Base timing. Really ?

Electrical and Ignition

  1. A Body 440 WHY NOT

    A Body 440 WHY NOT Well-Known Member

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    I have been reading up on curving my dist on my 440 build.
    10-1
    Alum Toth heads
    530 lift
    248 duration @.050” (296 total)
    109 Lsa
    Holley 800
    Tri y headers .....
    My question is people are talking about 20 degrees ( or so ) of BASE timing. Give or take. It’s a general question. Is this really what some people are running on a warm street engine ? How can that not have a hard start ? From what I am learning the MSD box will knock it back to 20 degrees on start if your over that. Crazy. Just trying to get an idea of what base timing to expect. Pic for attention LoL

    4EF38AF7-1DAE-4646-ACD7-3A6A23099911.jpeg
     
  2. MomsDuster

    MomsDuster FABO Gold Member FABO Gold Member

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    Mine is at 20* no issues at all.
     
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    • DrCharles

      DrCharles Well-Known Member

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      My 451 (currently iron heads, 10.3:1, pump gas), 272@.050 cam, will begin to fight the starter when hot at about 25 degrees. It would start fine at 22-24 degrees but didn't have enough idle vacuum.

      I set up my distributor to crank at 16 and immediately advance to 27 at 1200 rpm idle. No problems.
       
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      • Murray

        Murray FABO Gold Member FABO Gold Member

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        15*-18* with no vacuum advance.
         
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        • mbaird

          mbaird mbaird

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          I think the related issues are not so much kickback but carb tuning .
          A/J has written at length ( no pun intended) on this .
           
        • RustyRatRod

          RustyRatRod Lemmie see your b00bs. FABO Gold Member

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          It's all combination dependent, but yes, a lot of people run initial timing into the 20s. The more cylinder pressure one has, the less initial it will stand.
           
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          • A Body 440 WHY NOT

            A Body 440 WHY NOT Well-Known Member

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            General terms.
            let’s say 20 degree initial
            I am not sure about how much the vac Adv is right now
            Mechanical should be restricted so the initial + mechanical + vac = total around say 34 degrees ?

            Another question is the vacuum ( which I won’t have much of ) comes and goes due to load and throttle position. Needs to be fully in this equation ?
            Thanks :poke:
             
          • yellow rose

            yellow rose Overnight Sensation FABO Gold Member

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            Forget about vacuum advance until everything else is happy. I seriously don’t any big lock will be happy with 34 total unless it is a B1 head or better. 38 is more likely the least it should have and may go as high as 42 unless there are other issues.

            I don’t know about your converter (love that cam BTW) but you’ll need at least 20 initial (base) and that means it can NOT drop below 20 degrees when it goes into gear. That’s at a minimum.

            I don’t know what you have for an ignition system, but it needs to gain advance all the way to peak torque and at that point it should continue to add advance to max RPM.

            The total timing will be affected by how much retard the box has with RPM.

            Once you have that part sorted out, you can work with the vacuum advance. You will probably be able to add 10-15 degrees of advance with it but when it comes in will be critical.

            You may also be able to (MAYBE) use manifold vacuum instead of ported (timed) to pull the advance a bit quicker, like idle and above but you just have to test for that.
             
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            • AJ/FormS

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

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              As to kickback, it's all about EFFECTIVE cylinder pressure.
              What is a 10/1 engine?
              This is a ratio of cylinder volume comparing it between when the piston is at the bottom to when it is at the top. By itself it is not very meaningful.
              Why is that?
              Because compression cannot start until the intake valve is closed and not leaking. With a small cam, this starts early enough, that the Dynamic compression ratio can be fairly high. But the later the intake valve closes, the less the Dynamic ratio can be.
              What is Dynamic CR?
              It is the same as Scr except the swept volume does not begin until the intake valve is closed. Dynamic CR can vary wildly in the came engine, at the same Scr, with different cams, but rarely gets closer than 1.5 point less than the Scr.
              There is a third Compression Ratio for throttled engines namely Effective CR or ECR. When the throttles are closed, very few air molecules can actually find their way into the chambers. So even tho you have a 10/1 engine, that big cam of yours might bring the Dcr down to say 8.2 (just guessing) but worse is that your 10/1- 440, has a total volume of say 900+100=1000cc with the piston at the bottom, But, maybe only 300 cc worth of air, when measured outside the chamber, actually gets into there during cranking ,with the throttles closed, So your ECR might be 1000/300= 3.3 to 1.
              But say during cranking, you open the throttle some, and now 500cc of air gets in there. And so, now, 1000/500= 5/1 ECR.
              So now you can kindof see why 20* initial is not that big a deal.
              But it gets worse.
              When you start the fire, at some early number like 20*, there is way more than just 100cc of minimum chamber volume,above the piston; So your actual ECR at the time of ignition might be even lower than 5/1.
              But it gets even worse.
              When the engine is cold; of the fuel that gets into the plenum, most of it is gonna puddle on the cold intake floor. Some of it is gonna stick to the various cold port surfaces like rain sticks to your windshield at 60mph. And some of the drops, when they get into the cylinder are too big to burn and they are gonna go right out the tailpipe, unburned. So what do you do? You put a few pumpshots into the intake, in the hopes that there will be enough fuel in suspension, that maybe it will catch fire.
              But it gets even worse!
              With 1000 ccs of space in the total chamber volume,the finally inducted elements of gasoline and oxygen have to wander around in there and find each other, cuz if they don't find eachother, they cannot chemically react to produce heat, which is the author of the motive force that eventually moves your car.
              And that is why you start the fire so darn early in the low-efficiency mode of starting.

              A soon as the engine is warmed up, you don't need the early timing any more, but AFAIK, nobody has ever made a stand-alone self-switching system.
               
              Last edited: Nov 25, 2020
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              • A Body 440 WHY NOT

                A Body 440 WHY NOT Well-Known Member

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              • A Body 440 WHY NOT

                A Body 440 WHY NOT Well-Known Member

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                thanks for the info. !
                I have a MSD box that is black with mopar on it. Has a 6000 chip.( Basically a 6al box I believe )I have a stock electronic dist that I will be recurving. You say with RPM the box will pull timing out ? I didn’t know that.
                 
              • A Body 440 WHY NOT

                A Body 440 WHY NOT Well-Known Member

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                wow. Great info !!
                Thank you.
                 
              • yellow rose

                yellow rose Overnight Sensation FABO Gold Member

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                Yeah, it will retard with RPM. I could post a video of it happening on my machine, but I caught the poo poo the last time I posted it here, so I will go find the third party video I saw that made me buy my distributor machine.

                I figured if it was true that ALL ignition boxes retard with RPM (and it IS a fact that they do) then it’s near impossible to set an advance curve without a test bench.

                So I found my and bought it. And I have verified it happens.

                I’ll go find the video and post a link so you can see it happen.
                 
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                • yellow rose

                  yellow rose Overnight Sensation FABO Gold Member

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                  So I can only find the video made by William Baldwin on Face Book so I’m going to post my video.

                  It’s pretty self explanatory.

                   
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                  • A Body 440 WHY NOT

                    A Body 440 WHY NOT Well-Known Member

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                    interesting .
                     
                  • A Body 440 WHY NOT

                    A Body 440 WHY NOT Well-Known Member

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                    Ok. So hypothetically speaking.
                    20 degree initial
                    20 degrees mechanical which means 10 degrees at the dist
                    40 degrees total
                    Don’t worry about vac can right now. for a starting point ?
                     
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                    • A Body 440 WHY NOT

                      A Body 440 WHY NOT Well-Known Member

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                      Thanks :thumbsup: For your time and knowledge
                       
                    • RustyRatRod

                      RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                      No. vacuum is not considered when setting timing. It just ends up "where and what it is" unless you have an adjustable can. Total is initial plus mechanical. PERIOD. It's not uncommon and perfectly normal to have as much as 60 "or so" degrees incluging vacuum advance. The vacuum advance is only there to clean up combustion at part throttle and offer "a little" part throttle acceleration help. Since vacuum drops out on acceleration, it's not included when measuring timing.
                       
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                      • Lefty71

                        Lefty71 Well-Known Member

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                        Depending on your wiring of course..... Can you crank it, then hit the ignition?? If so, not a biggie anyway
                         
                      • Rmoore

                        Rmoore Well-Known Member

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                        You are a wealth of knowledge ! Much respect Sir
                         
                      • RustyRatRod

                        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                        40 is a bit much. Usually small blocks like around 36 total give or take, big blocks a tick less.
                         
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                        • Early a body

                          Early a body Well-Known Member

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                          I have done a lot of reserch on this topic. Even found a real good slant six club magazine that spells everything out written by doug durta.

                          Go to FBO Performance Ignition for all Makes, Muscle Cars, Street Rods, Race Engines. Specializing in Mopar Ignition Products, Distributors to Computer control ECU's.  Home of the HRR688,

                          I use his plates in the distributor plus he has great info on his website.
                          On all my cars with the decent cams I have set them anywhere between 16- 20 degrees at idle. use his plate to lock out the distibutor so I only get 35 total mechanical. And I use the vacumn advance

                          He even has bushings for MSD distributors, more than what you can get from MSD

                          I even did this on a slant six that was crazy hard to start and would idle like crap. This slant has 4 barrel and an agressive cam ( installed in 1991 cant rember the specs anymore) Once i upped the timing to I think either 10 or 12 degrees ( its been awhile) put the plate in it starts after a few cranks and never stalls anymore.
                           
                        • AJ/FormS

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

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                          Not just me, we're kindof a team around here. There's lots of guys here smarter than me and some to many regular contributors that have vastly more knowledge and or experience.
                          I only know two things in this world, maybe three, namely Bible, a street 360, and ....... um , ohchit I forgot #3. And I'm not really all that up to speed on any of them, but I muddle along pretty good.
                           
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                          • QuickDart360

                            QuickDart360 Well-Known Member

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                            I set my 360 to 16° initial timing. Distributor is from fbo with limiter plate. Cam is the 292/508 mopar cam. Seems to start fine. Also runs well. Question is can I try more initial or just keep driving? Really only left this way since it came @ that setting since purchase. This distributor was used before with 280 mopar cam too.
                             
                          • famous bob

                            famous bob mopar misfit

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                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                            hahaha , u said at length , what a mouth full !

                            I run 23 intitial on my 440/505 , with the vaqccum advance turned on in my fuel inj set up .------34 total
                             
                            Last edited: Nov 26, 2020
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