Air/Fuel Meter/gauge

[flatford8]

Originally Posted by JWL

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.

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

[Ross F-1]

Originally Posted by JWL

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.

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.

Originally Posted by flatford8

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

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.

[51 MERC-CT]

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

[Ross F-1]

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.

[51 MERC-CT]

Originally Posted by Ross F-1

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.

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.

[JSeery]

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Originally Posted by 51 MERC-CT

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.

Then you need the instrumentation to adjust it!

[51 MERC-CT]

Originally Posted by JSeery

Then you need the instrumentation to adjust it!

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

[JSeery]

Originally Posted by 51 MERC-CT

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

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

[tubman]

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.

[Ol' Ron]

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.

[jeepguy1948]

Thanks for the great information!

[drolston]

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?

[rockfla]

Originally Posted by drolston

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?

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???

[drolston]

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.

[38 coupe]

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.

[Blownflatheaddeuce]

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.

[Ol' Ron]

Sure miss him..
G