Originally Posted by 02sierraz71_5.3

I dont agree with this 14.7 is perfect for what? Its not perfect for power NA or FI and its far from being perfect for great gas mileage.

The only reason our cars run at 14.7 is because it is mandated by the EPA because it is stoich (least hydrocarbon emmisions) but here is a question does it produce less pollution to run at 14.7 or does it produce less to not have to make all the extra billions of gallons of gas that are waisted by running at 14.7. Catalytic converters are in the same boat they produce nitrous oxide a greenhouse gas that is 300x more potent than carbon dioxide. I read an article in the NY times that states the EPA did a study in 89 and realized that late model engines with cats actually produced more greenhouse gases that engines without cats!!!!!

Originally Posted by Yelo

Blah Blah...the particular oxide of nitrogen that comes out of a catalytic converter consists of one part oxygen and two parts nitrogen - or N20, is that scientific enough for you

Originally Posted by dewmanshu

In closed loop, unless you are Holden, you can't shoot for anything higher than stoich from my understanding. Coomand 15:1 all day but it will still shoot for 14.7. Open loop, different story.

From your smoothing ve thread...

Originally Posted by EC_Tune

The fuel loop control averages the o2 sensor values to come up with an average o2 sensor value. This value is compared to the B1S1 and B2S1 tables to see if the fuel needs to be increased or decreased to stay at 14.7 AFR.
By telling the PCM to use a lower average millivolt value (350 instead of 451) it will drive the fuel correction lower and give you a slightly leaner air fuel mixture even though the o2 sensors are only correct at 14.7 AFR.
Think of it like your thermostat at home. If it's hot, the heater turns off, if it's cold it turns on. No midpoints just On or OFF. If you could average the temperature of your house and have the heater turn on and off "just when you are home" and keep it between 68-70 degrees, your heating bill goes down. These tables work in a similar way.
If you are in PE mode, the o2 sensors are ignored you just get more fuel period. If you are in Deep DFCO, the o2 sensors are ignored as well it's turning the fuel off instead of on. No feedback corrections just "On & Off" like the heater.
The General Airflow vs Mode determines which part of the B1S1 (or B2S1) vs Airflow table you are on.
The B1S1 & B2S1 tables determine how rich or lean the AFR might be biased.
BTW: If you are monitoring STFT+LTFT, and wideband AFR you will probably notice that the measured AFR in Closed loop moves around a bit with airflow at mild cruise & idle (check in steady state conditions). That's the bias that the B1S1 & B2S1 tables apply to achieve the correct AFR.

Originally Posted by BlownChevy

Ummmm you might want to rethink that statement.....If a Catalytic converter produces Nitrous Oxide then I am going to re-plumb my exhaust back into my intake.

Originally Posted by dc_justin

I don't think you understand the theory fully.

Originally Posted by dc_justin

What that theory does not leave room for is the situation that almost always occurs which is that in the limited time available for that combustion event to occur, not all gasoline molecules will be able to pair up with oxygen molecules for a complete burn. That is why running slighty richer will net more power than stoic. Less opportunity for the random oxygen molecules to hide out and avoid the flame.

Originally Posted by Wilde Racing

This was posted on the HPTuner forum

Originally Posted by dc_justin

I don't think you understand the theory fully. For a given amount of fuel, there is a finite and definite amount of oxygen that is required to burn that fuel completely. That amount works out to be 14.7lbs of air to 1lb of fuel. If there was a completely uniform and perfect distribution of air and fuel, 14.7:1 would be the peak power point (any richer would be just unburnt fuel and lower the temperature of the combustion event, reducing peak pressure) while also having the lowest emissions.

Originally Posted by BlownChevy

I think it will be fun to have an open discussion on Air Fuel Ratio, there is allot to be learned and it will help myself and others with the topic.

16.0:1 LEAN

14.7:1 Stoich / Lamda

12.0:1 Rich

N/A 12.8 - 13.2 Ideal

Boost 11.8 - 12.2 Ideal

Boost / N20 11.0 - 11.8

As I too am learning as I go, here is one interesting fact that I picked up: 14.7:1 is considered perfect AFR due to the fact that it is as close to a 100% burn of the fuel as you can get.

I hope we can keep this on topic and educational. Could be beneficial to all.

Originally Posted by 02sierraz71_5.3

Im the one that doesnt understand?
If the above statement had any validity it would mean that engines would make max power at 14.7 which just isnt the case. Max power(also known as torque/ hp is a derivative of tq) isnt produced at stoich afr doesnt matter what engine your running. Reducing combustion chamber temp is a huge part of running richer it allows you to run more timing and also saves you from problems like melting pistons and blowing ring lands off. And on top of it you make more power under the curve and thats what wins races. So what if its not a stoich combustion, the point is mute because Im out to make power and win races and peak power doesnt occur at stoich AFR.
Id like to see you argue that point with anyone who has tuning and dyno experience, it just doesnt hold up in the real world with 93 octane gas and imperfect conditions.

Originally Posted by dc_justin

No, you don't appear to understand the topic as it is being discussed. I've explained why stoic does not work in practicality, but that doesn't change the fact that it is the ideal fuel mixture, what don't you understand about that? Your previous post questioned why 14.7 was deemed as "best" by the EPA, and my post answered it.
For any given mixture, ONLY enough fuel can burn to combine with the available oxygen. IDEALLY, in a PERFECT world without detonation, that amount of fuel is 1 lb for 14.7 lbs of air. Any more fuel will remain unburned and wasted. It's not that hard to understand.