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HEI Ignition, Plug Gap ?

Discussion in 'The Hokey Ass Message Board' started by Candy-Man, May 8, 2013.

  1. Candy-Man
    Joined: Mar 21, 2006
    Posts: 1,713

    Candy-Man
    Member

    Just wondering what the norm is for spark plug gaps on an HEI Ignition (0.060") ? Any difference for street compared to a race motor ?
     
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,530

    Mr48chev
    ALLIANCE MEMBER

    I think most sources are now suggesting .045 for most applications.
     
  3. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    Unless it's 14-1 or running boost .045 is a good compromise for spark duration and gap geometry.
     

  4. UnsettledParadox
    Joined: Apr 25, 2007
    Posts: 1,107

    UnsettledParadox
    Member

    in all of my HEI swaps i bump the spark plugs up to a .040-.045 gap and they love it
     
  5. Candy-Man
    Joined: Mar 21, 2006
    Posts: 1,713

    Candy-Man
    Member

    13.1 and on race fuel ?
     
  6. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    I don't see any advantage over .035. Wider gaps shorten the spark duration. The wider gap is more of a part throttle advantage.

    "I think it helps to think of the ignition as having available energy in wattage or volts X amps X real time in milliseconds. The spark duration in Milliseconds is apart of the equations and the less volts you need the more amps and duration of spark and vice versa. Voltage is needed to overcome the gap so if you have a larger gap it takes more voltage, however, there is less available amps & spark duration i.e. the compromise. "
     
  7. hobbyjp
    Joined: Mar 14, 2006
    Posts: 327

    hobbyjp
    Member
    from socal

    All the HEI is doing is replacing the points with an electronic unit that breaks the circuit and allows the coil to push its charge to the spark plug, HEI also eliminates some of the maintenance associated with using points. Why would changing the method of how the electric field is broken have any effect on spark gap?
     
  8. spinout
    Joined: Jan 15, 2008
    Posts: 333

    spinout
    Member
    from Dallas, TX

    A respected engine builder and dyno man told me the days of the wide gaps are over. He says just check the plugs, and install as purchased. Hmmmmm.
     
  9. 61 chevy
    Joined: Apr 11, 2007
    Posts: 891

    61 chevy
    Member

    ok, does a high output coil help in a engine HP ?? :confused:
     
  10. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    The gap adjustment can be crucial to proper engine operation. A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, but the plug will almost always fire on each cycle. A gap that is too wide might prevent a spark from firing at all or may misfire at high speeds, but will usually have a spark that is strong for a clean burn.

    I install them at the tightest end of the gap required, so as they wear, they will wear through the operating spectrum. If you go wide, it will wear outside of perameters immediatly
     
  11. Not true. HEI, or products like our PerTronix Ignitors will increase voltage to the spark plugs. How you ask? With an improvement of the current fall time which increases coil output. On top of that something like our Ignitor II which has the patented Adaptive Dwell can develop up to 4 times more available energy, especially in the most used RPM range of 3,000-5,000 RPM.
     
  12. hobbyjp
    Joined: Mar 14, 2006
    Posts: 327

    hobbyjp
    Member
    from socal

    Its kinda hard to put validity to your claim hotroddon when your post is just a placement for your product. HEI and points are only switches in a circuit that break the current. Dual points also have a adaptive dwell, you just have to manually set em. With that said Ive pulled more pertronix units out of bad running classics then I have points. Id like to see some kind of proof that a HEI system increases your coil output compared to a point system that is in good factory working order.
     
  13. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio


    I respectfully dis-agree. I don't have a dog in this hunt, but I know that coils are different between point and HEI.... I also know what a huge difference it makes on a cars performance, Probably because....

    Points based ignition puts out roughly 20,000 volts

    HEI puts out 50,000 volts

    In addition, the spark voltage increase in HEI versus Points, the points voltage is dependent on contact effectiveness, and poor sparking can lead to lower engine efficiency. A mechanical contact breaker system cannot control an average ignition current of more than about 3 A while still giving a reasonable service life, and this may limit the power of the spark and ultimate engine speed.
     
  14. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    Fixed it for you, gap * psi * composition of gases in gap = spark demanded (ignoring rotor gap/ wire capacitance).

    If you look at an idling HEI closed loop carbureted car the plug firing voltages will vary up and down as the mixture changes. Choke the carb and they will go low, if they don't respond to mixture changes you have external resistance.

    HEI's never require 40,000 volts to fire unless there is a major problem.

    Many ignition scopes overread the high end firing voltages because the clamp on pickup is non-linear.

    They also vary in accuracy by what type of wire they are clampled on.

    Dynoloading a 3.8 SFI regal would require about 20KV with .060 gap plugs at full boost.

    We used a High Speed Tetronix DSO with a 100KV lead to measure voltages at the plug. A popular "scope" would read anything over 25KV as 40 but was accurate at 15 KV.

    When we went from the .040 Gap Kettering in 74 to the HEI we went from average idle KV's of 10 to the .060 gap HEI in the 74 455 it could fire a .060 gap plug @ 12-14 KV with a 1.8ms burn time instead of the 1.3ms burn of the Point.

    Also, another thing we ran across is that reverse wired coils did not require more voltage to fire universally, at idle they were lower (see the positive cylinders on a wasted spark) but as load increased and the center electrode got hotter than the ground electrode then a reversed polarity coil would require more voltage. It was fighting the hot cathode (negatively polarized) tendency to emit electrons toward the positive polarity ground electrode.

    Yes normal plug firing voltages are negative.

    So HEI and systems like Pertronix Ignitors store more energy and can have faster current fall.

    But unless there is a problem the plug gap condition at the time of ignition determines the "required voltage" to make the arc, then the residual energy will maintain it until cylinder pressure starts to build, you can see this on a scope as the burn line starts up until it extinguishes.

    Hoop
     
  15. hobbyjp
    Joined: Mar 14, 2006
    Posts: 327

    hobbyjp
    Member
    from socal

    I gotta get back to the drill press but I think you guys are adding puffery to a switch. the coil gets its charge from the battery through the ignition switch. The HEI doesnt add a charge to the coil, it tells the coil when to release its charge then the "distributor" distributes that charge to the proper spark plug wire. It might be slightly more efficient or just new compared to an old worn out points set but its doesnt change the charge. The reason sometimes different coils are added is because a different resistance is needed for everything to work properly.
     
  16. hobbyjp
    Joined: Mar 14, 2006
    Posts: 327

    hobbyjp
    Member
    from socal

    hoop, could you explain what exactly the longer burn time achieved?
     
  17. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,864

    Truckedup
    Member

    It's been mentioned several times here by ignition service guys using testing equipment that 50K volts means nothing to most guys here. Carbureted engines with with typical slightly rich fuel mixtures need less than 10K volts to fire the plugs . You start really pushing 50,000 volts through spark plug wires and caps,they will not last very long.
     
  18. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    The HEI and other systems are more than switches. They don't use a resistor to control the Coil primary current they sense current and then limit it at a peak value.

    [​IMG]

    Smarter systems over the years do smarter things with primary current control.

    The higher current and coil inductance give you a faster charging coil with more stored energy at discharge.

    In the 60s we had transistorized ignitions that worked as you describe.
     
  19. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    Better ignition cyclic repeat-ability. The ignition would sometimes flameout and if the burn was still continuing it would relight. So it tended to improve MPG, reduce HC. This was true up to the point of the extra energy required needing more fuel than was saved.

    In general it extended the lean misfire limit and would work with less homogeneous mixtures, larger fuel droplets etc.

    Multi- spark ignitions perform a similar task in a different way.
     
  20. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,864

    Truckedup
    Member

    A few years ago I experimented a lot with ignition on a modified 302 GMC in my 37 Chevy truck.The negine has 9.25 compression hotter cam headers etc.I am a hobbyist not a pro tuner. Messing around with lean part throttle fuel mixtures, aggressive spark advance and heated intake manifold. Yes,the engine was on the edge of detonation.
    Leaned out the carburetor until the engine hesitated at part throttle with a points ignition.Then I installed a Mallory 6A multi spark box using the same 15 buck made in Mexico coil.The hesitation was gone and I leaned out another jet size.
    Then I put in a recurved GM separate coil HEI and disconnected the multi spark box.The HEI was close to the multi spark box in performance at part throttle.
    I can't say the Mallory box or HEI was better at full throttle than carefully adjusted recurved stock points distributor,but obviously points need attention to remain in tune.
    This was my experience, yours may be different.
     
  21. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    We would find the lean misfire limit of cars and then see how far out we could push it. Our results were consistent with yours. Some engines were very sensitive to plug geometry, even plug indexing. We fixed a buy back 2.2 Chrysler by grinding back the ground electrode and side gapping it tighter to get idle burn up to 2.2 ms.

    A longer burn time that decreases idle misfire could get you a few more degrees of exhaust duration and pick up 5 or 6 HP an a 2.3 Ford.

    Too many variables here but some engines are more gap sensitive and some are more burn sensitive.

    Race engines are really a simpler set of problems.

    The HAMB application I guess is that a modernized ignition system can make some of the old marginal fuel systems much better performers.

    We had a full EPA test lane setup, but at night there were lots of SCCA showroom stockers and drag cars on the rollers.

    Hoop
     
  22. GMC BUBBA
    Joined: Jun 15, 2006
    Posts: 3,384

    GMC BUBBA
    Member

    Good thread guys, like usual it is a mix of correct, maybe somewhat correct and just plain on incorrect. I am on my iPad and will write some more tomorrow when I have a actual keyboard.:)

    For now let's start with the original plug gap question.
    The answer is: plug gap goes with engine overall design , ie .compression, cylinder head design and air fuel mix. Installing the hei won't neccesarly need a change in plug gap if the engine hasn't experienced a change.
    Same with a coil, a engine idling at 5000 volts per cylinder and changing the coil to a high output will still idle at 5000 volts...
     
  23. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    But if we change it to a high energy system the Firing voltage will stay the same but the spark duration will go up considerably. This increase in energy may let us play with a more open gap to improve the odds of an ignitable mixture being there, or have the extra duration to give us a second chance if the first kernel extinguishes! Of course if it requires neither, then not much will happen.
     
  24. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    I was always concerned about the coils time to re-energize between firing.
    Along with the HEI pickups reliability, versus the points contact and wear....
     
  25. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    That's one reason we have coil on plug. Theoretically the pickup coil should have been more reliable but the wires would break where they entered the pole piece from the vacuum advance movement. So they start the die under advance.

    They also wound different pickups in different polarities,

    [​IMG]

    This caused all kind of issues because the negative going slope was now positive going and they switched in the wrong place.
     
  26. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,864

    Truckedup
    Member

    Many see an noticeable improvement from an electronic distributor or electronic points conversion because the points distributor is simply worn and the point gap varies a lot.
     
  27. Electricity takes the path of least resistance. If you open your plug gap to 0.060" it will take more power [electrical current] to bridge that gap. The current will be looking for easier paths and will find it with carbon tracks in the distributor cap and through insulation in old plug wires....distributor rotors also suffered with the 0.060" gaps....I always close the gap down to 35-40 thou and the parts last longer.
     
  28. for a lean mileage car i like .060 to .080
    takes the same voltage to fire that or stock as long as plugs in decent condition
    w0 overdrive i usually pull 18 MPG

    doing a car with 3.42 and OD and 350 w 500 CFM edel. gonna be interesting to see what it will do
    just got another 2 gas analyzer been without for about 18 years on that
     
  29. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    hoop98
    Member
    from Texas

    There is no doubt the wider the gap the higher the stress, assuming the plug gap is the point of highest resistance, of course there was also a benefit to the wider gap or they wouldn't have spent the money to make system last with the wide gap. A real problem happens when people take a car like a 90s GM 350 and never change the plugs. Then about 100K the voltage does find another ground path.
    The 231 in a Regal was kind of hard to get the number 6 wire all the way snapped on.

    If a car came in running on 5 you knew it was 6. If they kept driving it the next thing to go was the rotor so they ran on 0 or walk home mode.

    When people didn't maintain their ignition or we had plug wires partially off they were killing rotors, so we got new rotors.

    Then it burned thru to the coil screws.

    So if a HEI had circuit gap or wide gaps like .100 it would find a new path. Just spin a hei distributor with no plug wires but hooked up to 12 volts. But be careful where you hold it.

    I spent time at REMY with a Northstar plug engineer, yes she only did Northstar plugs.

    They go through an unbelievable number of compromises to pick that gap.

    Chances are most damaged tracked secondary issues didn't come from the 060 gap but from other sources of high resistance.
     

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