What A/F ratio do i want to have at what rpms? is it pretty much the same ratio throughout the powerband at WOT? What ratio do i want driving around town, not getting on it? thanks!

When you're driving around in town, your car will be trying to maintain a 14.7:1 afr. When you go WOT you want to see 11-12 over 3500rpm or so. Below that you can be a bit leaner to help spool. Each engine will be slightly different, and with a standalone you can play with timing and air fuel ratios to find the best combindation -- but 11.5:1 is a safe number...

I need to go find a good book to read on this stuff.

Is it alright, when I'm feathering the throttle to maintain a constant speed to see numbers jumping all over the place? anywhere from 13-16, somtimes 17?

When is it dangerous to be to lean, just when you're at WOT?

When I was logging a few runs on the current setup I was pretty lean (~13) till positive pressure then it richened up to safty... is that alright?

I need to go find a good book to read on this stuff.

Is it alright, when I'm feathering the throttle to maintain a constant speed to see numbers jumping all over the place? anywhere from 13-16, somtimes 17?

When is it dangerous to be to lean, just when you're at WOT?

When I was logging a few runs on the current setup I was pretty lean (~13) till positive pressure then it richened up to safty... is that alright?


All perfectly normal. When you are over 2000rpm and let off the throttle completely, you will be off-the scale lean. During cruise you should be 14-15, and during WOT you should drop down to rich...

If you are using a narrow-band sensor (stock o2) and an autometer type gauge you will see the lights dance because the narrow-band signal is like an on-off switch that tells the ECU only that it is above or below 14.7:1

During warmups around 12.0:1 is fine.
After warm up almost all major production cars are running at 14.7:1 air fuel aka lamba during cruizing, idle, acceleration. However if you have a AEM you can go leaner to 15.8:1 at times which has been known to add 6-8MPG. However you risk running much hotter.
However if they are at wide open throttle (WOT) most production cars are around 10.9:1 air fuel. Models fluctuate.

Wide open throttle guildeline
Most power to be gained at WOT is I believe 12.5:1.
NA cars shoot for around 12.1:1
Forced induction 11.3:1
Forced induction with Methanol 10.90:1

Good info Need4Speed. For what its worth, the reason manufacturers do not go leaner than 14.7:1 is because of NOx emissions

Good info Need4Speed. For what its worth, the reason manufacturers do not go leaner than 14.7:1 is because of NOx emissions

Okay I've heard both stories.
1.) Going leaner than 14.7:1 creates more heat
2.) Going leaner than 14.7:1 creates more NOx

I've heard both situations from several sources. Personally in my mind it won't cause more heat because it's less fuel in the engine. However running excessive timing can burn valves.

The main reason manufacturers use 14.7 to 1 is because of catylitic converter efficiency. If you have no cats.....you have no worries. I run my Supra at 16.8 to 1 at cruise and get 28-29mpg on trips. When there is no load, there is no heat (at least not enough to worry about). As for cold start up, don't worry about what the O2 is telling you while the car is warming up. The O2 is essentially telling you what is coming out of the combustion chamber. When the engine is cold, more fuel is required because it collects on the colder metal in the intake and cylinder head, this essentially takes the fuel out of suspension in the air and you get pockets of fuel being burned rather than a good clean combustion. So run whatever that particular engine seems to be happiest with.

Jason.

1badsupra have you tired to compare your mpg for 16.8:1 to 14.7:1? I bet you probably pick up 9mpg?

When the engine is cold, more fuel is required because it collects on the colder metal in the intake and cylinder head, this essentially takes the fuel out of suspension in the air and you get pockets of fuel being burned rather than a good clean combustion.


Cool, I never knew that was why you needed to be rich on warm-up...

I want better MPG!!!! :bonk:
-jt

Cool, I never knew that was why you needed to be rich on warm-up...

called condensation

i put mine up to 16.5:1 initially it surged a little. Then I adjusted the base map so it woudln't fluxuate as much. Ran fine from that point forth. HOpefully i can get some 20mpg with city/freeway mixed :)

I saw a tech article on using a resistor for a narrow band O2 for a modern production car. I wonder if it would be wise to go to say 15.8:1 on say a Ls1 with cats in place that is if you don't care about emissions or would this only be wise if you have H pipe?

I remember when I had my stock supra on long freeway drives it got exactly what the supra sticker said it would get 22mpg on the freeway.

Be careful, leaner than 15:1 can kill the converter if you have one.

BTW to elaborate on an earlier post(s)... 14.7:1 is the chemically ideal balance of mass of air to mass of gasoline. Ideally this produces the least amount of harmful exhaust gases, uses all the available oxygen in the air, and reduces the amount of work the converter has to do. If you exceed 15:1 the converter temperature will get extremely hot and can permenantly damage the chemical loading and ultimately the substrate of the converter. If the A/F gets consistantly leaner than 14:7, a factory ECM will go drastically rich to cool the exhaust temps and prevent converter melt down. That is why they run so rich. Run it lean as they can then cool it off.

Calculating the mathmatical balance is called stoichiometry, the actual ratio is stoiciometric. This chemical balance exists for any fuel but the ratio will differ as the chemical make up of the fuel differs. Best power A/F varies with the fuel and engine design but roughly 12.5 is a target. going richer up to 11:5 is safer on pump fuel and won't create a significant loss of power over 12:5. A/F for best power can change per RPM, but you won't need to be that concerned with a street car.

Incidentally Methanol stoich is 6:1, best power around 4:1. Ethanol stoich is 9:1 best power about 7:1.

Be careful, leaner than 15:1 can kill the converter if you have one.

BTW to elaborate on an earlier post(s)... 14.7:1 is the chemically ideal balance of mass of air to mass of gasoline. Ideally this produces the least amount of harmful exhaust gases, uses all the available oxygen in the air, and reduces the amount of work the converter has to do. If you exceed 15:1 the converter temperature will get extremely hot and can permenantly damage the chemical loading and ultimately the substrate of the converter. If the A/F gets consistantly leaner than 14:7, a factory ECM will go drastically rich to cool the exhaust temps and prevent converter melt down. That is why they run so rich. Run it lean as they can then cool it off.

Calculating the mathmatical balance is called stoichiometry, the actual ratio is stoiciometric. This chemical balance exists for any fuel but the ratio will differ as the chemical make up of the fuel differs. Best power A/F varies with the fuel and engine design but roughly 12.5 is a target. going richer up to 11:5 is safer on pump fuel and won't create a significant loss of power over 12:5. A/F for best power can change per RPM, but you won't need to be that concerned with a street car.

Incidentally Methanol stoich is 6:1, best power around 4:1. Ethanol stoich is 9:1 best power about 7:1.

To re-iterate, Stoich doesn't mean *&it to the engine.....just the cat. So if you don't have one it again.....is a useless number, unless ofcourse you are trying to be as evironmentally safe as you can be with no cat!

Be careful, leaner than 15:1 can kill the converter if you have one.

BTW to elaborate on an earlier post(s)... 14.7:1 is the chemically ideal balance of mass of air to mass of gasoline. Ideally this produces the least amount of harmful exhaust gases, uses all the available oxygen in the air, and reduces the amount of work the converter has to do. If you exceed 15:1 the converter temperature will get extremely hot and can permenantly damage the chemical loading and ultimately the substrate of the converter. If the A/F gets consistantly leaner than 14:7, a factory ECM will go drastically rich to cool the exhaust temps and prevent converter melt down. That is why they run so rich. Run it lean as they can then cool it off.

Calculating the mathmatical balance is called stoichiometry, the actual ratio is stoiciometric. This chemical balance exists for any fuel but the ratio will differ as the chemical make up of the fuel differs. Best power A/F varies with the fuel and engine design but roughly 12.5 is a target. going richer up to 11:5 is safer on pump fuel and won't create a significant loss of power over 12:5. A/F for best power can change per RPM, but you won't need to be that concerned with a street car.

Incidentally Methanol stoich is 6:1, best power around 4:1. Ethanol stoich is 9:1 best power about 7:1.


Wow....... Someone paid attention in school!! I bet you're a really good mechanic for Toyota!

unless ofcourse you are trying to be as evironmentally safe as you can be with no cat!


We tune all of our race cars to pass all local emmission laws without the need for a catalytic converter...... Um sure we do...

To re-iterate, Stoich doesn't mean *&it to the engine.....just the cat. So if you don't have one it again.....is a useless number, unless ofcourse you are trying to be as evironmentally safe as you can be with no cat!

`zactly! Its just a number thing to create an "ideal burn" but certainly not the means to an end or an engine requirement.

I'm not exactly a mechanic for Toyota, but thanks for the kind words.

I'm not exactly a mechanic for Toyota, but thanks for the kind words.


Well you should be!! I bet you could be head mechanic at a dealership in no time at all!

With all due respect to the technicians, that would kinda be a step backwards. I'm who the dealers and field staff call when they can't figure something out. I just don't advertise what I do for obvious reasons.

Excellent post, I learned a lot and cleared up some other things I was thinking about. I will be tuning my car soon, and I'm NA with a full freeflowing exhaust. I'm tuning because there are no more mods left that I can do, aside from the very expensive and going internal. I will be turboing soon so I don't see the point in spending even more money for minute gains. I currently have a completely freeflowing exhaust without any cats. This will mean that I can run leaner than usual and not have to worry about the heat of the catyltic converter or exhaust components (They are heatwrapped). I can't wait to get an SAFC and start tuning. Any input or advice for me?

Sure, leave it uncorrected at less than 70% throttle and have the SAFC alter the signal above that. Otherwise any changes you make will just be corrected by the computer and then affect/mess up your WOT changes.

Yea I understand the closed loop and open loop etc., I just didn't realize that the catyltic converter played that much of a role in tuning. This thread also cleared up all the AF ratio questions I had, so thanks once again. :)

With all due respect to the technicians, that would kinda be a step backwards. I'm who the dealers and field staff call when they can't figure something out. I just don't advertise what I do for obvious reasons.

Yeah i remember changing Jasons tranny out at our local Toyota dealership and just being blown away by your knowledge. Actually i think everyone there was!!! That was too freakin cool :headbang:

actually, EGT's dont skyrocket when going leaner than 14.7:1 ratio.

EGT's will begin to cool off after 14.7:1 because you start to have less fuel available to combine with the existing O2 in the cylinder. when you are missing one of the 3 ingredients for combustion, you have smaller fire and less heat. EGT's are hottest at 14.7:1 and will be cooler on either side of stoichiometric for the plain reason that you either have less fuel or less O2. when you have the "right" amount, 14.7 lbs of air for 1 lb of fuel, you have peak combustion efficiency to acheive the most heat. the problem with running internal combustion engines at load with a 14.7:1 AFR on pumpgas is because we do not have the Anti-knock index availble on pump gas, and the fact that modern metals that are widely used in production engines cannot handle sustained temperatures that stoich AFR's yeild while under load. those two factors prevent us from harnessing the full potential of the chemical combustion process. that is why we need to shoot for richer AFR's to be safe and keep EGT's to a level that will preclude engine meltdown.

now, for acheiving lower EGT's and peak fuel economy, it is possible to run engines leaner than stoich. people obviously do it now, and experience good results.

and the reason engines run rich on initial start up is because a cold engine saps out alot of the heat created by combustion. when most of the heat is sapped out due to cold combustion surfaces, the cylinder pressures are lower than that of an engine at operating temp. thats why its so much harder to start an engine at sub zero climates, especially diesel engines. its partially also due to the fact that fuel precipitates out, but its mainly due to the fact that the heat of combustion is rapidly consumed by the cold metals in the cylinders. its easier to start an engine with more fuel because there is more fuel there to light off and easier to begin combustion. the rich AFR's for start up arent necessarily to raise EGT's to assist in cold start emissions and reduce the delay in cat lightoff. the attempt to reduce the delay in cat light-off is indicated by the factory's integration of high idle and idle-up after inital startup. just like the supra typically cold starts, and the RPM's immeditely rise to 1500-1800. this is supposed to aid the light-off of the cat, similarly for cold idle at 1200rpm. a PRIMe example for this process is the Rotary. FC's and FD's cold start and IMMEDIATELY jump up to 3000rpm, stay there for 15 seconds, drop down to 1500rpm and then slowly drop down to 750 as the coolant temp rises. the 3000rpm start after initial crank-up is to light off the cats.

hope that clears up a bit of info.

Thats a lot of typing. Unfortunatly not 100% correct. I am not going to respond to all of it because I don't have the time at the moment, but I will if necessary. First off catalytic temperature and EGTs are not the same. The catalytic process is not dependant entirely on EGTs but the secondary combustion within the converter. EGTs warm the catalyst but are not the only source of heat. At 15:1 or more, the secondary combustion process in the converter (the actual conversion of gases) is its own demise not the EGTs. To be more specific, at approximately 800c catalyst bed temperature, chemical loading damage occurs and at 850c substrate damage will occur. That is independant of EGTs to a degree and dependant on residual oxygen content of the exhaust charge. Oxygen content is directly associated with A/F. Hence 15:1 (specific oxygen content) causing damage.

Secondly EGTs will continue to rise in a lean combustion enviornment until lean misfire occurs. This can be WELL past 14.7:1. The decrease occurs only when the combustion process partially occurs from the lack of fuel ignition. Unburned oxygen (and atmosphere) passes out of the combustion chamber and the temps drop. This is why tuning with EGTs is inaccurate as you can have cold EGTs and an overly lean mixture. You would interpret the EGTs as rich and continue to lean it out.

The engine is run rich when cold because cold engine surface temperatures condensate fuel. Liquid fuel does not burn so you increase fuel volume in an attempt to increase the available amount of vaporized fuel present in the combustion process. A/Fs can be as low as 2:1 by volume in a cold engine but actual vaporized fuel in the chamber is 12-13:1 usable fuel vapor.

A few reasons for RPM increase when cold is due to entropy within the cylinder at lower RPMs and engine friction causing lower RPM stability issues from combustion entropy.

Thats a lot of typing. Unfortunatly not 100% correct. I am not going to respond to all of it because I don't have the time at the moment, but I will if necessary. First off catalytic temperature and EGTs are not the same. The catalytic process is not dependant entirely on EGTs but the secondary combustion within the converter. EGTs warm the catalyst but are not the only source of heat. At 15:1 or more, the secondary combustion process in the converter (the actual conversion of gases) is its own demise not the EGTs. To be more specific, at approximately 800c catalyst bed temperature, chemical loading damage occurs and at 850c substrate damage will occur. That is independant of EGTs to a degree and dependant on residual oxygen content of the exhaust charge. Oxygen content is directly associated with A/F. Hence 15:1 (specific oxygen content) causing damage.
i will guarantee you that EGT's on cold startup play a significant factor in cat operation. cold start emissions are the bane of OEM's. they program a high idle to help light off the cat and get it to operating temperature Faster. that is why some companies install the cat right on the exhaust manifold like hondas and nissans.

Secondly EGTs will continue to rise in a lean combustion enviornment until lean misfire occurs. This can be WELL past 14.7:1. The decrease occurs only when the combustion process partially occurs from the lack of fuel ignition. Unburned oxygen (and atmosphere) passes out of the combustion chamber and the temps drop. This is why tuning with EGTs is inaccurate as you can have cold EGTs and an overly lean mixture. You would interpret the EGTs as rich and continue to lean it out.
You are absolutely incorrect. On a Gasoline engien, the EGT's will be lower at a value below Lambda. when Lambda reaches 1.0, EGT's will peak. When Lambda reaches a value Greater than 1.0, EGT's will begin to decrease. this is why its difficult to tune via EGT's. if you are already on the lean side of Lambda, and you try to lean out the AFR in an attempt to gain more power, the EGT's will continue to cool off since you are already on the lean side of Lambda

The engine is run rich when cold because cold engine surface temperatures condensate fuel. Liquid fuel does not burn so you increase fuel volume in an attempt to increase the available amount of vaporized fuel present in the combustion process. A/Fs can be as low as 2:1 by volume in a cold engine but actual vaporized fuel in the chamber is 12-13:1 usable fuel vapor.

A few reasons for RPM increase when cold is due to entropy within the cylinder at lower RPMs and engine friction causing lower RPM stability issues from combustion entropy.

I feel that your point is valid and exists in conjunction with my point in my previous post. engines refuse to run smoothly when they are cold because the heat of combustion is sapped out of the cylnder by the cold surfaces, IN ADDITION to the reason you have stated; atomized fuel molecules tend to recombine and fall out of the air stream and do not combust readily. as a fuction of cold start, fuel enrichment is necessary. once the engine is started, the RPM is high for a few reasons; one to light off the catalytic converter for peak cold-start emissoins reduction AND as the reason you mentioned about unstable engine operation at low rpm's when engine internals are cold.

If i had a EGT gague i would tell you guys what happens on freeway cruizing from going 14.7:1 - 16.5:1. I personally have noted no difference in driving the supra at my 60mph cruizing air fuel of 16.5:1. Coolant temperature seems fine so does Air intake temperatures. But as the load increases i do have it going richer and richer closed loop mode.

AEM's are cool :)

[QUOTE=flubyux2]actually, EGT's dont skyrocket when going leaner than 14.7:1 ratio.

EGT's will begin to cool off after 14.7:1 because you start to have less fuel available to combine with the existing O2 in the cylinder. when you are missing one of the 3 ingredients for combustion, you have smaller fire and less heat. EGT's are hottest at 14.7:1 and will be cooler on either side of stoichiometric for the plain reason that you either have less fuel or less O2. [QUOTE=flubyux2]

This is your original statement... EGTs absolutely play an exclusive role in catalyst warmup. No debate there. You are missing what I said about catalytic bed temperatures and damage. An engine can survive on 15:1 but that is the area that the SECONDARY CATALYST COMBUSTION causes cataylist damage and destroys itself. Also the statement about lean A/Fs and EGTs is like I said not 100%correct. Tempatures drop specifically as a result of a lack of combustion IE misfire. And misfire does not only include a complete lack of combustion but areas within the combustion chamber that do not burn. That is where the lack of heat comes from. You can have complete combustion past 14.7:1. but due to lack of thermal mass of the fuel, and other reasons heat is higher. EGTs will drop purely as a result of misfire. NOT just at 14.7, it occurs more like 16.5:1 depending on combustion chamber effiecency.

It is called a warmup cat and is typically chemically loaded to lightoff at lower catalyst temperatures. Catalyst bed temp is forcasted by engine load at a given rpm (over a given time)and a/f ratio trends etc. The ECM intentionally controls and calculates this

How is your Lamda statement different than what I said? I'd be curious to know if you can define lambda and is it different for say alcohol since you mentioned lambda for gasoline?

In addition? That is what condensate means.

I'm not attempting to critique your knowledge as I think you do understand more than most but you are missing some key fundimentals in your thought process and I am attempting to clarify them for you. I do not currently have the time to spend forever on this subject as I am ironically enough typing this from a hotel in Japan as I am out here on a training/information trip at TMC's training center..... Just so you understand who you are attempting to set straight. There is WAY more to this then 99% could comprehend.

well i do appreciate you taking time to speak with me about this while on your training. i also feel that i could learn some great information from you as well. if there is anything i can learn from you, itd definitly be AEM EMS-based ;)

I believe that we were trying to convey the same thoughts however i wasnt correlating my ideas to yours. the way you say it makes it seem to be one and the same.

Lambda is supposed to be the numeric value for air-fuel equivalence. Lambda values would be the same in any engine. i said the wrong thing, since i was thinkin about stoich values differing, but Lambda is the result of a mathmatical equation based off ratios, regardless of fuel type.

well i do appreciate you taking time to speak with me about this while on your training. i also feel that i could learn some great information from you as well. if there is anything i can learn from you, itd definitly be AEM EMS-based ;)

I believe that we were trying to convey the same thoughts however i wasnt correlating my ideas to yours. the way you say it makes it seem to be one and the same.

Lambda is supposed to be the numeric value for air-fuel equivalence. Lambda values would be the same in any engine. i said the wrong thing, since i was thinkin about stoich values differing, but Lambda is the result of a mathmatical equation based off ratios, regardless of fuel type.

My point was in the details. That is what I teach to others as that is the true understanding. To elaborate on Lambda... it stands for excess air ratio. Lambda at stoich (the chemical balance of combustion) is the same for any fuel. If it is at stoich it will be at 1. Since rich combustion lacks exhaust oxygen, the percentage will be less than one. Lean above one. You might notice if you do the wizard for alcohol in your AEM, the voltage curve doesn't change only the units do!

Good job. Keep educating yourself as you have a good jump on most others. Remember the intent of engine management is the same regardless of brand. The engine doesn't care what brand is running it or even if its a carb. Learn engine and combustion dynamics and the rest is just a particular brand of software usage.

Dave

thanks for the acknowledgment dave. i prefer to think im not a dunce and that i pretend to know what im doing. and im not comfortable saying "i dont know whats wrong". so i need to find information and learn more, be it resources or individuals. i have about as good an understanding as i can get short of being a chemical engineer or thermal dynamicist.

i knew Lambda was a function of a calculation based on ratios, so i can naturally see that i wont change with fuels or engines. im just not familiar with it as i dont use it on a regular basis to tune cars.

im glad you mentioned lean misfire as the cause of EGT's falling off above 15:1, i didnt put 2 and 2 together at that point. i was originally going by the premise that it only occurse above 16:1. im glad i know this now.

btw, if you ever get spare time, i would love to talk AEM maps with you.