Can someone explain air/fuel ratio? - Vintage Mustang Forums
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post #1 of 21 (permalink) Old 06-06-2019, 10:15 PM Thread Starter
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Can someone explain air/fuel ratio?

Hello everyone..

My new 66 has an aftermarket gauge package that has an air/fuel ratio gauge. It read 14.6 pretty much all the time. What is the importance of that, what does 14.6 represent, and what does it mean if it changes?

Thanks for explaining to a new guy!


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post #2 of 21 (permalink) Old 06-06-2019, 10:28 PM
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https://x-engineer.org/automotive-en...e-performance/

in theory at 14.6 you are almost spot on to complete combustion ,in practical terms you are probably a little on the lean side especially at WOT at higher RPM


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Last edited by 2nd 66; 06-06-2019 at 10:33 PM.
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post #3 of 21 (permalink) Old 06-07-2019, 12:58 AM
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14.6 parts of air to 1 part of fuel is what it means. It is a principle of chemistry called stochiometry meaning that is an ideal ratio for the most complete combustion. Works really well at idle or part throttle cruise under no load but it needs to be a higher ratio (lower numerically) like 12 or 13 to 1 probably as the engine comes under load, and if carbureted the accelerator pump will richen the mix temporarily. Fun stuff and still works amazingly well after all these years.

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post #4 of 21 (permalink) Old 06-07-2019, 10:46 AM
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Technically speaking, it is not air, but oxygen. In a perfect scenario, 14.7 parts of oxygen are required for 1 part of gasoline to achieve optimal combustion. However, due to variations in cylinder head design and intake manifold design, the optimal AFR at WOT throttle is generally around 12.8:1.

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post #5 of 21 (permalink) Old 06-07-2019, 11:30 AM Thread Starter
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Pretty cool stuff.. thanks for the explanation and the link..

I could be a little lean, I’ll have to watch it and see what it does.. usually I’m watching where I’m pointed, especially when accelerating..

The PO admitting tuning wasn’t his forte’.. I’m bringing to my guy next week, might need a tweak or two.

Thanks!
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post #6 of 21 (permalink) Old 06-09-2019, 10:10 AM
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I'm jealous, I would love to have one but have not had the discretionary income to add one. I never see them used anywhere. If you are interested in learning about your carb (especially if you have a Holley Carb which is tuneable in every way) and are into advanced tuning, they are the Bomb! If not, they are bling, cool bling but nun-the-less bling.



MOst cool people look down on people that have them, you should definitely take it off and sell it to me ;o)))
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post #7 of 21 (permalink) Old 06-09-2019, 11:06 PM
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Quote:
Originally Posted by dobrostang View Post
I'm jealous, I would love to have one but have not had the discretionary income to add one. I never see them used anywhere. If you are interested in learning about your carb (especially if you have a Holley Carb which is tuneable in every way) and are into advanced tuning, they are the Bomb! If not, they are bling, cool bling but nun-the-less bling.



MOst cool people look down on people that have them, you should definitely take it off and sell it to me ;o)))
I'd like one too, Perhaps not to the degree of a gasket below the fuel level()Holley. But, Edelbrock carbs are tune able also. I have a feeling My new engine might be lean up top. Rumor has it @Huskinhano has one now,He might need to keep an eye on it at the next Rat Pack Reunion
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post #8 of 21 (permalink) Old 06-10-2019, 07:03 AM
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My brother bought me for Xmas. It’s interesting to see what’s going on. Since you say it stays a steady 14.6, to me that sounds like you have EFI? My short experience with mine is that it’s all over. It moves with the gas pedal. My carb seems to be a bit rich, typically I’m around 12.5. In 4th gear it’s a steadier 13.8. I guess I should go through my yard shed carb and rebuild it alone with leaning it out a smidge.
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post #9 of 21 (permalink) Old 06-10-2019, 07:18 AM
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That actually sounds more real-world for a carb'd engine. Almost no time is a carb is gonna run 14.6 exactly, especially for any length of time, due to their nature and changing road/ load conditions, and some performance cams require a little richer mixture to smooth out idle. I use the STOP / SOTP tuning method ... Spin Tires on Pavement / Seat of The Pants...
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'66 Tahoe Turquoise/ Aqua coupe
•289 / 4100 •C4 Auto •Disc Brakes
•Dual Exhaust •16:1 Manual Steering
•Rally Pac •Console •Deluxe Belts
•LOTS of Rotunda accessories
•Original Styled Steel Wheels
...my first car

'66 Emberglo / Parchment coupe
•289 / 2100 •C4 Auto •Disc Brakes
•Dual Exhaust •16:1 Power Steering
•Dealer Air Conditioning •Console
...son's first car


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post #10 of 21 (permalink) Old 06-10-2019, 11:44 PM Thread Starter
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Thanks guys.. yeah, somethings not right as it stays fairly steady 14.6, with just a flicker up or down. I’m running a Holley 570 street avenger, hmm... I just realized the manual choke isn’t hooked up..

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post #11 of 21 (permalink) Old 06-11-2019, 03:38 AM
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Perhaps it's not connected to the sensor, or the sensor is bad? If it's not moving, there's bound to be something wrong there. It would at least give you different readings when the engine's cold vs. hot, or idle vs. winging the throttle. Has to. No carb ever built can maintain the same A/F ratio under all driving conditions, without a little variance.
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post #12 of 21 (permalink) Old 06-11-2019, 08:15 AM
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If it says 14.6 all the time, it’s broken. Lol
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post #13 of 21 (permalink) Old 06-11-2019, 11:51 AM
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Quote:
Originally Posted by FTWingRiders View Post
Thanks guys.. yeah, somethings not right as it stays fairly steady 14.6, with just a flicker up or down. I’m running a Holley 570 street avenger, hmm... I just realized the manual choke isn’t hooked up..
You should check at where in the stream it is installed and look more into how that matters. You can pull the sensor out and read it almost like a spark plug.
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post #14 of 21 (permalink) Old 06-11-2019, 12:43 PM
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Teflon tape on the threads?

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post #15 of 21 (permalink) Old 06-11-2019, 01:28 PM
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My JBA H pipe has a bung on each side. I am only using one side as had I planned better I find there are gauges that accept two inputs. Anyway, the AFR gauge in the photo has been relocated to a 2 gauge panel that is magnetically attached to the bottom of the dash on the passenger side. Its removable for shows and the wire plug is easily hidden. I am thinking I might like a sweep type reading over the digits as sometimes it changes so fast its hard to read.


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