiply the density by the stoich ratio for any fuel and then compare the answers. if the new fuel is a smaller number its going to run leaner by the differential percentage. If its bigger it will be richer etc. Thats how you calculate jetting correctly from one type of gasoline to another.
If your referring to a Wideband sensor as the O2 then yes it will tell you whats happening with the mixture. The perfect world is the sensor will report the correct lambda. Lambda is fuel independent, For instance if the lambda is 0.85 then the mixture is 15% (100 less 85) rich of stoich. The perfect world sensor will catalytic react all the incompletely combusted components and report the necessary oxygen transfer either in or out of the cell as rich or lean by a relationship to stoichiometric perfect combustion. Unfortunately engines are not perfect so its all stuffs up sometimes.


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 Post subject: Re: O2 question
 Post Posted: Mon Apr 02, 2012 10:27 am 
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If the viscosity is equal, then a lighter fuel would start flowing through the booster sooner, right? The high in the bowl and the low at the booster would pull the lighter fuel sooner, at least to my way of thinking. I'm learning here, so bear with me if you can.

I guess a simpler way of determining the presence of detonation would be a good EGT.


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