Air/Fuel ratio, is there a quick answer? Options

[malcolm2]

OK, I have been tinkering with the new-to-me AFM on my 1911cc engine all weekend. I have adjusted the spring about 20 teeth CCW to get to this point.

I have been using an A/F sensor and gauge. can someone tell me, or direct me to a chart/table of what A/F I should be shooting for on my daily driver.

The last adjustment of the CO screw has left me here:

I have always had a strange idle situation, so lets ignore that for now. any normal adjustments to reduce the idle at normal operating temp eventually stall the car. A problem for another post. (IMG:style_emoticons/default/blink.gif)

the idle is high.... at 1200 the A/F is a smooth 12.2.

I found a long hill and drove up it at about 3800 rpm and the A/F was 12.5.

thoughts?

[jim_hoyland]

Got this from one of Chris Foley's posts

in A:F ratio, you want to see:

13.5-12.9 on the gauge while accelerating or climbing,

12.8-12.5 at WOT,

and 16-17 while cruising, going downhill or decelerating.

Right now I am in those ranges with FI. A little richer on WOT as I can get to 11.5 at times. But seems to run well in these ranges.

[malcolm2]

Great. I get to drive to work tomorrow (no rain). So I will do some documenting. Thanks.

[jim_hoyland]

My experience ( before and after the top end rebuild and new TB) is 12-13 idling in the am; constant cruising speed 14-15.5; up hills it richens a bit.
I used the innovative as the AFR for 3 years; just removed it though.

[pbanders]

Agree with the ranges in Jim's posts for varying load conditions.

[ottox914]

Getting idle and AFR can be a challenge. As the engine warms up, things expand, adjustments can change, seals seal better. In tuning the ITB's on my car, I find that it liked around 12:5 or less at idle. If you open the throttles slowly, the afr would take a dive just as the throttle plates opened, and came back to a more expected level just after that. Listen to your engine, give it what it wants. The guidelines are just that- expected guidelines. Let the motor tell you what it wants to run best, and do that.

[PlaysWithCars]

Peak power is made around 13.5:1, idle is usually smooth at that level as well. You can run leaner at cruise for fuel economy especially if you have load sensing for timing advance (vacuum advance or programmable system). You can get as lean as 15s if you can advance timing enough, but be sure your system will retard and richen as soon as you put a load on it or detonation and eventual damage will occur.

[Mark Henry]

I don't like to see much higher than 13:1 in an iron cylinder engine, my nickies engine I can easily run 14:1 no problem.
I can really see the performance degrade as the temps go up in a iron cylinder engine if you run much over 13:1, the nickies equipped engines doesn't suffer from this issue.

Deceleration it doesn't matter...no load.
I have a fuel cut below a certain TPS setting so on decel my meter goes off the scale.
Fuel cut stops popping and/or backfiring on decel on wild cam engines.

plays with cars I'll have to say you are wrong, those number might be fine on a watercooled car, but aircooled always needs to be a bit on the rich side.
Trying for those numbers on an aircooled and you will hole a piston.

Big issue on a performance, wild cam, ITB Type 4 is your vacuum signal will be total shit. This gives the MAP sensor a horrid signal that peeps chase forever, often blaming the FI system.
I run TPS/O2 only program on my T4 2600cc engine, zero issues, runs on par with a modern FI car.

[timothy_nd28]

(IMG:style_emoticons/default/agree.gif) Aircooled engines may need to run slightly more rich than the water coolers

[Keith914]

When in doubt, do the spark plug color test.

[Mark Henry]

When in doubt, do the spark plug color test.

I still do this time to time as a control, but a proper working O2 wideband meter will be spot on.

I tune both FI and carbs with a wideband, they're so cheap now anyone who tunes their own engine should have one. (IMG:style_emoticons/default/shades.gif)

[porschetub]

Doing final tune on my Zeniths,dropping idles down a touch as well as mains,I always run a little fat on the jets with any aircooled engine.
I don't really trust plug colour to much with the modern fuel.
Mark what is the best performing/value AFR kit to use?,would like to install one,the 911 engine is a hungry beast on carbs would like to get that the best I can.

[malcolm2]

Help me out with WOT. I played with that a little at lunch today.

How do you test that? I was running in third gear about 45 mph. I floored the pedal. The car picked up speed and the gauge dropped to 10-ish and the car accelerated.

I only held the pedal down for about 15 seconds. Was not sure I was doing it right.

How and how long?

[Mark Henry]

Mark what is the best performing/value AFR kit to use?,would like to install one,the 911 engine is a hungry beast on carbs would like to get that the best I can.

You want one with the biggest LED numbers, a tiny dial or numbers are hard to read on the fly.

I'm not sure what's best now, my O2 WB is a WMS that I bought 10+ years ago and has been solid as a rock. They stopped making them because they couldn't compete against the cheap china made units, it cost $500 back then. It's small but has 1.25 tall LED numbers.

I've heard good things about the PLX and if you're a techie they have a bluetooth for your phone or tab. Like my WMS it has datalogging, but with the bluetooth option you can do this right on your phone.
But there's also a real cheap one on evilbay for $135

Beware of the $80 Inovate "deal" on evil bay, it doesn't have the lambda sensor... the most expensive part.

[timothy_nd28]

I think it would be a cool gauge to have. Would it be better to have it as part of the car or a tool in your toolbox?

[porschetub]

Mark what is the best performing/value AFR kit to use?,would like to install one,the 911 engine is a hungry beast on carbs would like to get that the best I can.

You want one with the biggest LED numbers, a tiny dial or numbers are hard to read on the fly.

I'm not sure what's best now, my O2 WB is a WMS that I bought 10+ years ago and has been solid as a rock. They stopped making them because they couldn't compete against the cheap china made units, it cost $500 back then. It's small but has 1.25 tall LED numbers.

I've heard good things about the PLX and if you're a techie they have a bluetooth for your phone or tab. Like my WMS it has datalogging, but with the bluetooth option you can do this right on your phone.
But there's also a real cheap one on evilbay for $135

Beware of the $80 Inovate "deal" on evil bay, it doesn't have the lambda sensor... the most expensive part.

Thanks have somewhere to go now, (IMG:style_emoticons/default/beer.gif)

[Mark Henry]

I think it would be a cool gauge to have. Would it be better to have it as part of the car or a tool in your toolbox?

Yes I do this all the time BUT for some odd reason the lambda doesn't like to be removed and reinstalled many times. After it has been in several cars they tend to fail. They also seize in place, but using an anti seize paste they often don't ground properly.
Believe me at $80-$100 a pop I'm damn careful removing and installing them, but they still fail.
Leave it alone and they will last 100K+ miles. If it's dedicated to the one car leave it installed on the car.
Aftermarket FI you have to have a O2 sensor for the computer.

[Porschef]

It's a great tool to have, especially if you're going to start messing with the AFM. I picked up an Innovate, from eBay, almost 4 years ago. Works fine. My car runs well, but cold start up requires a foot on the throttle for 30-60 seconds, depending on temp.

Hope to get it on a lift within a month for a good valve adjustment and some push rod tube seal replacement... (IMG:style_emoticons/default/dry.gif)

[McMark]

Peak power is made around 13.5:1, ....

That's theoretically ideal. But if you want to drive your car in the real world, you need to forget about theoretical. Or at least pay more attention to what the engine is telling you. No dyno-graph in the history of cars had peak power at 13.5:1. Ever.

When in doubt, do the spark plug color test.

I've heard reading spark plugs was more accurate on older fuels. Supposedly new fuels don't indicate as well on the spark plug. I don't have any real world experience to share in this department though. I look at them, I 'read' them, but I don't trust it much.

Help me out with WOT. I played with that a little at lunch today.

How do you test that? I was running in third gear about 45 mph. I floored the pedal. The car picked up speed and the gauge dropped to 10-ish and the car accelerated.

I only held the pedal down for about 15 seconds. Was not sure I was doing it right.

How and how long?

You want to hold WOT and see how things respond. So it's one of those annoying answers -- hold it long enough to learn what you need to know. 15s should tell you all you need to know though. You want to see AFR go rich as soon as you hit the gas and stay rich while at WOT. You want something in the neighborhood of 12:1. 15-16 at cruise will give you great fuel economy, but may be a little lean in my experience.

[ConeDodger]

Peak power is made around 13.5:1, ....

That's theoretically ideal. But if you want to drive your car in the real world, you need to forget about theoretical. Or at least pay more attention to what the engine is telling you. No dyno-graph in the history of cars had peak power at 13.5:1. Ever.

When in doubt, do the spark plug color test.

I've heard reading spark plugs was more accurate on older fuels. Supposedly new fuels don't indicate as well on the spark plug. I don't have any real world experience to share in this department though. I look at them, I 'read' them, but I don't trust it much.

Help me out with WOT. I played with that a little at lunch today.

How do you test that? I was running in third gear about 45 mph. I floored the pedal. The car picked up speed and the gauge dropped to 10-ish and the car accelerated.

I only held the pedal down for about 15 seconds. Was not sure I was doing it right.

How and how long?

You want to hold WOT and see how things respond. So it's one of those annoying answers -- hold it long enough to learn what you need to know. 15s should tell you all you need to know though. You want to see AFR go rich as soon as you hit the gas and stay rich while at WOT. You want something in the neighborhood of 12:1. 15-16 at cruise will give you great fuel economy, but may be a little lean in my experience.

Reading spark plugs became outdated with unleaded fuels. Mark, you never really lived with leaded fuel so... (IMG:style_emoticons/default/biggrin.gif)