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Discussion Starter #1
So, curious to know what other have experienced with an O2 sensor (wideband AFR gauge) on the classics (65-68)
I have a 302/4 speed top loader/Tri-Y's/ and will be installing just after the collector on the passenger bank. I purchased the (AEM 30-0300 kit)
- I'm curious to know how/where others have installed, what experience they had using the gauge to adjust the carb etc...

photos, written descriptions, opinions, all welcome..
 

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I was thinking of doing that myself a while back. But I had a series of problems with my OE carburetor due to my use of E10 fuel slowly dissolving the metal. So instead of buying an aftermarket carburetor and tuning it like I had planned I just went with a fuel injection system. It self-tunes based on the wide band O2 sensor that came with the kit.
 

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If you are serious about understanding and properly adjusting a carb a wideband system will be needed. I bought the NGK AFX system almost exactly 4 years ago (March 2013) and could now never live without one. I have had it on three different cars/engines and it works equally well on all of them although its mounted in different locations on each. A slightly modified Camry drain plug makes a perfect blank plug when you remove the O2 sensor from a pipe to move it to a different car.

Your word 'collector' must mean you have headers? I don't. On the '66 GT I mounted the sensor in the H-pipe just a few inches behind the right exhaust manifold where it was easy to access for installation/removal. For the '66 coupe its in the single exhaust pipe under the back seat and the wire comes in under the back seat. For the '39 Rolls its even further back behind the rear axle. The AFX has about a 10' long hook up cable so you can easily put it in any of those locations and then swap it around between different cars. As long as you are not close to the open tail pipe end it doesn't really make much difference where you mount it unless you are concerned about one half of the exhaust (left vs right bank V8, etc.) measuring different than the other. I think the rule they quoted was more than 20(?) exhaust pipe diameters from the end.

It took me months to learn how to read the gauge much of which was 'unlearning' what little I thought I knew about carbs and AFR. Much of what is posted out there in forum-land is fiction. At the time, I thought that exhaust gas temperature would also be useful so I also have an EGT system I built that fits in a similar bung. Although EGT is interesting it tells you next to nothing compared to a wideband AFR. EGT is a lot cheaper since I used a $50 high-temp thermocouple from Grainger for EGT which can be read using the standard thermocouple connection on a $20 Sears DVM. The special thermocouple wire connectors cost more than did the DVM. I now rarely even look at EGT even when I have it installed. A more useful measurement is a temperature sensor (0-200F) installed inside your air cleaner telling you how hot the air is going into the engine. That helps explain why you have carb problems on a really hot summer day.

I have used mine for two Autolites, a 2100 and a 4100, and an English Stromberg designed much like, just larger than, the Stromberg '97 used on 1930s Ford V8s. The AFR meter works the same for any of them but it helps you understand the carb design and how they work...or don't work very well. As an engineer I always end up plotting my data for analysis. An example of that is the first attached plot for an Autolite 2100. That is AFR measured in top gear (third for a C4) at steady road speed (neither speeding up or slowing down) taken on flat pavement vs three different main jet sizes. The speed axis should really be the volume of air volume passing through the carb but that is difficult to measure; road speed is a lot easier. You can't easily maintain a constant speed in high gear below 15-20 MPH on a public highway which is why there is no data closer to idle. The data was also taken 5,000' above sea level so it may look different than yours.

What you learn from that kind of a plot is that any idle screw adjustment you make change almost nothing except at idle. You can tweak the idle AFR to 12, 13, whatever. Once you crack the throttle open even a tiny amount to move the car slowly the AFR will drop to 11. Idle screws only make the engine idle smoothly, nothing else. Then as you slowly build speed the AFR continuously leans out because of how the transition circuit is designed which has nothing much to do with either idle adjustment or main jets. Once you get enough speed, i.e. air flow gets high enough, you transition to the main jet circuit for cruising. Once in cruise the main jet size in an Autolite is what determines AFR for any speed until your power valve opens. Up to 80 there is no power valve for steady speeds so the plot shows nothing about how AFR drops to 12-13 when you floor the pedal.

In contrast, the second plot is similar data but for a pre-WWII designed Stromberg. This design is grossly inferior to the later Autolite and never flattens out into a true cruise region. The faster you drive, the leaner the mixture gets until the power valve opens and drops you back into the 13s. The power valve here is opened by an adjustable, mechanical linkage to the throttle shaft. To pick the correct main jet for this carb you have to first know how fast you are going to be driving.
 

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The digital readouts on the meters may look nice but its not at all useful when trying to visually read the meter. Those last digits will change so quickly in random directions as you drive down the road that you find they become meaningless. The AFX display is only digital so I quickly added an analog meter to the system making it easier to read meaningful numbers. You can easily average a moving needle to take a reading accurate to 0.1 AFR. You can't come even close to that using a randomly varying digital display. Only if you log the data and analyze later on your computer will the digital data be useful. An AFR meter is a digital computer running complex software so the data comes out digital to begin with. Its just that's humans weren't designed to read digital readouts that are rapidly varying.

You will also find that all the work you put into 'accurately' adjusting your carb were probably wasted since when the temperature, weather, etc., changes your AFR will also change. One of the good things about the Autolite design is that the AFR in the cruise mode is fairly stable WRT those changing conditions. Not that there is no temperature variation since you will find that the optimum main jets for an Autolite are different for summer vs winter because of the big temperature difference. You will also find that your engine seems to run pretty good with quite a wide range of jets. That is how Ford, or any other maker, could get away with specifying a single size jet for use year round. Only with an AFR meter can you tell the difference.
 

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Discussion Starter #5 (Edited)
Thanks Guys for the replies.. It helps me build an expected base line of expectation with reading others experience.. the car runs pretty well now, but I HATE not knowing exactly what's going on. I expect the changes to vary with temp in seasonal changes same as a choke, intake etc. but having hard data is nice as it simplifies the guessing game and i DON'T read plugs. That's a lost art. I know enough to know if they are Too Too lean or just fouled but when you get into using a magnifying glass to see if there are tiny metal flake spots down in the groove of a spark plug to determine how it's running, I'm out. The AEM gauge I bought has a function to allow you to choose how many digits after the decimal you want showing on top of the color code reading, but really I'll just plot points based on my three stages of output 1) idle, 2) cruise at 40,50,60,75 and lastly 3) WOT. from there I can choose my rod and jets accordingly. Being I live in phoenix, the temp stays pretty average here and is not extreme so there is not as much big changes required.. you can get away with leaving it if your not competing. Mine is just a cruiser/toy.
 
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