what size carb for a 416 stroker

Fuel and Air Systems

  1. northeastmopar

    northeastmopar Well-Known Member

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    Currently running a holley avenger 770. Holley website says I should be running an 870 cfm carb on a mild 416 stroker motor. My issue is that at idle my car seems to be running real rich when I smell the eye burning exhaust. Once I am underway it seems to clean itself up. I was thinking that maybe the 770 is not providing enough air flow at idle which is causing it to run rich. I have edelbrock aluminum heads with a performer airgap intake.
     
  2. SGBARRACUDA

    SGBARRACUDA ROY FABO Gold Member

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    I have Indybrock heads on my 416 68 Barracuda with a Cam Motion 246/250 solid roller and 3.91 gears with a Dynamic 4200 stall convertor. I'm running a Holley 750HP on it that seems to be a good fit for this combo. I also have a 950 HP to try on it but I like the way this 750 HP performs on it.
     
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    • 416stroker

      416stroker Well-Known Member

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      I'm running a 780DP on mine. Had to dink with the idle circuit a bit to lean it out at idle. Not unusual for a Holley to be rich out of the box. Picked up the Holley work book which helped a lot when making changes.
       
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      • northeastmopar

        northeastmopar Well-Known Member

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        I talked to Holley. I picked up a small power valve than came with my carb. I think they advised I go from a 7 to a 5? Have not installed it yet.
         
      • mopowers

        mopowers Well-Known Member

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        Sounds like your current carburetor just needs to be tuned. A different power valve isn't going to do anything for the idle circuit.
         
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        • CudaCraig

          CudaCraig FABO Gold Member FABO Gold Member

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          Electronic fuel injection . Give her the beans
           
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          • northeastmopar

            northeastmopar Well-Known Member

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            Ya, I bought a vacuum gauge. I just need to learn how to proceed from start to finish to adjust/tune the carb. That is where I wanted to go, but I find sound bites and not a good start to finish approach?
             
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            • mderoy340

              mderoy340 Well-Known Member

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              • j par

                j par Well-hung Member

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                Innovative wideband O2 sensori will help and looking at the plugs...
                Make adjustments accordingly...
                Not just smell...
                 
              • rumblefish360

                rumblefish360 So close, yet so far away FABO Gold Member

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                FWIW, I would be looking at a HP series Holley or the like from another seller of carbs. The Avenger series carb has a lot of complaints. This may be due to inexperienced hands. I don’t know.

                As far as carb size goes, I think we’re all missing a little bit of info. In post #2, Roy gives his combo. Also, what is your primary use of the car? If it is mostly street, I’d run a slightly smaller carb and not worry about that last few HP on top I’m leaving up top in favor of the increased throttle response that makes driving the car pleasant and responsive.
                 
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                • AJ/FormS

                  AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                  Burn your eyes exhaust is in the tune.
                  Your throttle blades are possibly/probably too far closed, and your idle trimmers to far open. Your engine is wanting more Idle-bypass air.

                  I don't know that for sure cuz I don't know anything about your build. But every single time, without exception, when I run into burning eyes, it's because the timing is too far advanced, the throttle has been closed too far, to keep the idle speed down, and sometimes the PCV is not there.

                  Forget idle tuning with a vacuum gauge, it doesn't work on a big-cammed V8. Know this, your stroker, at idle, will like achitload of timing; that don't make it right. It might like 20,30,35, even 40 or more degrees. And it shows it by idling faster and faster. So what do you do? You close the throttle...... which simultaneously closes BOTH air and fuel. So the engine wants to stall. What do you do? You crank out the mixture screws, and when that stops working, you say to yourself what? You say your carb is too small it can't supply enough idle fuel!, Am I right?
                  But the real culprit is the too much advance and the subsequent too small throttle opening, which has shut off your primary low-speed fuel circuit,namely the transfer-slots. Get your transfer slots back on line, and let the idle timing be what it will be. Then adjust your rate of advance to come in as fast as possible, without detonating, by your stall speed. Your engine does not care about power-timing below stall speed, because it never has to pull hard down there, so forget about the numbers. Just find out how much timing she wants by stall-speed, and give it to her. If your stall speed is below 3600, then your power-timing with aluminum heads is gonna want to be 32/34 degrees by 3200/3600. As a streeter it does not have to be perfect from the get-go, because it's a flipping stroker which annihilates the tires in first gear no matter how crappy slow the timing is.
                  Say your stall-speed is 2800. And say by trial and error you determine that 30* by 2800 produces detonation, but 28* does not. So now you have a data point. Your second data point is 32/34 by 3200, so you crank it up to 34* and that does not detonate after 3600, but does at 3200, What do you do? Well you can't run the 34 until it no longer detonates, so continue testing and the magic silence comes at 32* at 3400 so there is your next data point.
                  Say your idle timing ends up not stinking at 800rpm with 16* so that is another data point. Plot the points on graph-paper with rpm across the bottom from left to right, and degrees of advance vertically up the left side. Now, subtract two degrees from the higher two points, and plot the numbers on the graph, and connect the dots Finally build your D to match the graph as closely as possible.
                  This gives you a 2-degree safety net for final tuning.
                  Now go out and get your fueling and heat-range dialed in.
                  Then revisit the timing.
                  Btw, as a streeter you are gonna hate that 5.0PV. It won't open until the gas pedal is on the floor. That means you have to run a bigger than necessary MJ so you have some driveability. Cuz most of the time you will not be at WOT,lol. So what you really need to do is engage the PV earlier, so you can downsize the MJ.
                  My little 750DP/230* cammed 367 likes a 10.5. This makes for a smooth power-delivery, with less reliance on the pumpshot. I don't know what your stroker might need, I haven't tuned one, but I suspect it will like it. This is one place you can use your new vacuum gauge........ if you want to. Just plumb it to manifold vacuum, and stick on the windshield where you can see it. Then off for a roadtest. Get her into second gear at above stall. Then slam the pedal down to about 8" vacuum and watch the needle. What you want to see is a smoothly rising needle keeping pace with the tach, with no flat spot, or hesitation, or stumble. The needle must never go backwards or stop rising until maybe 18 to 22 inches; watch your speed. This is not a power test, rather driveability. So try it at various speeds and pedal applications, always dropping the vacuum to slightly below the 10.5 cut-in point. Also try just tipping into it right on the 10.5. If you have an AFR gauge, let it help you. But I find that the no-stumble/no hesitation rule works just as well. Do this AFTER the timing curve has been bugged out. I go to 8 inches so that by 10 the pumpshot has been used up. Watch your speed.
                  After you get the PV on line, you may be surprised to find that you can take a lot of pump-shot out.
                  And we haven't even talked about Vacuum-advance.

                  Almost any carb can be tuned to idle on almost any V8 P-car engine, including a SuperSix tiny 2bbl, to an 850, the biggest I have tuned.
                  If your idle trimmers are opened to more than 50% of their working range, chances are very good that the throttle blades are too far closed.
                   
                  Last edited: Dec 26, 2019
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                  • Oldmanmopar

                    Oldmanmopar Going left turning right FABO Gold Member

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                    i ran a 1050 quik-fuel they have a chart for this. Our air fuel was perfect through the quarter with dual rich lean guages. @14. 416 @ 8000 calls for a 1050. That was through the exhaust.
                     
                  • yellow rose

                    yellow rose Doctor of Thinkology.

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                    That is exactly ASS BACKWARDS and piss on Holley for telling you that idiotic crap.

                    If you are fat at idle, you can open the idle air bleed up (this is why any carb without changeable brass is worthless) or you can make the idle feed restriction smaller, or both if you need to.

                    You set your cruise air/fuel ratio on the primary main jets and you set your wide open throttle air/fuel ratio with the power valve channel restrictors. Those are the holes behind the power valve.

                    You set power valve timing (opening point) using cruise vacuum and NOT IDLE vacuum. This is wrong, has always been wrong and will always be wrong and is one of the major reasons guys with a Holley or Holley clone can't get the tune up correct.

                    FABO member 12many has a thread on this forum (I think this forum...it could be another forum...maybe someone can find that thread and link it here) where he correctly set his power valve timing and then fixed the rest of his tune up and had exellent results. That thread SHOULD be a sticky.

                    I'd fix what you have if you can. Brass and drill bits are cheaper than a carb, and whatever carb you buy, unless you buy a custom tuned carb will need the same things done to it.

                    Shame on Holley for telling their customers ignorant tuning advice. Shame on all the authors who propagate this crap.

                    And yes, I get a case of the ass every time is see guys having issues like this. It's just dumb that Holley and the idiot book writers won't admit their mistakes and correct them. Pisses me off.
                     
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                    • yellow rose

                      yellow rose Doctor of Thinkology.

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                      This is a good place to start learning as a quick reading by me shows he is setting the power valve timing from cruise vacuum. That says a lot. I'd expect most everything else in there to be real c,one of not dead on.
                       
                    • yellow rose

                      yellow rose Doctor of Thinkology.

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                      The O2 sensor can fib, and will. Read the plugs first and then use the O2 sensor.
                       
                    • 12many

                      12many Well-Known Member

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                      I can admit it was only a short while ago that I sucked at tuning carbs, primarily Holleys where I just fiddled with settings on the outside of the carb, tuning with a flat blade screwdriver essentially. Maybe change some jets here and there.I had a lazy and good enough mindset for the most part. To the unfamiliar, less experienced or apprehensive when it comes to carb tuning: I’ve learned over the years there is no such thing as a “turn key” or “bolt on and go” carburetor. Forget that mindset. The only bolt-on and go carb is a “by coincidence” carb imo. You have to learn the circuits, and fine tune them. Think “whittle it down” circuit by circuit, get a tuning book and learn how the thing works. Get an a/f gauge, helps get things in the ballpark quickly, along with doing plug readings you can dial it in.
                       
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                      • rumblefish360

                        rumblefish360 So close, yet so far away FABO Gold Member

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                        Where is that thread by 12many?
                         
                      • MobileCustoms

                        MobileCustoms Well-Known Member

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                        • yellow rose

                          yellow rose Doctor of Thinkology.

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                          • MobileCustoms

                            MobileCustoms Well-Known Member

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                            I looked it up because I still need to address my own setup and remembered reading that thread before but forgot where it was! Now it's back on my radar...
                             
                          • K.O. SWINGER

                            K.O. SWINGER Well-Known Member

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                            How about a round 1000 CFM. Sorry I couldn't help myself
                             
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                            • K.O. SWINGER

                              K.O. SWINGER Well-Known Member

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                              Screenshot_2019-12-27-08-44-56.png How about around 1000 CFM sorry I couldn't help myself
                               
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                              • 72Dart6pack

                                72Dart6pack Well-Known Member

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                                Same. I went with these carbs. :)

                                IMG_25071 (1).jpg
                                 
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                                • K.O. SWINGER

                                  K.O. SWINGER Well-Known Member

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                                • K.O. SWINGER

                                  K.O. SWINGER Well-Known Member

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                                  But for real Roy your motor sounds like a beast!
                                   
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