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Technical Air/ Fuel Ratio Gauge Installation

Discussion in 'The Hokey Ass Message Board' started by jaw22w, Mar 12, 2021.

  1. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,300

    jaw22w
    Member
    from Indiana

    A couple days ago, I ordered an air fuel ratio gauge for my old coupe. I thought I might be able to coax a few more MPG's out of the old girl. Besides, I'm bored and need something to play with. It should be here today. So, I spent pretty much all day yesterday researching air/fuel ratio gauges. I'm starting to think that wasn't a smart move. There are so many different opinions on where to put the 02 sensor. I have read anywhere from 14" to 40" downstream. Some say that the closer installation keeps the carbon burnt off the sensor. ???? If I put the sensor in the end of the header, it would be about 20 inches
    downstream. I don't really want to do that because you will see the sensor and the wires going to it. I would rather put it in the vertical section of the bypass to the muffler system, on the inside towards the apron. Then I could wire it through the backside of the apron and never see it. That would put it about 26" downstream. They all say to put the sensor in the top half of the pipe to avoid pooling condensation. Installing it in a vertical section should take care of this problem. Sound like that will work?
    Any of you guys have experience with this? Any tips or help is appreciated.
     
  2. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,300

    jaw22w
    Member
    from Indiana

    IMG_0758.JPG
    Here is a pic.
     
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  3. I have never installed one- but your theory sounds good- condensation won’t ‘pool’ as they say in a vertical section of pipe-but getting the engine to operating temp should take care of any condensation in the system anyway.
     
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  4. Joe H
    Joined: Feb 10, 2008
    Posts: 1,096

    Joe H
    Member

    Mine is installed at about 2 o-clock in the pipe some 30" or so from the closes exhaust valve. This is on a inline six with stock manifold. I have a gauge from Speedhut https://www.speedhut.com/gauge/GL-AFWB-01/7/Air-Fuel-Gauge-Wide-Band-10-18-(FOR-INNOVATE) , the instructions say you can mount to O2s on a stick or pole and shove it into the tail pipe for testing multiple cars or trucks, so the actual mounting of the bung in the pipe may not be all the critical. Mine reads perfect all the time once the sensor and exhaust heat up. I went from 14 to 21 mpg on the highway by changing metering rods.
     
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  5. Truck64
    Joined: Oct 18, 2015
    Posts: 5,074

    Truck64
    Member
    from Ioway

    I bet it would work fine in the vertical section. But I don't know for a fact. There can't be any air leaks, there is at least the potential for one, after that junction.

    But there's nothing that says you need to leave it hooked up on a constant basis. In fact one characteristic of the sensor itself is they must be powered anytime the engine is running or they will be "fouled" permanently.

    If you want another gauge to watch all the time that might be what you want. I just used it for carb calibration or tuning purposes and removed everything.

    I can see if you bought the dash type gauge that would be something else.
     
  6. Like a lot of things involving our rods, it's easy to overthink things.
    Your idea sounds reasonable. Do it.
    Worse case is you later have a better idea. We all redo things a second or third time. Keep posting your progress and results here.
     
  7. COCONUTS
    Joined: May 5, 2015
    Posts: 1,017

    COCONUTS

    I work at a Datsun dealership setting up new cars, while in school. They had a O2 sensor (stand alone machine) that I would stick in the tail pipe for the reading. The machine had a gauge with a piece of thin red tape marking the spot I needed to reach when setting the carburetor so that it would not run to rich or to lean.
     
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  8. squirrel
    Joined: Sep 23, 2004
    Posts: 49,789

    squirrel
    Member

    if you're going to leave it in the car all the time, put the O2 sensor in the pipe under the apron. If you plan to just play with it for a little while, then put a plug in the threaded bung, you could probably put it closer to the engine somewhere. With the exhaust setup you have, it will look quite out of place, no matter where you put it, if it's out in the open.

    Some cars just really don't want to have an O2 sensor on them...I'd never put one on my Chevy II, for example.
     
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  9. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 1,198

    wheeltramp brian
    Member

    Very helpful tool.i put one in my dd 64 elky.383/700r4 3.55 gears.qjet carb.got the idle,full throttle,and part throttle cruise tuned in perfect.went from 14 to 20 mpg on the highway!and it ran good before just super rich.who knew till you know the numbers!
     
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  10. Truck64
    Joined: Oct 18, 2015
    Posts: 5,074

    Truck64
    Member
    from Ioway

    ^^ That was my experience. Plugs stay clean and crisp too, no combustion chamber carbon buildup, washing out rings & cylinders, diluting crankcase oil, etc.
     
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  11. squirrel
    Joined: Sep 23, 2004
    Posts: 49,789

    squirrel
    Member

    I put one on the 57 one ton I had, which had a mild 454 with a Q jet on it. The numbers read like it was EFI....with an old stock carb, rebuilt to stock specs.

    So yeah, you can see what's going on. On the other hand, you might see that you did a good job of tuning, without the gauge.
     
  12. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,330

    sunbeam
    Member

    With Duals you will only see 1/2 of the cylinders but you will see both sides of the carb. Has anyone run 2 to compare the sides?
     
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  13. RmK57
    Joined: Dec 31, 2008
    Posts: 1,903

    RmK57
    Member

    Mine is towards the end of the header collector. One of the best mods you can do IMO. With a Holley 950 hp on a BBF I went from a 11.5 - 12.5 a/f at light cruise to part throttle to a nice 15-16 a/f with air bleed, idle feed restrictors and other mods. That would be around 30% better fuel economy.
     
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  14. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,300

    jaw22w
    Member
    from Indiana

    I bought an Autometer to match my vacuum gauge. They will reside next to each other on the steering column. They will both be permanent. I love gauges. You can't have too many.
    I think I can hide the sensor in between the pipe and the apron so that it will at least not be a thumb in your eye. I can wire it from underneath, just a hole and grommet in the apron. You'd have to be inspecting to see it. I'm thinking that I need to put a little angle on the bung so the sensor is downhill a little into the pipe also to stop any puddling in the sensor.
    This is in my '26 T coupe. MPG's are going to be severely limited by the frontal area of this car anyway. It's like pushing a whole sheet of plywood down the road. I just rebuilt the Goodwrench 350 that is in it. Threw away everything but the block and crank. Bored .030, decked, balanced. 10:1 CR Promaxx aluminum heads, custom cam, etc., etc. I am using the same carb, QFT SL 600 VS modified to 4 corner idle, so I know it's going to need at least some fine tuning. And I figured that the A/F gauge might help improve my skills.
     
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  15. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,510

    2OLD2FAST
    Member
    from illinois

    Post converter downstream sensors are mounted in the side of horizontal exhaust pipes without problems .
     
  16. Dyno Dave
    Joined: Feb 18, 2011
    Posts: 291

    Dyno Dave
    Member

    I'm considering a air/fuel gauge installation in my '54 Chevy Bel Air, going from the original 235 to 270 in. 261, decked block & head, Howard's lumpy cam, long tube headers and Corvette 3 carb sidedrafts. Has a c.r. Camaro 5 speed to a 4.10 geared S-10 posi rear end. I'm being told to bump the jetting 10%, then run it and pull the plugs for a reading. My thinking is that this approach would be doable for a flat out full thottle pass, mine is a street car and I don't have the knowledge to read the plugs, and the car been down for several years, and I "wana drive it"soon !!! How would this +10% thing give you your entry and mid-range plug readings... needed for street use. I would use a 2 band unit, one probe into each header. Info Please, Thanks, dyno dave
     
    Last edited: Mar 28, 2021
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  17. Truck64
    Joined: Oct 18, 2015
    Posts: 5,074

    Truck64
    Member
    from Ioway

    Basic routine is to have the engine in good proper running shape - you're all done with tune-up, timing, ignition curve, ignition, vacuum advance, everything is squared away. Fuel pump, float height, and fuel bowl level is very important. Then tune each carb circuit individually.

    Set your idle where it runs good and idles smooth. Don't try for a specific number on the AFR meter. It will need re-adjustment seasonally anyway. As lean as it can be while still running smooth would be what you want, to avoid fouled plugs.

    Then set your cruise jetting AFR, that is, running steady in high gear on flat ground highway (part throttle) for a good clean economical cruise. Most stock or stockish carbureted engines with a proper ignition and timing curve run very happily into the high 15s or more. Jet down until you find a "lean surge" or misfire. Then jet back up 2 sizes.

    Then be sure to fatten up the full throttle and acceleration AFR, if required. Different carb makes have different strategies or components for the power circuit but it's all the same thing. Don't go lean under load, power or acceleration. About 12.5 AFR or so is safe.

    You'll hear stuff about "stoich" or stoichiometric and perfect ratios, but these are theoretical and never really seen at idle, cruise or acceleration. Don't chase the numbers, just use the AFR gauge to verify and confirm what you can already hear and feel. Keep inspecting the plugs regularly, you'll notice big changes in the AFR won't really show big changes on the plugs necessarily. It's pretty hard to read plugs with modern gasoline, but with an AFR gauge you won't have to grenade your motor to learn.
     
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  18. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,300

    jaw22w
    Member
    from Indiana


    Thanks for that. I have been looking for a tutorial on using the AFR gauge. I am finding a lot of instructions on how to install the gauge and bung, but not a whole lot on tuning with it. Anybody got a good write-up or video on AFR tuning? I am tuning on a QFT SL-600-VS which has changeable jets, idle feed restrictors, and air bleeds. It would be nice to find AFR tuning info specific to the QFT 600, but that is probably asking too much.
    I got the engine running last night with a new ignition system and the new AFR gauge. I got the ignition curve set up (16 initial + 18 mechanical)and the idle mixture screws all adjusted. Sitting in the shop idling the AFR is reading about 14. So the idle is probably not far off. I haven't driven it yet, but I will bet the cruise, acceleration, and WOT are going to show rich. It was raining last night so I will take it out this morning after the roads dry up and see how the rest of the system is. I have a good range of jets and a few different power valves. I just bought a range of IFR's and air bleeds so I have them if I need them. I love to tinker and experiment, so this ought to be fun.
     
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  19. Joe H
    Joined: Feb 10, 2008
    Posts: 1,096

    Joe H
    Member

    I run dual Carter W-1 carburetors on a 250 inline six. To tune them, I made a couple runs down the highway to see what readings I was getting. I then went around town watching the gauge. Mine was rich all across the driving range.
    The W-1s have three step metering rods, off idle, mid range, and full throttle. Jets are also available. I was able to find metering rods with leaner off idle and midrange diameters and richer full throttle tips. To get the last little bit of tuning I needed, I adjusted the floats. Fuel level makes a big difference just off idle where the vacuum is high.
    Mine runs around 15.6 - 16.5 on level ground @ 65 mph, it will go higher in the right conditions. At full throttle it runs around 13.0 : 1. Everyday is different, and every season is different, so tune for the weather you mostly drive in and don't worry when the weather changes and the readings are off.
    I didn't see much change in readings when messing with the timing. I use cheap 87 octane with 10% ethanol, don't know what readings I would get with different fuel.
     
  20. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,094

    ekimneirbo
    Member
    from Brooks Ky

    I would put it underneath just inside the frame rail if there is room. If its cluttered with things like brake and/or clutch paraphenalia, then try the passenger side. As long as it has a slight downward tilt it should be fine. You want it reasonably close to the hotter exhaust, but remember that Detroit also used O2 sensors in the pipe AFTER it went thru a catalytic converter and they worked fine. Definitely agree that you don't want it visible from the outside of the car, so thats about as close as you could install one.;)

    Remember also that you want to keep track of the adjustments that you make just in case you need to revert to them later. The O2 sensor is only going to average what is coming from 4 separate cylinders that have different intake runner lengths. The end cylinders usually run a little leaner than the center ones, so you don't want to get too lean on any cylinder while adjusting the average. Modern fuel injected vehicles usually have replicated intake tracts that are very similar in shape and length.........and then the appropriate amont of fuel is squirted directly at the intake valve completely atomized and with the proper ratio. Carbs and different length intake passages along with fuel coming out of suspension and forming droplets presents a different scenario. The O2 sensor should be a useful guage, but I'm just suggesting that it may be more limited in its accuracy, so take that into account when trying to lean things out. I do think its a good idea because it definitely should tell you if things are way out of kilter. I think they can also be very helpful for initially dialing in new carbs.
     
    Last edited: Mar 27, 2021
  21. Truck64
    Joined: Oct 18, 2015
    Posts: 5,074

    Truck64
    Member
    from Ioway

    Yeah, but I don't think the post-cat sensors were used for AFR reading though were they? They just decided if the catalyst was lunched, or not

    The O2 sensors will really show the tuner how changing something, anything, affects tuning and sometimes in a big way. Plug heat range, float height, idle mixture screws, jetting, vacuum advance, etc.

    Also keep in mind what works fine for flatlanders won't work well at higher elevations. It's one thing to drive over the hill in a few hours, but if you live at high elevations jetting and power circuits should be corrected for. The key or metric you're looking at basically is engine vacuum. Power circuits are based on manifold vacuum, and it is reduced as elevation increases. Camshaft plays a big role too. If you live at a high altitude a big ole' heap a helpin' camshaft advance is welcome, too.

    Short answer: lean it out till it squeeks on the highway, though make damn sure it's good & fat under power and load.
     
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  22. speedshifter
    Joined: Mar 3, 2008
    Posts: 279

    speedshifter
    Member

    jaw22w, I believe you will find your A/F gauge very valuable. One surprise is how much most hot rod air cleaners change the A/F ratio. On my car the sensor is way beyond 40" down stream. Gauge appears to be completely accurate, Greg White
     
  23. If you think about it whatever comes out of the engine goes all the way out to the end of the tail pipe. And if anybody's ever noticed it's still pretty hot when it comes out. It would make sense that it doesn't really matter where you put it it probably will work just fine.
     
  24. Joe Travers
    Joined: Mar 21, 2021
    Posts: 417

    Joe Travers
    Member
    from Louisiana

    Was considering A/F gauge installation myself for easier carb tuning but that tuning is still variable due to temperature, humidity, altitude and barometric changes. Only way to tune to variable conditions is EFI. I keep it old-school. Read the spark plugs. ;)

    Joe
     
    Last edited: Mar 27, 2021
  25. Dyno Dave
    Joined: Feb 18, 2011
    Posts: 291

    Dyno Dave
    Member

    I was hoping for some comments on the usefullness of a A/F gauge as a short-cut to get the idle, mid-range & wide-open throttle mixture settings. As mentioned I'm running 3 Carter sidedraft 1BLS. and would replace metering rods & jets as needed. They are available (Corvair) thru Blackhawk Engineering. The information about Innovate Motorsports # 3891 dual band unit shows usage on V8s & V6s, mine is two inline long tube headers.
    Shouldn't this unit still work ??? Thanks, dyno dave
     
    Last edited: Mar 27, 2021
  26. Truck64
    Joined: Oct 18, 2015
    Posts: 5,074

    Truck64
    Member
    from Ioway

    Sorry I wasted my time and experience trying to help you. Promise, I won't do that again.
     
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  27. Dyno Dave
    Joined: Feb 18, 2011
    Posts: 291

    Dyno Dave
    Member

    Truck64, there's a misunderstanding here! Got a lot of A/F information from your posts. Obviously my intent wasn't made clear, with my limited knowledge level in this area, just seeking some reassurance that getting and installing this gauge package could be a quicker way to get the '54 up and running... Your advice is very much appreciated.
    Thank You dyno dave
     
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  28. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 2,094

    ekimneirbo
    Member
    from Brooks Ky

    Perhaps this is something that might help............

     
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  29. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,300

    jaw22w
    Member
    from Indiana

    Thanks. I hadn't seen that one. I watched it. Then another, then another.... That lead to about all afternoon watching you tube videos, so I didn't get much done. I did learn a few things. Thanks again, I think. We'll put the lack of progress down to education.:):rolleyes:
     
  30. Once you get it all figured out you can teach the rest of us. Thanks.
     
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