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  •  » AFR gauge readings

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    7/26/2024 7:20 AM  #1

    Steve69
    Senior 24-7 FYI Addict

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    From: Madison Wisconsin
    Registered: 4/01/2013
    Posts: 2,727

    AFR gauge readings

    Hey there,

    Guys running AFR gauges with your carburetors, what AFR reading are you shooting for?   Looks like 14.7 is the optimal fuel air burn ratio.   I've only adjusted mine at Idle I was at the 14 to 15 range.   Haven't driven it yet and checked it out the AFR.

    Thanks
    Steve69

     

    7/26/2024 7:54 AM  #2

    Raymond_B
    Senior 24-7 FYI Addict

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    From: Fort Worth, TX
    Registered: 4/01/2013
    Posts: 1,184

    Re: AFR gauge readings

    Steve69 wrote:

    Hey there,

    Guys running AFR gauges with your carburetors, what AFR reading are you shooting for?   Looks like 14.7 is the optimal fuel air burn ratio.   I've only adjusted mine at Idle I was at the 14 to 15 range.   Haven't driven it yet and checked it out the AFR.

    Thanks
    Steve69

    There's a lot to that question, but it's probably best to break it down in to roughly 3 areas.

    **Caveat** -- It can vary from engine to engine and combination of parts as well, but here's some generic opinion

    Idle -- on my 427w it liked to idle lean14.7-15ish :1 Big cam, lots of overlap, EFI, etc

    Cruise -- pretty much the same, maybe a tad bit leaner at low throttle position steady state (on freeway doing 65 for example)

    WOT -- Mine was supercharged so I looked for 11.7:1, when it was N/A I ran it in the upper 12's

    Again though, it really can vary. A lot of my tuning was just until the engine was "happy" and then I looked at the numbers.

    I meant to add, this was when it was fully warmed up, cold start and up to 160 degrees was MUCH richer.
     

    Last edited by Raymond_B (7/26/2024 7:56 AM)

     

    7/26/2024 10:56 AM  #3

    Steve69
    Senior 24-7 FYI Addict

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    From: Madison Wisconsin
    Registered: 4/01/2013
    Posts: 2,727

    Re: AFR gauge readings

    Raymond_B wrote:

    Steve69 wrote:

    Hey there,

    Guys running AFR gauges with your carburetors, what AFR reading are you shooting for?   Looks like 14.7 is the optimal fuel air burn ratio.   I've only adjusted mine at Idle I was at the 14 to 15 range.   Haven't driven it yet and checked it out the AFR.

    Thanks
    Steve69

    There's a lot to that question, but it's probably best to break it down in to roughly 3 areas.

    **Caveat** -- It can vary from engine to engine and combination of parts as well, but here's some generic opinion

    Idle -- on my 427w it liked to idle lean14.7-15ish :1 Big cam, lots of overlap, EFI, etc

    Cruise -- pretty much the same, maybe a tad bit leaner at low throttle position steady state (on freeway doing 65 for example)

    WOT -- Mine was supercharged so I looked for 11.7:1, when it was N/A I ran it in the upper 12's

    Again though, it really can vary. A lot of my tuning was just until the engine was "happy" and then I looked at the numbers.

    I meant to add, this was when it was fully warmed up, cold start and up to 160 degrees was MUCH richer.
     

    Thanks for the info!

       •Thread Starter
     

    7/27/2024 5:42 AM  #4

    BobE
    Senior 24-7 FYI Addict

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    From: White Plains, NY
    Registered: 4/04/2013
    Posts: 2,574

    Re: AFR gauge readings

    Here are a couple of websites I've collected on AFR tuning that might be helpful:
    https://www.enginelabs.com/news/video-understanding-your-wideband-o2-sensor/)
     
    (https://innovatemotorsports.com/resources/efi-central.php)
     

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    7/27/2024 6:22 PM  #5

    MS
    Forum Originator

    Offline

    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,172

    Re: AFR gauge readings

    On my 66 427w 750 Holley vac secondary. 
    Idle is easy to get it wherever you want it. Mine idles best a little rich at 14:1.
    At cruise, I need to work on leaning it out, currently 12-13:1
    WOT 10:1
    I gave up on the tune on that carb. It doesn’t want to lean out and doesn’t want to run with 8.5 power valve. Any smaller it leans out.
    I have a new 700 vac secondary Holley with four corner idle circuit to install, so I quit screwing with the 750.   I think it is called LAZY.
    THEN I DECIDED I WOULD DRIVE THE 69 to the Bash, so all my attention is directed towards getting it ready.  It has a 331 and a 600 Holley with 7.5 power valve and 68 primary/72 secondary.  It runs perfect and the car has no A/F gauge, so ignorance is total bliss.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    7/29/2024 8:41 AM  #6

    Steve69
    Senior 24-7 FYI Addict

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    From: Madison Wisconsin
    Registered: 4/01/2013
    Posts: 2,727

    Re: AFR gauge readings

    Thanks, guys, for the info.  I was out of town this last weekend and didn't have time to work on my 69.

    Mine does run great too.  Just trying to figure out the 5-mpg issue. 

    Prior to installing the AFR gauge I was running the engine and I heard this sparking noise on the drivers side that I hadn't heard before.  Two of the plug wires were off.  Prior I was coming home from a car show.  I wasn't with my car 3/4 of the time at the show.  There were a lot of chevy cars there.  Im hoping the plug wires just came off but It had crossed my find maybe someone pulled them at the car show.  I would think somebody wouldn't do that.  It was all highway cruising on the way back and the engine didn't seem any differently.  
    So maybe running 6 cylinders would effect the gas mileage too....LOL

    Thanks
    Steve69

    Last edited by Steve69 (7/29/2024 8:42 AM)

       •Thread Starter
     

     

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