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Spark plug gap question

This is a discussion on Spark plug gap question within the General Help forums, part of the LSx Technical Help Section category; Just bought some ngk tr-55's and was wondering if anyone knows if they come pre gapped? If not does anyone ...

  1. #1
    Member ldurham's Avatar
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    Spark plug gap question

    Just bought some ngk tr-55's and was wondering if anyone knows if they come pre gapped? If not does anyone know the spec for them? Thanks!

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    Smiles for 9.5 Years cammed goat's Avatar
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    I believe they come pre-gapped at .040 or .045 which is what GM requests.

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    Member ldurham's Avatar
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    Ok cool
    Thanks!

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    I have mine set around .052".

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    Member ldurham's Avatar
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    They came pre gapped at .055".

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    You need to tighten that up to .040" before installing. The original spec was .050" which GM changed a looong time ago. Ask Sarge he's old enough to remember...hehe.
    Anyway, it is good practice to check them yourself before installing not just take it on faith that they are right.

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    Retired NOT tired SteveC's Avatar
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    I have mine gapped @.055, and have no problems whatsoever.

    SteveC

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    Member ldurham's Avatar
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    I checked them all before installing them, all at .055, how would you go about tightening that gap up if I wanted to?

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    Moderator Firebirdjones's Avatar
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    I prefer to tighten mine to .035

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    Senior Member Z28_Driver's Avatar
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    Press the electrode against a clean solid object. I use the edge of my vise. Check and adjust the the gap until you get it right. Give it a try and you'll do just fine.

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    Moderator Cutlass's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    I prefer to tighten mine to .035
    Why so tight?

    I put mine somewhere in the .050s range. I think it was .055"

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    Moderator Firebirdjones's Avatar
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    For several reasons.

    Good ole Smokey showed back in the 60's that increasing the plug gaps with hotter ignition systems didn't do anything for HP on the dyno. Some might say this doesn't exactly fit with today's technoligy. Yes and no.
    When we played with plug gaps on the dyno we never really found any advantages either. Basically, and the general consensus among other engine builders, was that there is really no need to make the ignition system work any harder than it has to by increasing the plug gaps.
    When power adders are added to the mix plug gaps tighten even more in an effort to stop blowing the flame out under high cylinder pressure conditions.

    Kenny Duttweiler found that the stock LS coils will support up to 1500 HP several years ago. But the important piece of info to make that work was the plug gaps that he used to make it work. He tightened them to .020 The system simply isn't strong enough to jump a larger gap under those conditions. That's an important piece of information that I see alot of builders (mistakenly??) leave out. Most builders will recommend tightening the gap even on naturally aspirated setups as the power level goes up. So you can start to see the reasoning behind it.

    I don't make that kind of power, and others may not agree with tight gaps like that, but like I've heard so many times before, there is no need to make the ignition work harder than it has to because there isn't any power found with the larger gaps. So that's why I've stuck with what I use.
    Plus over time, as your electrode wears down and the gap increases, I'm generally never beyond the spec that GM calls for

    So I tend to run a tighter gap on all of my stuff, especially on single coil setups, whether it's points, or with GM HEI's, and even aftermarket digital MSD setups with multi spark capacity.

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    Retired NOT tired SteveC's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    For several reasons.

    Good ole Smokey showed back in the 60's that increasing the plug gaps with hotter ignition systems didn't do anything for HP on the dyno. Some might say this doesn't exactly fit with today's technoligy. Yes and no.
    When we played with plug gaps on the dyno we never really found any advantages either. Basically, and the general consensus among other engine builders, was that there is really no need to make the ignition system work any harder than it has to by increasing the plug gaps.
    When power adders are added to the mix plug gaps tighten even more in an effort to stop blowing the flame out under high cylinder pressure conditions.

    Kenny Duttweiler found that the stock LS coils will support up to 1500 HP several years ago. But the important piece of info to make that work was the plug gaps that he used to make it work. He tightened them to .020 The system simply isn't strong enough to jump a larger gap under those conditions. That's an important piece of information that I see alot of builders (mistakenly??) leave out. Most builders will recommend tightening the gap even on naturally aspirated setups as the power level goes up. So you can start to see the reasoning behind it.

    I don't make that kind of power, and others may not agree with tight gaps like that, but like I've heard so many times before, there is no need to make the ignition work harder than it has to because there isn't any power found with the larger gaps. So that's why I've stuck with what I use.
    Plus over time, as your electrode wears down and the gap increases, I'm generally never beyond the spec that GM calls for

    So I tend to run a tighter gap on all of my stuff, especially on single coil setups, whether it's points, or with GM HEI's, and even aftermarket digital MSD setups with multi spark capacity.
    But certainly (Sir), a 48K volt coil discharging through a 10" wire will deliver ALL the spark needed no matter what the gap.

    SteveC

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    Good info FBJ! Not disagreeing with anything you said, but I did leave my gaps opened up at > .050" for the simple fact that it is a coil per cylinder ignition system. Back in the day, a single coil ran all 8 spark plugs with much shorter saturation time than our individual coils have. I will keep the info you posted in mind for my next plug change.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by SteveC View Post
    But certainly (Sir), a 48K volt coil discharging through a 10" wire will deliver ALL the spark needed no matter what the gap.

    SteveC
    That theory may work on stock or near stock engines, but it's not true when you really turn the wick up. As I stated Duttweiler had to tighten the gap to .020 even with this coil per cylinder setup. Not to mention the general consensus from the engine builders I was hanging around was that wider gaps just makes the coils work harder and not only was there no need for that, but there were no changes on the dyno. So in essance it was unnecessary to run a gap that large.
    The large gap stuff really took a strong hold when HEI's came out in 75. GM wanted to see .045 or .050 with those ignitions too. The idea was a more complete burn and better emissions. Well if you have a more complete burn you should also have more power as wasted fuel is wasted energy, which is lost power. When it couldn't be shown on a high tech dyno monitoring EGR's, AFR's, BSFC's, etc...and the HP didn't change, it sort of put a lid on that theory as far as I'm concerned. (like I said Smokey proved that back in the 60's) HP increases from high fire electronic ignitions didn't come from the larger plug gaps,,,it came from the more accurate ignition systems. That's not to say GM has their reasoning for larger gaps, I just don't follow it.

    Everyone can take that for what it's worth, I'm not here to sell it. It's what I've found to work just fine, and if it's less strain on the ignition system I'm all for it.
    Last edited by Firebirdjones; 09-05-2011 at 09:59 AM.

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    This is good info.

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    Moderator Firebirdjones's Avatar
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    I'm full of useless information, I just don't always share it

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    Quote Originally Posted by Firebirdjones View Post
    I'm full of useless information, I just don't always share it

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