340 Initial timing questions

Electrical and Ignition

  1. midnight340

    midnight340 FABO Gold Member FABO Gold Member

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    I have been running 22*/34* or a bit more on my X head 340, ...both before and after a recent refresh and addition of the Lunati Voodoo 740 solid lifter cam (w/ EDM's.) Cam is 235/243 at .050 and lift of .526/.546.

    I have a 6A MSD box into a new-ish "Ready-to-Run" MSD distributor. I have 12* mechanical advance in the distributor. Motor compression 9:1. With the old cam I had done 1/4 runs ad various timing #'s and my mph was a bit higher at 34 than at any higher setting.

    I have read advice that says to set initial timing to max the motor will take. As in, with motor fully warmed up, keep adding idle timing 2* at a time till the motor wants to pull the starter down or back fires through the carb.

    Here's my question: Motor was fully hot, carb dialed in pretty well with A/F meter and reading of plugs, etc. I have have recently had idle set at 900 to 1000. I started adding timing 2* at a time then trying a hot start. I got all the way to 42* initial (where I quit) and still no resistance to starting just fine. WHY IS THIS?

    When the 340 is idling (both with old mild cam and with new Voodoo) I can start twisting the distributor to add timing and it will keep speeding up a little bit until I reach 40* and then will level off and not slow down till I reach nearly 60*.

    What is all this telling me????
     
  2. Wyrmrider

    Wyrmrider FABO Gold Member FABO Gold Member

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    your low compression for that cam methinks
    and no load
    do not do that max advance trick then get on it
    go back to the old plan and don't run any more than you have to- since you know how to curve the distributor
    vac adv?
     
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    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

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      Thanks for the response!
      Yes, I’m staying with the same timing. Was just exploring /experimenting. Lunati told me to run this cam and don’t worry that I don’t have 10:1.

      By the way I am loving this cam!! Very happy with the choice!!!
       
    • mopowers

      mopowers Well-Known Member

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      It likes a lot of initial advance. Assuming your TDC mark is correct. Have you double checked it? Whats the compression?
       
    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

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      Yes, double/triple checked TDC when degreeing the cam (with piston stop) and compression is a bit over 9:1. I both measured and cc’d the bore/valve reliefs and cc’d heads, etc. ...so that’s a definite.

      I was just curious why I could keep adding initial and it would still start OK warmed up on a 90* day.

      I’m sure I’m fine at 22/34 timing. Seems happy enough with that.
      (Vacuum can adds another 16 degrees.)
       
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      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Because there is no load on it.
        You can run it super advanced and super lean with no load. Way beyond what will be efficient.

        Should not need vacuum at idle using 22* initial.
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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      • mopowers

        mopowers Well-Known Member

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        I'm curious what your cranking compression numbers are. Have you ran any tests?
         
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        • RustyRatRod

          RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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          It's not about compression. It's about cylinder pressure. If an engine doesn't generate a lot of cylinder pressure, it's going to want more timing than one that does. Did you degree the cam in? I "just bet" that cam would run better and require less initial timing if you installed it a little more advanced than what Lunati recommends. Have you run a compression test? I bet a dollar it's under 150. While Lunati might say to "not worry" about what your compression is with that camshaft, it will perform better "with the right amount" of cylinder pressure.......which is not the same as, but is affected by static compression ratio. 9:1 static compression is "a bit low" for that camshaft. That in and of itself is the reason you're pulling in so much timing. That's not necessarily a bad thing. If it runs well and you're happy with it, run it. Just know that it could be "more efficient". ......but then........whose build couldn't? If you worry yourself chasing every little bit, you'll never have any fun.
           
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          • midnight340

            midnight340 FABO Gold Member FABO Gold Member

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            Rusty, you are correct. I could easily over-think it all. :D Much more fun to just drive!!! I’m not really too worried as it does run great, sounds very happy!

            I’ve only run a COLD compression test so far, will do it warmed up soon. Getting 150 cranking or just under, but very even. Happy about that as I didn’t touch the cylinders/pistons/rings. Just cam, valve springs, all new bearings, lapped valves and had the factory iron adjustable rockers bushed plus new shafts.

            264/272 235/243@.050 w/ .526/.546 lift. Huge improvement over the old .458 lift cam!!!!
            Intake center line installed at 107* Intake closes at 60* ABDC.
             
          • RustyRatRod

            RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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            Then if you're happy, I say to heck with all the experts, forum heroes and online calculators. That's all that matters. I kinda have always like overcammed low compression engines. They CAN run well, but moreover, they are usually very reliable and always sound great.
             
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            • midnight340

              midnight340 FABO Gold Member FABO Gold Member

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              Now that’s good advice!! Appreciated. I do love the sound. It has a crisper, sharper edge to it compared to the old longer advertised duration/lower lift cam. And I am actually enjoying the sound of those solid lifters too. Just seems more “real”!
               
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              • mopowers

                mopowers Well-Known Member

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                I say give it as much initial as it wants, limit the centrifugal advance in the distributor, and run the piss out of it.

                I had a similar question about my little 340 a couple years ago:
                Why so much inital timing???

                Mine is 9.6 SCR w/ 231* 108LSA + 4 HFT cam. Cranks at 165psi in all 8 and likes a ton of initial. I've got it set now at 28 w/ a total of 34. My take away message is that each engine has it's own little personality. Find what it likes and stick with it. Don't be afraid to run 30* initial.
                 
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                • RustyRatRod

                  RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                  Yes, limiting the total is very important. LAst thing you want is ti burn a hole in a piston at 5500 RPM with 50* timing.
                   
                • gzig5

                  gzig5 Well-Known Member

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                  So with the vacuum advance connected, you'd be at about 50 degrees at cruise? Is that how it's running now?

                  My 70 340 has a stock cam. I'm going to be fitting the FBO limiter plate to optimize the timing and I'm trying to decide whether to run the vacuum advance. 50 degrees sounds like a lot but I guess if the engine isn't loaded it's OK?
                   
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                  • midnight340

                    midnight340 FABO Gold Member FABO Gold Member

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                    Mopowers, thanks for that link.

                    I have read that 50 total is not too much for a lower compression motor as it's not working too hard at a steady run down the highway.
                    And I'll have to double check the vac. adv. #. I said 16, but I think MSD book says a max of 10 is available. It's been a while since I set up the distributor.
                     
                    Last edited: Jul 2, 2019
                  • RustyRatRod

                    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                    Right, and here's why! You never ever include vacuum advance when talking about timing. Ever. You always just let it "end up" wherever it is. There are adjustable vacuum advance cans, but that's not for the purpose of total timing. Total timing is initial, plus mechanical. PERIOD. It appears that you get that.

                    The reason the vacuum advance can "doesn't matter" is because it will never be in the picture while accelerating under a load. When the throttle is opened, vacuum drops off so the vacuum advance does not work then. It's sole purpose is to clean up the combustion at cruise and part throttle. That's "about it".

                    In fact......it says right in the Mopar Performance engine book that it's not uncommon to see 60* timing with the vacuum can attached at part throttle cruise. Perfectly normal.

                    Sounds to me like you got yours just about right. I don't think I'd mess with a thing.
                     
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                    • MOPAROFFICIAL

                      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                      Yep. The cranking/dynamic compression is too low.
                      Just set it up 18 / 34 and drive it is my opinion on it.

                      To the OP...
                      I'm sure its a blast and runs great anyways.
                      I say next time get one of those dumb calculators out, as RRR calls'em..lol...dont forget to wear "forum hero" cape....lmao couldnt resist.... and plot out your static comp or cam timing a little better so you can get all out of what you spent that money on.
                      Cheers.
                       
                      Last edited: Jul 2, 2019
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                      • Wyrmrider

                        Wyrmrider FABO Gold Member FABO Gold Member

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                        dont be afraid to run 30 initial?
                        Don't run any more at idle than you have to
                        be prepared for that batch of bad gas fill up out on the road/ hot weather. etc
                        as to the 34 suggestion TOTAL w/o Vac
                        works for most X-J 360 stock heads
                        later take less
                        once you quit improving back it down a notch and drive it
                        more advance past max power just makes additional heat and removes your margin of safety
                        lots of good ideas in this thread
                        glad that big cam works for you
                        not the way I'd do it but lots like that kind of build
                        your combo must work together well
                         
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                        • mopowers

                          mopowers Well-Known Member

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                          Not all engines tune by the book. My 340 picks up RPM as I twist more timing into it up to about 34* and doesn't kick back the starter during hot starts in 100* heat w/ shitty pump gas, even at 34*. It loves having 28* initial. Do I have to run 28* initial? Hell no, but it sure does start at a flick of the key, and responds very quickly off idle. I say run as much initial as the engine wants and that you can safely get away with.

                          If the OP's engine wants the initial timing (ie. picks up RPM as he twists more in), and doesn't kick back on the starter on a hot start, give the engine what it wants, regardless of what the timing light says. He's just gotta remember to limit the total advance to something reasonable that won't result in detonation under load in hot weather with shit fuel.
                           
                        • midnight340

                          midnight340 FABO Gold Member FABO Gold Member

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                          Bit of an overview:
                          Before picking the cam I did talk with, and get reccommendations from, Mike Jones, Dwayne Porter, Mike at B3, Howards, and with Steve Slavik at Lunati. (Initial design on the Voodoo cams was done by Ultradyne Harold and I liked that idea of using his lobes.) And I am getting enough vacuum to run my power brakes just fine.

                          Because my heads had a bunch of porting done to them i did pick a higher lift cam than some guys offered as I'd never felt I was using their potential. Went with solid as they tend work better if you don't mind setting lash. But I did compare all the exh. closing angles, overlap #s, etc. I just know it's a big improvement!

                          Yes I stayed with the old forged TRW's because my compression was even before, the bores/moly rings were in great shape. My open chamber iron X heads cc'd at 63, so they had been worked on there as well. To check exhaust valve to piston clearance I did clay, but then did put in hardware store springs and a dial indicator on it later. Exhaust to piston is 0.105" Close enough!

                          I am running one of the new Edelbrock 650 AVS2 with the annular boosters, LD340, and headers into 2-1/2" with Magnaflows. Cam is rated 2400-6600 but pulls nicely from just over 2000. Pretty wide torque and power curve.

                          I'll play with timing a bit more, maybe, but 22-34 works. I have an A/F meter on it so getting the mix dialed in is pretty easy, but am watching the plugs to see if they agree.
                          All in all, pretty pleased.

                          I love the threads on this site as there is so much knowledge (and a wealth of opinions!) that helps get things sorted.
                           
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                          • AJ/FormS

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

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                            So my question is; why are you running to 900/1000 idle rpm?

                            I have a 230/237/110 FTH cam with about the same lift, but with much more advertised duration (276/286/110@.008), and mine will idle down to 550rpm pulling itself along at 4 mph with 3.55s and a 3.09 low gear in the A833, with an ancient Holley 750DP. The neutral idle speed is whatever I set the timing to but no higher than 750 (12/14).
                            The secret is to set the transfer slot exposure to a little taller than wide, then leaving the idle speed screw alone. To set the idle speed you then use idle-air-bypass and timing. My idle timing is 12 to 14. To idle down to 550 I retard the timing to 5*(with a dash-mounted, dial-back, Jacobs timing-delay box). But the T-slot exposure remains the same, and the accelerator pump adjustments remain the same, so I get no tip in sag or bog/hesitation.
                            If you do it your way with 22 or more initial timing, then,to get the idle speed down to 700 or so, you will nearly shut off the transfers and have to open the mixture screws to full rich, so it will still idle. Then when you give it throttle, the transfers will be very lazy to get started and she may hesitate and even stall. To compensate you will increase the pumpshot, and it still won't be happy until the idle speed is increased, bringing the transfers back on line. In the end it is driveable, idles way too high, and sucks gas pretty bad.
                            Do yourself a favor, set the transfer slot exposure and start over; who cares what the idle timing is! If you have an automatic that cam wants a 2800rpm or more stall, so you should not care even a tiny bit what the timing is below the stall speed. Then, as soon as the car gets moving, the Rs are rocketing and you still hardly care what the timing is because she will almost instantly be at max WOT timing.And it will never be below max timing again at WOT, unless the Rs fall to below your "all-in-by" during a shift, in which case you shifted too early,lol.
                            The only time you care about timing between ~3600 and the stall, is when you are cruising in that zone, in second gear....... But that is where the Vcan makes up the difference, so modify yours to get about 22/24 degrees,( instead of the miserable 9* they often come with) and then you're in business.

                            Now if you have a manual trans, that's a whole nuther story
                             
                            Last edited: Jul 2, 2019
                          • midnight340

                            midnight340 FABO Gold Member FABO Gold Member

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                            AJ, I can tell you have a sweetly dialed in combo, and sense that you have a lot of fun driving. Always enjoy your imput.

                            I had been setting idle to about 750-800, but due to "something I read", about somebody feeling their cam oiled better at 1000.... anyway, I was just experimenting with setting it higher. Moved it back down some this afternoon.

                            This whole T-slot thing, I assume to be related to Holley style carbs? I am running an Edelbrock 650AVS2. Still tweaking rods after getting the jetting real close. A/F meter helps me keep an eye on things. I certainly do not have any hesitation off idle, or at any rpm when I mash the pedal. I have no hesitation whatever at any speed. It's right there when I want it.

                            Yes, I'm running an automatic (518) and 4.10 gears but with O.D. and 11" lock-up converter with a stall of 2500. This cam actually pulls pretty good from 2000 up, so works fine with the 2500 stall (which is what Lunati recommends anyway.)
                            PTC did the converter for me, and I had them do a freshen up when I had it out. I can cruise comfortably at 85mph or whatever semi legal speed on the interstate, and still run the 4.10's for fun in town.
                             
                          • 512Stroker

                            512Stroker We are all here because we are not all there.

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                            Do have the P/N or a link to your Voodoo cam I cant seem to find it
                            Thanks in advance
                             
                          • AJ/FormS

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

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                            I'm busted,lol.
                            But just to maybe ease your mind; my cam is an old Hughes HE3038AL flat/hydro. Specs are 276/286/110 and lifts of .549/.571 (1.6arms) and using their 1129 springs shimmed up some; enough to hit over 7200 without losing control.
                            The thing is, this engine has accumulated over 100,000 miles. The idle has never been set higher than 750, usually 700 (stick-car), and it has spent probably dozens and dozens of hours at 700 down to 550 rpm, cuz you know how those cams sound idling around at the car shows with retarded timing,lol.
                            However, I made a couple of mods, cuz, like you I was worried about the lobes. I increased my oiling to the topend for spring cooling, and cut some drain-back channels in my Eddies, and I drilled holes beside every lifter bore to let those factory junk-collecting low-spots dribble oil into the cam tunnel. Additionally I run a high-volume pump with a Milodon 7qt roadrace pan, and it's pick-up. And lastly, I always add one small bottle of ZDDP at every oilchange running any old dyno oil. I'm not kidding; whatever is on sale.
                            So with over 100K miles on her, Ima guessing it's working.

                            I don't run vacuum-secondary carbs anymore. Or carbs with air-valves. I'm not dissing them, I just like my 750DP; my car does what I ask it too, when I ask it too, and it's totally controlled and modulateable with the pedal.
                            Oh, she's a 3.09low Commando box with a GVod, that I use as a splitter. She runs 3.55s and 65=2240rpm (this is 110kph our Manitoba highest speed-limit, only found on the TransCanada hiway).
                            The fun gear is second gear where 32mph is 2700; well it is when the tires aren't spinning.That's one of the advantages of VP around 155

                            I'm glad you got the off-idle tip-in sag cured; that can be really annoying.
                             
                            Last edited: Jul 3, 2019
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