# Air Fuel Mixture



## LOWET (Oct 21, 2007)

Not sure if this has been covered before. Sorry if it has.

I am curious as to what is a good A/F mixture under normal driving conditions. I heard that the 04-06 GTOs run a mixture of around 13.5 on a stock tune and I would like some information on how the number read. If the numbers are higher then 13.5 does this mean that the car is running richer or is it more of a lean condition. 

What about driving on the street. Is it safer to run with a mixture that is slightly RICHER or with a mixture that is slightly leaner .

In general. What would be a decent A/F mixture for every day driving. 

Sorry if these questions sound stupid , I just had a Wide Band gauge installed and I would like to know what I am looking at when watching it.

Thanks
John


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## jpalamar (Jul 22, 2008)

Visit a tuning forum. There is allot of great info on them that came help. I think mine is tuned at high 12s if I remember right.


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## svede1212 (Nov 1, 2005)

what wideband gauge did you get? all GTOs run on cruise an AFR of 14.7 to 1. the front narrowband O2 sensors see to that. it's the WOT or power enrichment that's very rich stock. LS1s make the most power roughly around 12.8-13.0 AFR in PE mode and LS2s seem to like 12.6-12.8 AFR. the factory PE is around 12 or lower which is very "safe" but pig rich. tuning the PE AFR along with timing are the primary things that are done to gain more horse power out of a stock car. AFR is the ratio of air by weight to fuel by weight with the "fuel" part of it implied as "1". 14.681 is considered stochiometric or the perfect blend for gas as each O2 has 1 molecule of gas to combine with. in PE you need more fuel because of the characteristics of the burn in the cylinder to make the most power. because of that "rich" or "lean" depends on if you're talking about cruising or PE. so an AFR of "12" is 12 parts air to 1 part fuel and is rich under most NA circumstances and an AFR of 15 is lean under all circumstances.


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## jpalamar (Jul 22, 2008)

svede1212 said:


> what wideband gauge did you get? all GTOs run on cruise an AFR of 14.7 to 1. the front narrowband O2 sensors see to that. it's the WOT or power enrichment that's very rich stock. LS1s make the most power roughly around 12.8-13.0 AFR in PE mode and LS2s seem to like 12.6-12.8 AFR. the factory PE is around 12 or lower which is very "safe" but pig rich. tuning the PE AFR along with timing are the primary things that are done to gain more horse power out of a stock car. AFR is the ratio of air by weight to fuel by weight with the "fuel" part of it implied as "1". 14.681 is considered stochiometric or the perfect blend for gas as each O2 has 1 molecule of gas to combine with. in PE you need more fuel because of the characteristics of the burn in the cylinder to make the most power. because of that "rich" or "lean" depends on if you're talking about cruising or PE. so an AFR of "12" is 12 parts air to 1 part fuel and is rich under most NA circumstances and an AFR of 15 is lean under all circumstances.


:agree


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## svede1212 (Nov 1, 2005)

FWIW one of the beauties of the '04 is that it came over with the Aussie computer. they had a feature that was turned off here called "lean cruise" that puts the car into a programmed AFR that can go as high as AFR 17 to 1 under light cruising conditions. lean conditions make for higher temps as fuel helps cool the cylinder so that and knock are why you don't want that under PE. as the load and throttle is very light under lean cruise it's not a problem and you can up your gas mileage a good 10+% by re-enabling it. the reason it's turned off here is because lean conditions make more nitric oxide which is a component of smog. seeing as less gas also means less "carbon emissions" IMHO it's a win-win for gas usage and your pocketbook.


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## LOWET (Oct 21, 2007)

svede1212 said:


> what wideband gauge did you get? all GTOs run on cruise an AFR of 14.7 to 1. the front narrowband O2 sensors see to that. it's the WOT or power enrichment that's very rich stock. LS1s make the most power roughly around 12.8-13.0 AFR in PE mode and LS2s seem to like 12.6-12.8 AFR. the factory PE is around 12 or lower which is very "safe" but pig rich. tuning the PE AFR along with timing are the primary things that are done to gain more horse power out of a stock car. AFR is the ratio of air by weight to fuel by weight with the "fuel" part of it implied as "1". 14.681 is considered stochiometric or the perfect blend for gas as each O2 has 1 molecule of gas to combine with. in PE you need more fuel because of the characteristics of the burn in the cylinder to make the most power. because of that "rich" or "lean" depends on if you're talking about cruising or PE. so an AFR of "12" is 12 parts air to 1 part fuel and is rich under most NA circumstances and an AFR of 15 is lean under all circumstances.





Thanks again for your information. You always come thru with facts to back up your statements. I was curious as to my A/F readings since my Procharger install. At idle or under 1800 RPM driving it seems to stay right around 14.4-14.8 and comes down to around 12.8-13.2 as RPMs climb. I have not done any full throttle runs yet because I am breaking in a new Stage 6 Transmission from RPM/MONGILLOS and only have around 150 miles on it. 

Do my readings seem safe to you. Don't know if it means anything but the did a Speed Density when my P-1 was installed.

JOHN


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## svede1212 (Nov 1, 2005)

the idle/low RPM is great but i doono tho. in power enrichment with boost it's usually in the 11s unlike NA. speed density tunes are time consuming and i hope he took the time to do it right


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## Poncho Dan (Jun 30, 2009)

Good thread, learning alot, though I knew optimal stoich was like 14.7:1 from an autos teacher I had in HS. Where would be a good place to start learning about tuning?


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## LOWET (Oct 21, 2007)

svede1212 said:


> the idle/low RPM is great but i doono tho. in power enrichment with boost it's usually in the 11s unlike NA. speed density tunes are time consuming and i hope he took the time to do it right


I took itout for a little ride today. As before, at idle or real low RPMs it was around 14.5- 14.8. on the gas a little it went to around 13.5 


On the hiway @ 70 MPH [ around 2100 RPMs ] it seemed to stay right at 13.8 give or take 

a 1/2 throttle run from 70 to 100 MPH gave a reading about 11.6

I tried a full throttle run from 50 MPH but I did not get a chance at a reading. Car lost traction so I let off and came back home


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## svede1212 (Nov 1, 2005)

LOWET said:


> I took itout for a little ride today. As before, at idle or real low RPMs it was around 14.5- 14.8. on the gas a little it went to around 13.5
> 
> 
> On the hiway @ 70 MPH [ around 2100 RPMs ] it seemed to stay right at 13.8 give or take
> ...


sounds about right altho exhaust gas temp and knock are the main things to see if you're OK. your 11.6 is in the normal "safe" AFR for boost PE


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## LOWET (Oct 21, 2007)

svede1212 said:


> sounds about right altho exhaust gas temp and knock are the main things to see if you're OK. your 11.6 is in the normal "safe" AFR for boost PE


Thank you again. The shop that did my work told me they did a very safe tune to my car but I just wanted a second opinion.


John


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## Poncho Dan (Jun 30, 2009)

What does "speed density" or a "speed density tune" mean?


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## svede1212 (Nov 1, 2005)

Poncho Dan said:


> What does "speed density" or a "speed density tune" mean?


it's a way to do fueling without the MAF. the MAF infers air volume by converting input into a frequency that's referenced by a table. speed density infers air volume by referencing a table (volumetric efficiency) of RPM and manifold pressure. MAF tunes are a lot easier to do as you don't have to build a whole VE table with ~170 cells. the VE can also change over time as the engine wears but the front O2s keep all but power enrichment in line as long as they're close. speed density has been and is still used by some manufacturers. i believe that LT1s used it.

VE sounds complicated but it isn't. the amount of air that a static cylinder can hold when the piston is all the way down would be a "100" like 100% of the cylinder would be held with x amount of air depending on pressure. when the throttle is partway open there is a vacuum in the manifold and the cylinder doesn't hold the same amount of air so the fueling percentage is less. the low end of "efficiency is about 30 and the high end can be ~100 with NA. for every RPM and pressure there's a number that needs to get filled in the VE table and you now know how much O2 so the comp will know how much fuel to put in.


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