40 degrees initial!

Small Block Mopar Engine

  1. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    It's like something is goofy. Both of my v8's would die out if they were timed at 40° initial. very few engines will. The old drag racers would hook the distributor 12 volt power to a toggle switch and crank it over to start it and switch on the ignition so it wouldn't kick back against the starter. Unless you have a 350° duration .700 lift cam you don't need that.
     
  2. JG1966

    JG1966 Well-Known Member

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    Thanks Mike. Just to be clear, I never moved throttle above idle while at 40* initial. I moved it right back to 20* initial. Never drove it like that or even touched throttle manually. I was stunned to see it there, too. I'm gonna check my springs (per Rusty) and see if I have some issue that's causing it to "want" 40 initial. It certainly didn't die out, so based on your experience something must be up. I'll leave timing at 20 initial, 38 total for now (I know she runs well at that) and then do those carb tests to see if I'm way too lean at idle.
     
  3. AJ/FormS

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

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    IMO, What you experienced is normal.
    At Idle, the engine wants far more timing than we can ever give it. By 2000 no load she could be wanting mid to high 40s an mine likes up to 60 by 2240.
    But you cannot, at idle give her what she wants because, to keep the idle speed down with a typical carb, the butterflies want to dip under the transfer slots. So in response you have to increase fueling from another source, like the mixture screws. So then, you can make it idle on the ragged edge of having the transfer slots very nearly closed. When you do this, the transfers start pulling massive amounts of air around the butterflies, and the fuel flow drops way down. But you can make it idle because the timing has put the max cylinder pressure to the crank at the right time so that it really does not take much fuel to keep her running. So far everything is fine.
    The problem s come when you try to drive away.
    First, when you put it into gear, the sudden load pills the rpm down, and airspeed down, and now there is just barely or maybe not enough fuel ,to sustain running.
    So, you fudge around with it and luck into a setting where it doesn't stall, and then you think you are ready to drive away, but the instant you open the throttle, you get this huge stumble, while the transfers try to wake up. But you finally get thru it, and now the thing is pig-rich cuz the mixture screws are maxed out. So no, with a carburator, you cannot run 40* of idle timing.

    At Idle, timing is dictated by;
    the synchronization of,
    the stumble-free, drive-away point, on the transfers, and the chosen idle speed.
    You first set your mixture screws in the middle of their adjustment range. Then you open the butterflies to a point that exposes the transfer slots underneath them to an amount that eliminates the off-idle stumble, which usually makes them appear to be square to a lil taller than wide. Then you adjust the idle-speed with timing to whatever you want it to be.
    Then you verify that the off-idle tip-in, still works without a hesitation.

    As the cam gets bigger, they want more idle-air than the butterflies can give at this setting, so your job is to find it elsewhere. And when you do, the idle speed will have to be adjusted by changing the timing. Eventually, your mechanical Idle-timing will likely stabilize at 12 to 18degrees. Now your Vcan will work. Yes it will.
    I have,in the past, run a 223/110 cam and currently run a 230/110 cam, both on ported Vcan, both with a 22*maximum. And both with 14* initial.
    BTW, you cannot hurt your engine with 40* of idle-timing, if that is what it took to peak the rpm.Run it up to 2000, and again tug on the D until the rpm peaks, then read the timing at 2000. Do same at 3000.
    The engine is telling you, by the rise in rpm, that it is liking the timing increases. When it slows down, your engine is telling you that,it is no longer liking it.
    But
    You just can't put much of a load on the engine at these numbers, for fear of detonation.
     
    Last edited: Sep 26, 2020
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    • JG1966

      JG1966 Well-Known Member

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      Thanks AJ. I follow most everything you are saying, but how do I add more idle-air when I get to that step? The IABs and/or IFRs?
       
    • AJ/FormS

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

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      The same for you Mike; they should idle at 40*, just not at an rpm low enough because the butterflies end up falling underneath the transfer slots, as you back out the speed screws; so the fuel dries up, and she stalls.
      If your transfer slot exposure is right, you can tug on the Vcan to 30* for sure, and if the rotor phasing stays good, then 40* should not be a problem. You will just end up with a very high idlespeed.
      The opposite is also true. If your T-slot is right, then you will be able to retard the timing, perhaps down to 5*, but the idle rpm will slooow right down. As long as the transfers can keep flowing, and the power circuit doesn't start up, it will happily tic away at 550 or perhaps less depending on your idle-air bypass also working.
      My 367, with the 230/110 cam will still pull itself at 550 rpm on a flat level hard surface; at 5* advance. By 500, I got a lil slip in the clutch. With the Commando 4-speed 500 is 3.6mph/parade speed, with 3.55s.
      This is why I have a hi-volume oilpump,lol. and extra oiling to the topend, and drip holes drilled into the valley between the lifters, and drain-channels ground into my Eddies, etc.
       
    • beanhead

      beanhead Well-Known Member

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      AJ's on it, as usual.. idle is a no-load situation and you can advance the timing more than is desirable for driving. Put it in gear though, and ugh. The 20 you had sounds good, if it idles strong and clean there. Idle timing just needs to be 'enough' and the carb settings take it from there. A problem would be, if you needed 40 degrees just to get it to run right.
       
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      • AJ/FormS

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

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        What are you doing still up?
        Yes you can mess with those and smarter guys than me can take you down that path. If you have a 4-corner idle system, then you can crack the secondaries. Or you can mess with the PCV system. Or I just drill a small hole in each primary butterfly, up between the transfer slot and idle discharge, about 1/3 of the way back to the center. The size of the holes will depend on your cam, and engine size. My 223* cammed 367 liked 5/64. My 230* likes 6/64 , my 292/292/108 found 8/64 a lil much. I had to solder up the holes and start over, with 7/64 . Chamfer the holes on both sides, just enough to remove the burs.

        If you make the holes too big, you will have to add fuel,to smooth her out; and then the idle speed will go up, and then you will have to retard the timing. That's all fine but when you get to under 14*, the low speed tip-in response will start to get sluggish. This is more noticeable with engines of less pressure. Mine has a tic under 180, so not a big deal.
         
      • roccodart440

        roccodart440 Well-Known Member

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        Mine made more power at 36 than 34 on the dyno so it really depends on the engine.

        22/36 in at 2600
         
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        • 318willrun

          318willrun Utube channel 318willrun

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          depends on compression. low compression small blocks can like up to 42*. My 318 Duster now is at 40*, ET slip proven that's where it likes it. ALWAYS let the engine decide, not a pre-determined number on a piece of paper before the build even starts.
           
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          • gregcon

            gregcon Well-Known Member

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            I'd first confirm, as other noted, your damper marks are correct.

            You never said what your CR is...that would be good to know.

            Nothing wrong with 40 degrees at idle as long as you back off of it as soon as you start to load the engine.

            In the late 90's I had a 526" Hemi with an 8-71, Speed-Pro EFI, 8:1 CR, and .420 lobe roller cam. By the time I had the tuning done, the spark map would be at 52 degrees advanced during cruise conditions. It ran super-smooth on the highway, like it had 24 cylinders. Of course, the timing would back off as soon as load increased. I had set up the car to include a knock sensor* but in the end it ran so well I didn't bother.

            The real problem in all this is not the advance but the primitive ways in which we control it (on a non-computerized system). But you can at least try to emulate what a PCM would do.

            *Tell the PCM to take all or most of its timing commands from the knock sensor.....run the advance right up to the point of knock
             
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            • JG1966

              JG1966 Well-Known Member

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              Thanks AJ. I'm a night owl. ;) My carb is an AED 750 and they come with butterfly holes already drilled (nice feature I didn't realize when I bought it), so that's already covered. I would prefer to not have to mess with the IABs and IFRs if I can avoid it. The guys at AED told me unless I really know what I'm doing, that I shouldn't mess with them.
               
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              • fishmens67

                fishmens67 FABO Gold Member FABO Gold Member

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                Very good post :thumbsup:
                 
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                • yellow rose

                  yellow rose Overnight Sensation FABO Gold Member

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                  That’s what they ALL say to make you think they are smart and you are dumb.

                  Take notes, make your changes and then take more notes.

                  All you are doing is changing and drilling cheap brass.
                   
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                  • fishmens67

                    fishmens67 FABO Gold Member FABO Gold Member

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                    I don't need a lesson in power tuning. lol
                    I just through out a number that would surely be a close number, proven.
                     
                  • 318willrun

                    318willrun Utube channel 318willrun

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                    It wasn't for you because you run big blocks anyways, it was for anyone that might not know.....
                     
                  • Hysteric

                    Hysteric Well-Known Member

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                    When an engine wants a lot of timing its lean. When you have low comp and a bigger cam there isn't a lot vaporization taking place before ignition time so burn proceeds slowing.
                     
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                    • Hysteric

                      Hysteric Well-Known Member

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                      What a load of shit. Mess with them and start to see how that affects your cars performance. If it were mine i would rip that 750 off and put a stock holley 650 DP with stock calibration on it. You would probably find that the 650 would run better all round.
                       
                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      You're right. It's all combo dependent.
                       
                    • JG1966

                      JG1966 Well-Known Member

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                      Hey Rusty. I pulled the distributor and, what do you know, both springs had slots. And one of the "eyes" broke -- with barely any pressure -- as I was removing it. So I'm replacing them with two good "full circle" springs. It may not do much as far as my original post, but these springs needed to be replaced either way.
                      20200926_191355.jpg 20200926_191425.jpg
                       
                    • yellow rose

                      yellow rose Overnight Sensation FABO Gold Member

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                      You really need to find someone with a distributor machine and have them set it up for you. @halifaxhops can do it if you want to ship it.

                      You will spend more time trying things than it takes to get it done on a machine.
                       
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                      • JG1966

                        JG1966 Well-Known Member

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                        That's certainly not a bad idea. Thanks.
                         
                      • RustyRatRod

                        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                        Well I'll be dog. The one that's not broken was stretched real bad too. I bet those springs was the problem. Or at least a big part of it.
                         
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                        • RustyRatRod

                          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                          Ray set up the slant distributor I am running in Vixen now. I could tell a nice difference in acceleration, too.
                           
                        • JG1966

                          JG1966 Well-Known Member

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                          I just sent Halifax a message. Turns out we are almost neighbors.
                           
                        • RustyRatRod

                          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                          Well heck yeah! A match made in Mopar heaven.
                           
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