Ok, here are my thoughts; feel free to correct me <U>if</U> I am wrong....Which I may be.

1-I understand that <U>stoich</U> is neither;
a) The ratio at which an engine produces the most power.
b) The ratio at which the engine is most efficient.

2-From my understanding <U>stoich</U> is the ratio at which the <U>catalytic converter</U> is most efficient

Now after looking into several "afr" labeled post on HT I realize that not too many guys on here will on here will go beyond a 15:1 afr at idle or cruise. Now granted that many newer lean burn engines that run ratios of 22:1 have very powerful ignition systems and some use GDI, I can't see it being too unreasonable for one of the honda's on this board to sucessfully run 16:1 without "major" mods.

Now the only plausible reason for running an afr like this would be to save gas while idling or cruising on the highway but who wouldn't want a few extra miles out of their gallon? Theoretically this wouldn't hurt your horsepower at all either except at idle or cruise, keep in mind that the average car requires about 12-14 hp to keep it at cruising speed.

Well now for the input, if all tuner's on here could post up their idle/cruise afr, with correlating octane and also the point that they will not cross due to detonation or preignition (which would hurt gas mileage due to the ecu compensating).

I expect not too many will care about this post but if you do post I highly appreciate it.

*Note: Engines runnning leaner produce higher NOx due to higher combustion chamber temps therefore creating ozone and bringing about humanity's demise just that much sooner*

 

stoich would be the point where the cat doesn't even need to be working (complete burn of all the fuel in the combustion chamber...which never happens anyway) you can run higher than 14.7 for idle or cruise but seems to me my car doesn't run right at higher AFR's...(maybe because of my large injectors though)

 

SO is it safe to assume that the leanest anyone on this forum goes is 14.7:1 or just that no one here tune their own cars?

ALthough I hadn't considered a larger injectors ability to perform at very low duty cycles.......hmmm

 

at idle my car likes anywhere between 14-15.5....it usually idles right at 14.7 though. For cruising i like to keep it around 14.5-15.5. I get the best gas mileage i've ever had even when the engine was the stock d16z6 (now its a built b16). I run open loop full time in my car.

 

Open loop? but why? WHat ems are you using?

 

i'm using cromepro. I use open loop b/c i've tuned my maps very well and it runs great in open loop, so theres no need for an o2 sensor to try and make corrections on a well tuned map. All of the cars that i tune i leave in open loop, i don't want an o2 sensor messing up the hours of work i did tuning a car.

 

14.7:1 is not when the engine burns all of the fuel, that would be no fuel in the exhaust which will only happen when you're decelerating in gear. (injectors off)

please read this for an idea of what this means.
http://en.wikipedia.org/wiki/Air_fuel_ratio

A tuner who is much wiser than I once told me that as long as the engine doesn't stumble, there is zero load on it at idle so why not run leaner.

I tune for ~15.4:1 at idle or even leaner depending on the engine.

closed loop will pull the A/F to 14.7 based on the narrow band O2 input.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Relic1 &raquo;</TD></TR><TR><TD CLASS="quote">14.7:1 is not when the engine burns all of the fuel, that would be no fuel in the exhaust which will only happen when you're decelerating in gear. (injectors off)

I tune for ~15.4:1 at idle or even leaner depending on the engine.

closed loop will pull the A/F to 14.7 based on the narrow band O2 input.</TD></TR></TABLE>

Well I'm not sure anyone here said that stoich was when the engine burned all the fuel. But the 15.4:1 was more of what I was looking for not too unreasonable.

Now as far as running open loop, well it sounds like a good idea but the ecu does not monitor the O2 which is all fine if your tuning is on point as you say it is. But if the ems you ran was more adaptable with a wideband then why not let the computer do the work? Not every load situation is forseeable.

 

I idle around 15 - 15.5. I don't go as high as 16 because that's when the engine starts to hesitate. At about 16.5 the engine shuts off.

 

Ive been able to adjust the afr during cruise conditions to 16.5:1 without any problems. Over that it gets a little bit of surge that could be annoying if it was driven very far. 18:1 it starts to buck/misfire.

 

mine wont go much past 14.5 at idle with out hesitating.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Enzo Speed &raquo;</TD></TR><TR><TD CLASS="quote">I idle around 15 - 15.5. I don't go as high as 16 because that's when the engine starts to hesitate. At about 16.5 the engine shuts off.</TD></TR></TABLE>

Is this the stock ignition system? and what ems?
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eric@HorsepowerFreaks &raquo;</TD></TR><TR><TD CLASS="quote">mine wont go much past 14.5 at idle with out hesitating.</TD></TR></TABLE>

That can't be right 14.5?? What size injectorrs?? and can I assume your are running an aem ems since you're selling them?



Modified by tommytoes at 9:19 PM 7/30/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tommytoes &raquo;</TD></TR><TR><TD CLASS="quote">

Is this the stock ignition system? and what ems?

</TD></TR></TABLE>


Stock ignition w/ Uberdata.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tommytoes &raquo;</TD></TR><TR><TD CLASS="quote">Is this the stock ignition system? and what ems?


That can't be right 14.5?? What size injectorrs?? and can I assume your are running an aem ems since you're selling them?

Modified by tommytoes at 9:19 PM 7/30/2006</TD></TR></TABLE>

I drive a 1st gen neon...I run SDS EFI. I have 1000cc Injectors.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eric@HorsepowerFreaks &raquo;</TD></TR><TR><TD CLASS="quote">

I drive a 1st gen neon...I run SDS EFI. I have 1000cc Injectors.</TD></TR></TABLE>

I thought your response would besomething along those lines... with injectors that flow that much you can only decrease the duty cycle but so much.....

What do you prefer by the way sds efi or aem ems??

 

AEM EMS over SDS anyday of the week. the sds is a very cheap VERY limited EFI system.

thats like comparing apples to...well...like peas.

I really like the Hydra EMS and the AEM unit...they are very similar so...go figure.

My IDC's with the SDS oscillate from 0%-1% while idling.

 

Stoich (correctly called the stoichiometric mixture) is the theoretical mixture ratio at which all of the fuel molecules will have the exact amount of oxygen needed to combust and no more. At stoich, if combustion were perfect, the only thing coming out of the tailpipe would be CO2 and H2O. You'll commonly see stoich being quoted as being 14.7:1 but this is only an estimate. The exact stoichiometric mixture for the fuel you are using depends on what that fuel is made of. Stoich for 91 octane street gasoline is not the same as for 100 octane race gas. In reality though, it is close enough for purpose of discussion.

Emissions will be lowest close to stoich. NOx shoots up dramatically as the mixture gets leaner than 14.7:1 and that is one reason automakers don't go leaner than that. However, at idle where there is very little load on the engine and combustion temperatures and pressure are not high the production of NOx is not a concern. When load on the engine is increased NOx levels will increase (with lean mixtures).

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
Now after looking into several "afr" labeled post on HT I realize that not too many guys on here will on here will go beyond a 15:1 afr at idle or cruise. Now granted that many newer lean burn engines that run ratios of 22:1 have very powerful ignition systems and some use GDI, I can't see it being too unreasonable for one of the honda's on this board to sucessfully run 16:1 without "major" mods.

Now the only plausible reason for running an afr like this would be to save gas while idling or cruising on the highway but who wouldn't want a few extra miles out of their gallon? Theoretically this wouldn't hurt your horsepower at all either except at idle or cruise, keep in mind that the average car requires about 12-14 hp to keep it at cruising speed.

</TD></TR></TABLE>

Production cars don't 'toggle' around a 14.7:1 stoich. They toggle at something lower, about 14.5:1. The reason for this is the fact that NOx increases so dramatically when the mixture is leaner than stoich that they would rather err on the rich side and produce more CO or HC because they are easier to clean-up. The air-fuel mixture will typically toggle +/- .2 around this 14.5:1 mark so that the leanest the mixture will get is about 14.7:1.

There isn't any reason to try to go leaner than stoich at idle because the difference in fuel consumption of say 14.7:1 and 15.7:1 is so insignificant that you would never notice it at the pump. Depending on engine design you are more likely to have chances of misfires.

At cruise leaner mixtures may get you more gas mileage but it can also cause other issues. 'Transient' response can be poor. This is when you step on the gas to go from cruising to accelerating. If you were cruising at 16.5:1 and you womped on the gas to accelerate and the ECU was programmed to provide a 13.5 mixture on accel you would have to jump 3 air fuel ratios richer to get the engine moving. If you were cruising at 14.5:1 you would only have to jump 1 air fuel ratio richer and are less likely to have transient response issues.

Automakers use EGR (and other methods) to increase fuel mileage by displacing the air fuel mixture in the combustion chamber with inert (albeit very hot) exhaust gases. This works great if executed correctly but too much EGR can cause misfires.

The biggest factor on what air fuel ratio you will be able to cruise at is combustion chamber design (this includes the top of the pistion). Stock components were designed with fuel economy and emissions in mind. When you start putting performance parts in the engine you may not be able to run as lean because the combustion chamber may suck too much heat out of the mixture.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Eric@HorsepowerFreaks &raquo;</TD></TR><TR><TD CLASS="quote">AEM EMS over SDS anyday of the week. the sds is a very cheap VERY limited EFI system.

My IDC's with the SDS oscillate from 0%-1% while idling.</TD></TR></TABLE>

Yeah I downloaded the aem ems software and the number of parameters you can alter is simply amazing, especially the ability to add calibrate or exchange sensor ,like adding a crank trigger wheel and cam trigger wheel in place of the two in the dizzy....Maybe one day I'll be able to afford it....

BTW my aem ems fund is at about $30.00 right now...slowly but surely..

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Scott_Tucker &raquo;</TD></TR><TR><TD CLASS="quote">

Production cars don't 'toggle' around a 14.7:1 stoich. They toggle at something lower, about 14.5:1. The reason for this is the fact that NOx increases so dramatically when the mixture is leaner than stoich that they would rather err on the rich side and produce more CO or HC because they are easier to clean-up. The air-fuel mixture will typically toggle +/- .2 around this 14.5:1 mark so that the leanest the mixture will get is about 14.7:1.
</TD></TR></TABLE>

Actually...Cars equiped with narrowbands and three way catalytic converters (most all)don't really sit around at a specific afr... They will go back and forth from rich to lean usually anywhere from once(older cars) to 20 times per second.....It's called crosscounting ...it can be thought of as a game of cat and mouse between the O2 sensor reading and the short term fuel trim. The purpose of this is for emissions alone...
Because once the cat is warm enough to function it needs to fluctuate slightly between rich (higher CO) to reduce NOx and lean (higher O2) to oxidize HC an CO.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Scott_Tucker &raquo;</TD></TR><TR><TD CLASS="quote">
Automakers use EGR (and other methods) to increase fuel mileage by displacing the air fuel mixture in the combustion chamber with inert (albeit very hot) exhaust gases. This works great if executed correctly but too much EGR can cause misfires.

</TD></TR></TABLE>

And actually the egr was not originally intended to increase mileage but to reduce NOx keep in mind that the egr system was introduced in the 70s before the addition of rhodium as a stripping catalyst to strip the nitrogen atoms from NOx to create N2 . But you are correct that too much of the inert "gas" or at the wrong times will create a density misfire.