Air/Fuel Meter/gauge
 

This has been mentioned lately and I'm interested, but completely ignorant about it. When we get past about the mid 80s, cars got a lot of stuff I don't know about.

I googled this, mostly what I found was 2 or 3 hundred dollar gauges to install. I'm guessing there must be a version for shop testing? Looks like you weld a bung in your exhaust, is this always required?

Anyway, I'd just like a little practical information about this with our old cars. Thanks!

Re: Air/Fuel Meter/gauge
 

yes, you need a bung in the exhaust---then a "oxygen sensor" gets screwd

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I have a "sniffer" on the short exhaust pipes on the engine on my engine test stand. It is a tube welded to a "C"-clamp that clamps to the exhaust pipe that the sensor screws into. It's a relatively common way to temporarily mount an exhaust sensor to an engine.

Re: Air/Fuel Meter/gauge
 

I nave the weld in bung on my 33 .34 and 28 A, an easy way to het the mixture right. we use an inovate setup .
Lawrie

Re: Air/Fuel Meter/gauge
 

Back in the "Day" we could read the plugs, the new gad deleted that? Yes It's a better way to get thepower and cruise ratios right. I tune all my engines for economy, but you have to make sure the engine doesn't go lean on power. It takes a good ignition system to get both.

Re: Air/Fuel Meter/gauge
 

I have a A/F gauge in my coupe. They're very easy to install, but you need a welder or a buddy that will weld in the bung for you. For a blown motor, it's crucial to have the right air/fuel mix

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Do you need two for dual exhaust?...should they be close to the engine... Thanks.... Mark

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There is a specified distance to locate the sensor from the ex valve for the best readings. Not sure how critical it is, but with a turbo (the installations I am most familiar with) they what the bung located in specific locations.

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It's best to follow the manufactures specs. They all ask for something a little different.
Only one is needed.

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Another thing about a "sniffer" is that it can be moved from one pipe to the other if you are running duals. It may not be quite as accurate as a properly placed bung, but you can check both sides with one gauge.

Re: Air/Fuel Meter/gauge
 

Its the only way to see what your air fuel ratio is under any driving condition. Even if you do not plan to buy a A/F meter now if your building your exhaust system weld a bung in so you will have it for later.

These on not the old fashioned "oxygen sensors" which generated a .1 to 1.0 voltage. The computer used the voltage reading to switch the exhaust from rich to lean (extremely fast) so the catalytic converter could work properly. The A/F ratio needs to be switching above and below to .5V reading from the oxygen sensor. This gives a 14.7:1 A/F ratio for a three-way catalytic converter to work. These new air fuel ratio sensors are sensing the actual A/F ratio. This is an incredible tool for tuning an engine.

New cars can use up to four of these sensors. One on each bank of a V8 engine as close to engine as possible and one after each of the catalytic converters. This is how the computer knows the catalytic converter is still working. If the oxygen readings are the same before and after the catalytic converter it is no longer working.

You do not need two sensors, just one for dialing in your air fuel mixture. Two are used for the computer to test the catalytic converter and to compare one side of the engine to the other (bank 1 and bank 2). You only need two if you are diagnosing a problem such as an engine misfire, vacuum leak, injector problem or mechanical issue. The computer also uses the the separate sensors to adjust the A/F ratio (injector on time) for each side on the engine but that can only be done with port fuel injection. You just need one sensor for what we do. You could install a bung on each side so if you do have an engine problem you can swap the sensor between the two sides. All that will do is tell you which bank the problem is on. You can do the same thing by pulling individual plug wires and watching the rpm drop.

We had the sniffer on the smog machine along with the dyno but you cannot simulate a real world load on the vehicle unless your driving it.

Install a A/F gauge and a vacuum gauge in you car and you will learn a lot from watching the readings.

When you get the timing and A/F ratio dialed in there is still a little known trick for adding one more horsepower to your Flathead. You don't even need a dyno to detect it.

Re: Air/Fuel Meter/gauge
 

When Richar Kunc was doing all his research on the ignition system. He picked me up at the airport in his 53 Ford HT with the 276, L-100 engine. The af meter was right in front of me. On the 60 mile trip back to his house, the meter was in the lo to mid 15's and hi 12's on accelerating. 22 mpg. That's what you can do with the right "Stuff"

Re: Air/Fuel Meter/gauge
 

Thanks!!!.....Mark

Re: Air/Fuel Meter/gauge
 

I can't say I understand much yet.....but I will. No problem putting bungs into pipes. If I could just get the Hudson Hornet off our lift I could work under my Ford again.

Re: Air/Fuel Meter/gauge
 

Those are good readings. You will hear people always quote 14.7:1 as being the preferred ratio. That is the exact ratio to make the catalytic converter work correctly and still let the engine run decent. Without a catalytic converter we can do better than that. 12:1 is perfect performance air fuel ratio and 15:1 is perfect for maximum fuel mileage. We had Dodge vehicles with carbs at work that ran 16:1, that was a little too lean. They always felt like they were right on the verge of a lean misfire. Your friends '53 Ford'd flathead is dialed in, you can't get any better than that. The air fuel gauge is such a neat tool. I will never build another car without one.

Re: Air/Fuel Meter/gauge
 

Here is a video so you can see one of the these gauges working while selecting the correct main jets. You can read the comments about the video and see how many different opinions there are selecting air fuel ratios.

https://www.youtube.com/watch?v=2DYLhJ4hhx0

Re: Air/Fuel Meter/gauge
 

Something about those gauges doesn't look like 6 volts to me.

Thanks for the youtube link.

Re: Air/Fuel Meter/gauge
 

Seeing that you are limited to a 6 volt system is different story.
The AFR gage is really only needed to set up the carb.
But if you truly want to use a gage then it can be installed and used with a small stand alone 12 volt battery such as the many 'jump-pack' batteries that are available.
Using stand alone battery eliminates any polarity concerns.

Re: Air/Fuel Meter/gauge
 

Also, you might be able to use something like this to boost the 6V to 12V. I use a similar product on my tach drivers and they work quite well/ Polarity is also a concern.

https://www.amazon.com/eBoot-Convert...11-spons&psc=1

Re: Air/Fuel Meter/gauge
 

One of the reasons the opinions vary WIDELY on what the A/F should be set to is the variances between different meters. There is also the fact that differing engine systems can dictate the requirement for different mixtures. I have tested several brands of A/F meters under the same conditions and found that the owner should plan to experiment beyond what the meter is indicating.

Re: Air/Fuel Meter/gauge
 

Some of the “tuning” involves making the engine run right, not just satisfying the meter,..... correct?.....Mark

Re: Air/Fuel Meter/gauge
 

I installed an Innovate AFM on my truck, used it to tune my Holley 94. Decided I was done with it, so I sold it. Then I switched to a Rochester 2G, so I bought another one. There is about a 1.0 difference between the two units. Interestingly, both show 12.5:1 when the PV's are clearly open.

My engine runs like crap if I try to get above 13:1 at or just above idle. I've read where some get their engines to show 14's at idle, just not in the cards for mine. The difference in gas consumption just can't be significant, the difference in driveability is huge.

Re: Air/Fuel Meter/gauge
 

Trying to achieve those readings at idle seems like too lean to me.
What are your cruise speed readings?

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At a steady cruise, 45+, mid-to-high 14's. I could do better but I live at 5300' altitude, but have jets that allow me to get down to the lowlands without hitting 17's. Also, pushing a truck thru the air takes a lot more HP at cruise than a smoother car. The drag coefficient for a '52 is about the same as a barn door.

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Ya' I can see where altitude change could present a problem.
Would be nice to adapt an aircraft carb. with variable mixture control on the dash but those are for the most part, up draft carbs.

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Then you need the instrumentation to adjust it!

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Not on the ones I had, just a mixture control on the instrument panel to adjust for altitude.

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That is interesting, so you adjust it by ear? Everything I have flown had EGT gauges at least.

Re: Air/Fuel Meter/gauge
 

I am in mid-central Minnesota at a bit above 1000' elevation. I have an AEM gauge on my test stand. From experience, while a flathead will run at the desired 14-15:1 at speed, they tend to idle best at about 10:1. I consider it to be normal, and have convinced myself to live with it.

Re: Air/Fuel Meter/gauge
 

A lean mixture needs more advance in cruise, and there only distributor that can providing that is the SBC along with the right advance under pow.. It get kinda tricky balancing this timing with the AF/ I start with 16 mechanical all in by 2k and 8 degs Vac I use the initial , just to get it started. This way you have aprox 26/28 degs in cruise, and 18/20 at WOT. Which will prevent detination on tje crapy gas we have. Haveing an adjustable Mach advance also helps. This might sound like allot of work, but the 5 plusK invested in the engine is worth it.

Re: Air/Fuel Meter/gauge
 

Thanks for the great information!

Re: Air/Fuel Meter/gauge
 

Question for all flathead AF experts. Is it possible to tap into the exhaust heat riser crossover on the intake manifold to insert an AF sensor? Would the readings be useful?

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It seems to me I read in another post here on the barn that they need to be like 24" away (Down stream) from the exhaust port of the engine???

Re: Air/Fuel Meter/gauge
 

Chat GPT says the sensor should be within 18" of the exhaust port and after any mixing of exhaust ports. With dual exhaust you can get the four sensors of either bank. If it goes in the heat riser you get exhaust from the center two cylinders of both banks. That might be better. What I wonder about is the fact that the sensor would not be in a steady exhaust stream but a back and forth exhaust flow.


I am not going to do any such experiment, but would love to hear the results if some other flathead fanatic tried it.

Re: Air/Fuel Meter/gauge
 

For several years I have had an Innovate 02 sensor in one of their exhaust clamps and the extension wiring to go from the back of a vehicle up to the driver's area. I install the O2 gauge and a vacuum gauge both in an under dash mount and added a wiring harness that can be powered either by a cigarette lighter port or by alligator clips on a 12V battery. I assembled this to be a portable setup that is easily moveable from vehicle to vehicle. I find I don't use it much, like Ross related, once a vehicle is tuned and running well there is no longer a need for an O2 gauge. I got it out last weekend when I switched to a larger throat carburetor on my 53 sedan and needed to verify I wasn't running lean.

After testing lots of flathead era Fords over the years I have concluded that the Ford engineers knew what they were doing and there is no need for an O2 meter if you have a stock engine in good condition. You only need an O2 meter if you are doing something "off label".

Picture is the gauges showing 12.1 : 1 ratio and 21 inches of vacuum at idle.
https://fordbarn.com/forum/attachmen...1&d=1718274179

Re: Air/Fuel Meter/gauge
 

Good points made but I would also add that generally its best to tune to what the engine is telling you it wants and not to a specific "number" on the gauge.


For example, on a street type engine, I will pull fuel at part throttle/cruise till the engine surges slightly then add fuel till it goes away, regardless of what the gauge says. The carb idle circuit rolls into the transition circuit on most carbs as well, including 97s.



The engine is telling you where its happy at cruise where there is low load anyway.


Then I'll use the PV circuit to dial in the AFR for WOT.


At idle I'll go lean/clean (within reason to avoid overheating) but keep in mind that there is no load on the engine at idle so idling in the mid 15s won't hurt, just keep an eye on temps and adjust accordingly.


This approach has worked for me from 600 cube Hemis to our flatheads.


Right now I'm dialling in 4x97s on a Weiand WC4D on a fresh 283 SBC (gasp), and arriving at the idle, jetting and PV combo has been easy with basic changes.



Every engine is different and the best thing about using the AFR gauge is it will tell you the effect of tuning changes more quickly and save a lot of time.

Re: Air/Fuel Meter/gauge
 

Sure miss him..
G