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Spark plugs smaller than origional ones

Discussion in 'VT - VX Holden Commodore (1997 - 2002)' started by Connor john, Sep 26, 2018.

  1. EYY

    EYY Well-Known Member

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    Old man worked as a mechanic for over 25 years specialising in rebuilding/building performance rotary engines. They only used NGK plugs due to recurring problems with other brands such as the ones mentioned above. Rotaries and 2 strokes are notoriously hard on ignition systems. On a standard 4 stroke reciprocal engine, spark plugs are hardly stressed so most, if not all brands will suffice but service life will differ.

    I also deal with NGK/NTK/KYB through work and they're awesome to deal with. They produce a great product and they'll go out of their way to help you, plus the plugs are also made in Japan, not china like some other brands...
     
  2. immortality

    immortality No more smoky bacon :( Staff Member

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    The Autolite plugs tend to wear out faster, at $20 for a set I'm not fussed changing them out a little more often.

    Put it this way, I'm running a L67 which have the BPR6EF-13 plugs as standard. I'm running almost double the boost of the standard motor and the last set of plugs I put in I gapped at 1.4mm and have done almost 20,000km with no hint of misfire. When I change them I'll measure how much they have worn (I expect to see about 1.45 -1.5mm gap but if they are less I'll put them back in). The only other ignition mod I have are MSD coils and Bosch LPG type leads. Apparently how I run this engine isn't supposed to be possible...

    I've been running the autolite plugs for about a year, before that I had NGK irridium plugs in the L67 as that is what it came with. Previous to that I have predominately run NGK plugs. I did try some Champion plugs and the engine ran fairly much the same as the NGK plugs. Fancy plugs I stay away from unless they are specified by the manufacturer. I just did Platinum plugs in a Subaru $220 later (and I got em at trade)....
     
  3. RWD4ever

    RWD4ever Member

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    I don't think anybody stocks the LPG spark plugs anymore, they would be special order. I have used the plugs for 5 litre V8 - they are only 1 mm gap.
    That's if you use LPG 95% of the time. If you run on petrol a lot, the L67 spark plugs (with 1.3 mm gap) might be better.
     
  4. Juice3

    Juice3 Active Member

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    NGK bpr6efs-15 are the best to use in my opinion
     
  5. mechanic

    mechanic Active Member

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    Spark plugs are the most over-serviced component on a car.

    Their operation is akin to a light bulb... they work 100% or they tend not to work at all. There's no taper-off in performance over 99.9% of their life. New plugs will do nothing for power or efficiency if the old ones still operate normally.

    Save your money and put this one back in. It looks to be in excellent condition.
     
  6. EYY

    EYY Well-Known Member

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    I think you have a little more research to do...

    As plugs age, resistance becomes greater and puts more strain on other ignition components such as coils, DFI/module and leads leading to premature failure of these components. Plugs often don't just stop working altogether, and it's not uncommon for worn plugs to give an intermittent misfire.

    When the ignition system is in good condition fuel economy, smooth running and power is definitely favourable.
     
  7. mechanic

    mechanic Active Member

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    Yeah, no.

    The resistance of a spark plug core is negligible compared to the air gap across the tip. In fact a high resistance is necessary for the ignition system to create the voltage it needs to jump the gap - hence additional high resistance designed into the plug leads. Some plugs have resistance built into them.

    A spark plug will start to misfire once it has reached the end of its life - I think we are agreeing here. The failure mode of a spark plug is misfire, which indicates end of life. Replace it at that point.

    Not necessary until that point, however.
     
  8. EYY

    EYY Well-Known Member

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    High resistance leads to excessive heat and burnt out components.

    Many plugs are a resistor type to prevent interference with electronic equipment, but this resistance is negligible.

    Trying to make claims without the info, knowledge or references to back it up doesn't help anybody.
     
  9. mechanic

    mechanic Active Member

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    Can you explain that in more detail with regards to ignition system operation?
     
  10. EYY

    EYY Well-Known Member

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    Simple. If the resistance (either internally, at the terminal, or between the electrode and ground) is much higher than specified, the current will follow the path of least resistance to earth/ground. When this path of least resistance isn't between the electrode and ground, the electrical energy has to go somewhere else.
     
  11. mechanic

    mechanic Active Member

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    OK, and how does this relate to the resistance of a spark plug?
     
  12. immortality

    immortality No more smoky bacon :( Staff Member

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    Spark plugs do wear out and may not be visible to the naked eye without some measuring tools. As the plug gap increases so does the resistance. The wasted spark ignition system on the Holden V6's does create some unusual wear in that the plugs on one bank tend to wear out the electrode and the other bank the earth strap due to the way the coils are wired. As the plug wears and the resistance increases it puts more load on the coils etc.

    Also, although plugs may seem fine and the engine may appear to run fine it may not be the case as the driver may not notice the slight occasional misfire, not until it gets bad anyway. Ideally you should be replacing plugs before this occurs. Plugs can also run fine under some conditions and yet misfire under others (lean cruise is a good one) that unless you know what you are looking at is often misdiagnosed.

    Anyway, plugs are cheap, if you spend an hour taking plugs out to just inspect (that would be some $50/hr+ on the workshop rate) you may as well put new plugs in unless of course they are ripping you off on the price of plugs too. Considering a set of plugs costs me $20-$25 it's not really going to break the bank.
     
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  13. mechanic

    mechanic Active Member

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    With respect, this is just not true.
    It’s like saying your fuel tank wears out faster when you overfill it.

    It doesn’t work that way. A coil is just a generator and storage device. You can’t force it to work harder than it’s capable of working, just like your fuel tank. It just reaches a working limit.
     
  14. EYY

    EYY Well-Known Member

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    Maybe you should change your name to ‘clueless’...
     
  15. mechanic

    mechanic Active Member

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    Thanks for the intelligent response EYY.

    Rather than shout insults from the land of anonymous, why don’t you bring a well thought out argument to the forum?
     
  16. Sabbath'

    Sabbath' Redblock Jesus

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    Way to totally contradict yourself and use a rubbish analogy while you're at it.

    Unlike a lightbulb, which is either able to produce light, or not depending on it being serviceable or not while a spark plug has a performance dropoff while still being able to perform it's function. Which is to ignite the air/fuel mixture.

    To only replace your spark plugs once a misfire occurs means you have pushed well past the products optimum life.
     
  17. the_boozer

    the_boozer no more VK

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    Not being an educated man I agree with immortality As the plug wears and the resistance increases it puts more load on the coils etc. The vehicles that don't get serviced are the cars that seam to blow coils maybe its just that fact that tight arses replace just 1 coil and don't change the plugs they cheap out and come back 3 months later needing another coil or some other gremlin is happening (low fuel pressure from not changing the fuel filter ever).
    Most well maintained vehicles do 250k on the original coils without giving any trouble (or do I just not see many holdens anymore?)
     
  18. immortality

    immortality No more smoky bacon :( Staff Member

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    P=IV and V=IR two of the most basic rules of electrical theory. Voltage and current change with resistance.
     
  19. mechanic

    mechanic Active Member

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    I agree, they do.
    How does that relate to this thread?

    I’ll go back to my original statement
    - Spark plugs don’t degrade in performance until the end of their life, and should only be replaced when they fail.
    - A failed spark plug typically misfires (maybe carbon tracked, cracked insulation etc) at the end of its life.
    - Spark plug misfire is symptomatic of end of life - replace it.
    - Failed spark plugs don’t increase load or wear on an ignition coil.

    Ignition coil current consumption will change with RPM or changes in dwell angle ONLY. Scope a coil primary and test it yourself.
    The coil is a step-up transformer and operates at or below its design parameters its whole life (unless internal short circuit etc) . Wire-turn ratio determines max current flow and max output voltage.

    High resistance outside of the coil WILL change the relationship between the peak voltage and burn time of the secondary side, but this has no effect on coil operation or life.

    I’m not perfect and open to being corrected, but PLEASE provide a sensible argument and explain why.
     
  20. immortality

    immortality No more smoky bacon :( Staff Member

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    Clearly I know nothing, plugs don't wear out, coils/leads don't fail etc and obviously I've been changing plugs/leads for no reason for the last 20 years. Damn, I could be rich if it wasn't for all those bloody plugs....
     
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