Air/Fuel ratio, is there a quick answer? |
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Air/Fuel ratio, is there a quick answer? |
malcolm2 |
Feb 5 2017, 05:50 PM
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#1
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Advanced Member Group: Members Posts: 2,745 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
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? |
McMark |
Feb 7 2017, 11:31 AM
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#2
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
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. 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.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? |
ConeDodger |
Feb 7 2017, 11:46 AM
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#3
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Apex killer! Group: Members Posts: 23,596 Joined: 31-December 04 From: Tahoe Area Member No.: 3,380 Region Association: Northern California |
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. 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.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? Reading spark plugs became outdated with unleaded fuels. Mark, you never really lived with leaded fuel so... (IMG:style_emoticons/default/biggrin.gif) |
Mark Henry |
Feb 7 2017, 12:05 PM
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#4
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
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. 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.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? Reading spark plugs became outdated with unleaded fuels. Mark, you never really lived with leaded fuel so... (IMG:style_emoticons/default/biggrin.gif) Not totally and it also helps when looking for mechanical issues. You are still looking for a greyish or brown tan colour and oil fouling and too lean still looks the same. I use the plug check when I suspect the sensor may be failing. Way too lean or rich I don't need a meter to tell me that the engine is running like shit, but it sure makes life easier. But on top of the WB meter you should have a head temp gauge, if you do try to lean the engine for cruise you will see your head temps climb like crazy when you go too far. |
malcolm2 |
Feb 7 2017, 02:18 PM
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#5
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Advanced Member Group: Members Posts: 2,745 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
But on top of the WB meter you should have a head temp gauge, if you do try to lean the engine for cruise you will see your head temps climb like crazy when you go too far. Yesterday, travelling the same route I always travel, I noticed that my CHT was slightly higher than it had been. Higher that is, when I was on the interstate, about 70 mph, going up a long hill. The normal reading was slightly below 350. I was slightly above 350. so maybe 15 - 20 *F higher. The AFR was reading 12.5-ish. So I would be concerned if I needed to set the AFR at 15-16 while cruising at 70mph. |
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