correct air/fuel ratio??
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Thread: correct air/fuel ratio??

  1. #1
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    correct air/fuel ratio??

    I just installed a MSD 6al box on my car. I noticed that the a/f ratio was 12.8 at an idle. At 3000rpm it's in the 13 range. Some time ago, it was 14/7 or so, going down the road at 3000rpm. It is a 355 sbc, 10 to 1 comp, [email protected] & .525 lift, 2 500 Eldebrocks. Am I in the right ballpark with this a/f ratio? Thanks in advance, Rod

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  3. #2
    Senior Member mmhotrod's Avatar
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    Rod I’m no air fuel expert. But I did find this article:

    It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1. This is roughly 13 parts of air to one part fuel.

    sounds to me you did pretty good with your setup. Timing and carbs or even plugs could be a factor.

    https://www.innovatemotorsports.com/...lock-chevy.php
    Last edited by mmhotrod; 10-29-2020 at 11:24 PM.
    Mario





    "I post the work on my hotrod, not because it's the best way, rather it was the way I had to get it done with the resources I had.................
    Of which I might be an encouragement to other hotrodders".

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    Hey, Mario, thanks for the post. I'm glad to hear that I seem to have gotten real close to where it ought to be. I had heard the 14.7 ratio & thought I might have a rich problem. Thanks again, Rod

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  6. #4
    Senior Member mmhotrod's Avatar
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    Quote Originally Posted by raj4851 View Post
    Hey, Mario, thanks for the post. I'm glad to hear that I seem to have gotten real close to where it ought to be. I had heard the 14.7 ratio & thought I might have a rich problem. Thanks again, Rod
    lt seems only the new fuel injection modern style engines can achieve the 14.7 ratio but that’s a clean low emission burn. HOTROD’s just don’t do that with carbueration and tunnel rams. So ya done good Rod.
    Mario





    "I post the work on my hotrod, not because it's the best way, rather it was the way I had to get it done with the resources I had.................
    Of which I might be an encouragement to other hotrodders".

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    Hey Mario, thanks for the thumbs up on my a/f ratio. I have 500cfm Edelbrocks. Do you run 600 Holleys? If so, stock jetting? It seems we may have had a previous conversation about this. I've been threatening to go to Holleys. Maybe someone else on here could jump in too. I'm curious. I've done some research on 50cc squirters, a white cam, and the backfire eliminators(diaphrams I think). Any, not sure but very curious. Thanks in advance, Rod

  8. #6
    Senior Member sbauman2's Avatar
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    Hi Rod

    this is my humble opinion. I originally ran Holley 500 cfm, vacuum secondaries with a balance tube on a crossram on my 53. Click image for larger version. 

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ID:	104259 I did a bunch of changes to the secondary springs til I got them close to where I wanted them to open. I also changed the power valves out. Next came the 50 cc reo pumps and larger shooter nozzles on the primaries that I can't remember the size. I never felt that the motor ran like it should. Off came the 500's and on went the 650 dual feed double pumpers. Click image for larger version. 

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ID:	104261 Conventional wisdom said that a double pumper on a car with an automatic was a no-no. I can tell you they made a hell of a difference. Next was the swap from the crossram to a Ford tunnel wedge manifold and it ran like a different motor. Click image for larger version. 

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ID:	104263 It did however seem fall off a bit after the initial acceleration. I changed all 4 accelerator pumps to the 50 cc reo pumps and swapped the original larger secondary shooters to the primary side and put larger on the secondary side, and what a beast. As for the anti backfire valve it doesn't prevent a backfire it's a check ball that prevents a backfire from blowing out your power valve upon a backfire. At some point Holley started to equip their carbs with them so the kits weren't necessary anymore.
    That's the history for my 53 but it's not a one size fits all type thing. You have to find what works with your motor.
    Last edited by sbauman2; 11-10-2020 at 11:51 PM.
    Steve Hidden Content MOB in sunny So Cal
    "and the beat goes on....................."

  9. #7
    Administrator 1946Austin's Avatar
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    My own experience with my two dual carbed, tunnel ram cars are my Austin with twin 450 cfm Holleys on my 355 SBC, and my '63 Falcon with 464 BBC and twin 1850 600 cfm Holleys with vacuum secondaries.
    On the Austin the 450 cfm Holley carbs have mechanical secondaries, but no secondary accelerator pumps, and that caused huge problems for everyday driving. The gradual transition from primaries to secondaries made a dead spot in the throttle, and the engine nosed over as the secondaries opened. I had to swap in 50cc Reo pumps, and also upsize the squirters a lot to get enough primary shot to overcome the flat spot. But they work now, but still less than perfect. If it wasn't for my Holley Pro Dominator tunnel ram requiring sideways carb mounting, I'd have swapped to the 1850 600's and vacuum secondaries already. This current setup will never be perfect.
    On my Falcon the carbs were 600 cfm 1850's and with the well built 464 BBC engine they were way too lean out of the box. I had surging at lower rpm's, and the engine ran hot too. Mario suggested I was too lean, and when he suggested replacing the stock jets with 78's I did so, and it immediately cured the lean problems. It also made the engine run much cooler, and it never overheated again!
    I had changed the springs in the vacuum secondaries to open sooner, and also had the quick change kit installed, and balance tube to synchronize the openings for the two carbs. It really made a great running engine regardless of whether driving normally, or under full throttle acceleration. Love that setup, and I'd recommend those carbs, and vacuum secondary synchronizing system for almost any street driven car.
    Vall

  10. #8
    Senior Member mmhotrod's Avatar
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    I recommend going Holley too. You can go 650 dbl pmr (more race than street driver) sideways or in line 600’s. With inline 600’s you have the option to go progressive linkage. Progressive will let you tune the rear carb for Normal driving and the front carb can be left at factory jetting and nozzle size. Do you want them to run simultaneously or progressive?
    Mario





    "I post the work on my hotrod, not because it's the best way, rather it was the way I had to get it done with the resources I had.................
    Of which I might be an encouragement to other hotrodders".

  11. #9
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    Hi guys, & thanks for the input. It appears I've got a lot more research to do, along with experimentation. The Edelbrocks have worked well, but there seems to be more options with the Holleys. Thanks again, Rod

  12. #10
    Senior Member mmhotrod's Avatar
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    Edelbrock sells a progressive linkage for your carbs. Have you considered staying with yours and tuning the rear carb for normal driving?
    Mario





    "I post the work on my hotrod, not because it's the best way, rather it was the way I had to get it done with the resources I had.................
    Of which I might be an encouragement to other hotrodders".

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