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Ignition Timing questions

Electrical and Ignition

  1. Ralph

    Ralph Well-Known Member

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    I have a 340 high performance crate engine.
    Engine builder states "use a mechanical timing curve of 14 degrees at 700 rpm, 27 @ 3000 and 29 degrees total at 4000 plus rpm".
    So teach me something - I set the initial timing at 14 degrees btc and then adjust mechanical type distributor for 15 degrees for a total of 29 degrees btc ? or 14 degrees plus 29 for a total of 43 degrees.
    I was going to look into a Mallory unilite which states can be adjusted from 14 to 28 degrees
    Nowhere near a stock cam .504 lift etc
    Any advice would be helpful.
    Thanks to all
     
  2. Adam

    Adam Well-Known Member

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    I am not very concerned with the base timing; usually around 5 to 10 btdc to get it running. I use an adjustable timing light to dial in 34 degrees at 2500 rpm. You can rev it up past 2500 and watch that you don’t get any more advance. This is with a Mopar vac adv. distributor, vacuum adv is reconnected after timing is set.

    Some guys like 35 degrees at 3000 rpm, which is fine. I find my distributors (modified by 4Secondsflat.com) mechanical advance is all in by 2500, use whatever works for you.
     
    Last edited: Oct 10, 2019 at 10:01 PM
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  3. Cudakiller70

    Cudakiller70 Well-Known Member

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  4. Cudakiller70

    Cudakiller70 Well-Known Member

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    FWIW my 340 with cam, headers and RPM intake. initial is set at 18 @ 800. My total mechanical advance is 34 @ 3000. No vacuum advance. I limit my total by using an FBO advance plate, see pic. Also using lighter spring (only 1 was changed) from mr gasket
    EC9A93A4-50F0-406F-A00D-6CE4763E5088.jpeg
    I use a stock electronic distributor.
    There are a bunch of ways to go for ignition. Do you need a complete ignition system? If you already have a system and just need a recurve of your distributor, there are places to get your distributor recurved. Again if a complete system is needed, I like FBO. Don also has a good tuning book and good plug reading info on his website. Many other ignition choices for these cars.
     
    Last edited: Oct 11, 2019 at 12:07 AM
  5. Ralph

    Ralph Well-Known Member

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    Thanks to all for the information.

    I will be reaching out to FBO on monday.
     
  6. moparleo

    moparleo Well-Known Member

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    There is a reason that the engine builder recommends that info on the timing curve for that build. Give that ifo to whoever you choose to plot your advance curve, but follow the builders advice . If it didn't matter why would he bother to tell you to do it at all ? Every bodies engine combo is different. That is what a "tune" is for. To Tune your combination.
     
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  7. crackedback

    crackedback Active Member

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    If the info is based on a dyno run, the "in car" may be different. BTDT. The total number sure seems low at 29 unless it's super efficient or has a bunch of compression and can't handle a higher total.

    Setting timing using total advance on a street car is a terrible method. I've mentioned the scenarios before using two different mechanical advance set ups in distributors. One runs like a beast, the other smells like a fuel truck dumping gas on the street. Fixed a bunch of the "total timing" set ups over the years.
     
  8. 12sandwich

    12sandwich Active Member

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    10ish initial 34-36 total all in around 2,000 rpm seems to work on a small block pretty well.
    For some reason the 440 I built would take all the initial timing and total timing you could throw at it. I still kept it somewhat conservative, as it’s a street car, though I have the vacuum advance not attached and use a mopar distributor with one stiff and one weak spring. Got a whopping 11.7 miles per gallon going to the mopar nats a couple years ago.
     
  9. Ralph

    Ralph Well-Known Member

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    crackedback, interesting comment on fuel.

    I am presently setup at 11 degrees initial with no vacuum advance with a stock mopar distributor which had some work done.
    I have a real smell of fuel a little with average driving but when you put the pedal dowm you get a good wiff of fuel.
    Does a fuel smell mean too much timing ?

    Thanks to all for the comments. Either way i am going to call FBO and start with the engine builders directions and maybe go a little more towards 32 or 34, see what FBO recommends.
     
  10. 12sandwich

    12sandwich Active Member

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    What’s the carb on the car?
    What temperature does it run?
     
  11. Ralph

    Ralph Well-Known Member

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    carb is edelbrock AVS 2 650 cfm

    temperature runs around 190 / 195
     
  12. moparleo

    moparleo Well-Known Member

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    Have you talked to the builder again yet ? Or just go to a good dyno shop in your area and spend some money to get it dialed it. No guessing.
     
  13. 12sandwich

    12sandwich Active Member

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    I’d run the timing up to where it sounds good, and drive it again.
    As long it doesn’t have any detonation it won’t hurt it, and you’ll eliminate the timing.
    If it’s still there, then you’ll know to look at carburetor or fuel pump or pressure, possibly weak spark?
    I run Holley on all my junk, so they always smell a little fuelie when first started, especially the six pack car, as the choke works.
    Goes away after warmed up.
     
  14. crackedback

    crackedback Active Member

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    504 cam lift. Not knowing duration, I'll guess it will want 18-22 initial timing. Don't drive it that way, see if the idle tune comes around. If it does, fix the mechanical advance in the distributor to hit the total numbers. The engine will likely be a bunch more snappy off idle with more initial timing.

    Simple test. Start the car, warm it up to operating temp. Twist the distributor a smidge counter clockwise, if the idle speed picked up, the engine wants that timing.

    I don't care what the builder says about timing at idle. On the dyno under no load and in a car, especially with an auto car, the idle dynamics can be very different. One other thing, if you pull the car in gear and the idle drops a lot, more than 100-150 rpm, it likely needs more idle timing.
     
  15. Ralph

    Ralph Well-Known Member

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    Got it, will check it out but not till next week.

    Is there a way to check for weak spark, fuel pressure regulator set at 5 psi and carb was changed with little improvement
     
  16. Ralph

    Ralph Well-Known Member

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    Cam specs
    valve lift .504
    duration at .050 - 224 224
    lobe lift .3360
    separation 112
    duration at .006 - 272 272
    degree intake lobe to 108

    340 automatic car, 650 edelbrock 650 AVS2 carb,fuel pressure set at 5 psi,355 rear, converter stall 2000, everything rebuilt, can bring it to dyno when setup correctly.
    other than gas smell car drives good.
    idle seems good and better power at 11 degrees btdc, tryed 14 and seem not so good so returned to 11 degrees.
     
  17. 12sandwich

    12sandwich Active Member

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    I’m not a fan of those carbs, so I’m a little weak in there operation.
    I’d tear the cover off of it, and check float level, make sure it’s clean especially around the metering rods.
    If it’s all good, consider an msd ignition, there strong in firing fuel at low speeds, especially at idle.
     
  18. Ralph

    Ralph Well-Known Member

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    Thanks to all
     
  19. 12sandwich

    12sandwich Active Member

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    Some of these guys have forgotten more then I know.
    Those carbs seemed to work well when properly adjusted. There was a learning curve though.
    Someone here can probably lend a hand on the fine tuning of an AVS Style carb.
    I’m a Holley guy, and if I owned a Hemi car with 2 of those junkie excuses for a carb, they’d be swapped in a weekend.
    I had a guys all original Hemi car recently for a week, or more actually, for some repairs. What a PIA to start this thing when cold.
    Actually so was the 67 GTX he had in a couple weeks before that, another all original car.
    Something about the idle characteristics of AFB or AVS, Thermoquad I don’t like. Granted there better when warmed up.
    It just reminds of how well my junk runs, and starts. I can count the cylinders firing on everything I’ve built, and they don’t die when cold, and can idle at stupid low rpms.
    Long live Holley, and Mopars
     
  20. i_taz

    i_taz Well-Known Member

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    If the fuel smell is more constant you might want to try lowering the floats. I set timing at 32 and had some results with a pressure reg but what resolved it for the most part was setting the floats 7/16 half way back on the floats not at the end on my Performer 750. I stumbled on a youtube video of a guy putting a 5.0 in a Mazda and he mentioned that if the bowls are too full they leak down past the jets. My plugs were so clean I was more worried about leaning it out too much trying to clean up the dirty exhaust...They had a about 1K on them and you could see the fuel distribution the intake had...#8 was as white as new