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spark plug gap

This is a discussion on spark plug gap within the General Help forums, part of the LSx Technical Help Section category; I just bought a new set of ac delco rapid fires what would you suggest gaping these at ? They ...

  1. #1
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    spark plug gap

    I just bought a new set of ac delco rapid fires what would you suggest gaping these at ? They are pregaped at .080!! what should they be?

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    they are actually pregaped at .060 which still seems to large to me.

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    Single Malt rbob93's Avatar
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    .060 is stock gap

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    Bone it like you own it FORD RECOVERY EXPERT's Avatar
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    Stock Gap IS .060"




    As you remove the old plugs gap the new ones, the general rule here is to remove .004 from the gap for every 50 HP you add to the motor. Then make sure you put the antiseize on the threads of the plugs. start about 1 thread from the end to be safe. Do not get any on the electrode parts or anything that comes in contact with the combustion chamber (pre ignition will occur)

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    The Bandit Wesman's Avatar
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    Quote Originally Posted by bryceslu View Post
    I would go .040-.045

    I gapped mine at .035 on basically stock LT1 when i changed them before.
    Why would you do that?? Makes no sense at all.

    You want to run the largest gap possible while still having enough voltage to bridge the gap and not cause a miss. A larger gap means more spark exposure to the combustion chamber, which improves power and efficiency.

    Older engines had to run small gaps because their primitive ignition systems didn't have enough power to bridge the electrodes. LS engines have one coil per cylinder with around 40,000V, so bridging a .060 gap isn't an issue. My spark plugs had eroded to around .080 by the time I started getting low RPM misfires, at which point I changed the plugs.

    The only reason you sould have to decrease gap is if you're running high compression or boost and you're getting spark blowout.

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    Member bryceslu's Avatar
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    OK OK theyre gone. My experience was with LT1's and i stated that but should have kept my mouth shut.

  7. #7
    Quote Originally Posted by Wesman View Post
    Why would you do that?? Makes no sense at all.

    You want to run the largest gap possible while still having enough voltage to bridge the gap and not cause a miss. A larger gap means more spark exposure to the combustion chamber, which improves power and efficiency.

    Older engines had to run small gaps because their primitive ignition systems didn't have enough power to bridge the electrodes. LS engines have one coil per cylinder with around 40,000V, so bridging a .060 gap isn't an issue. My spark plugs had eroded to around .080 by the time I started getting low RPM misfires, at which point I changed the plugs.

    The only reason you sould have to decrease gap is if you're running high compression or boost and you're getting spark blowout.
    GM disagrees with you. They have updated the gap for our engines to .040"

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    The Bandit Wesman's Avatar
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    Quote Originally Posted by Marc 85Z28 View Post
    GM disagrees with you. They have updated the gap for our engines to .040"
    Thats how it works, regardless of whether GM revised the spec or not.

    Probably too many people running their cars too long without changing plugs, and they were getting gap erosion and misfires.

  9. #9
    Single Malt rbob93's Avatar
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    Quote Originally Posted by Marc 85Z28 View Post
    GM disagrees with you. They have updated the gap for our engines to .040"
    Only if using the new plug in this TSB.....

    BULLETIN: 03D-J-171
    LINE: 41
    SERVICE BULLETIN
    TO: ALL DISTRIBUTORS DATE: DECEMBER 12, 2003
    AND JOBBERS
    FROM: S. D. CHRISTOPHERSEN, PRODUCT SERVICE & TRAINING
    SUBJECT: INFORMATION ON NEW SPARK PLUGS AND GAPPING
    MODELS AFFECTED:
    2004 Buick Ranier
    2002-2004 Cadillac Escalade, Escalade EXT
    2003-2004 Cadillac Escalade ESV
    2004 Cadillac CTS-V
    1997-2004 Chevrolet Corvette
    1998-2002 Chevrolet Camaro
    1999-2004 Chevrolet Silverado
    2000-2004 Chevrolet Suburban, Tahoe
    2002-2004 Chevrolet Avalanche
    2003-2004 Chevrolet Express, TrailBlazer
    1999-2004 GMC Sierra
    2000-2004 GMC Yukon, Yukon XL
    2001-2004 GMC Yukon Denali, Yukon XL Denali
    2002-2004 GMC Sierra Denali
    2003-2004 GMC Envoy XL
    1998-2002 Pontiac Firebird
    2004 Pontiac GTO
    2003-2004 Hummer H2
    with 4.8L, 5.3L, 5.7L or 6.0L V-8 Engine (VINs V, P, T, Z, G, S, N, U -- RPOs LR4, LM4,
    LM7, L59, LS1, LS6, LQ9, LQ4)
    PARTS INFORMATION:
    A new spark plug has been released for use in the above vehicles. The new spark plug has an
    Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the
    spark plug has also changed. The new spark plug, ACDelco Part Number 41-985 (12571164), is gapped to 1.01mm (0.040 inches) when the spark plug is made. The spark plug gap is set during manufacturing and should not be changed to the gap required with the Platinum plug, or damage to the spark plug may result.


  10. #10
    Quote Originally Posted by rbob93 View Post
    Only if using the new plug in this TSB.....
    There is more to it than that. The iridium plugs were recommended in place of the platinums at .060" because of THOUSANDS of idle quality issues covered under warranty. I've been installing fresh plugs in C5 Corvettes for years gapped at .040" to solve idle problems. I've done this since talking to a Corvette specialist at a local Chevrolet dealer. He claims this was recommended by a GM field service engineer during new model training.

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    Ngk-tr55, part#3951

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    Member bryceslu's Avatar
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    Well SOB looks like i did know something when i recomended .040-.045

  13. #13
    I use 40-45 thous if i want a smooth idle....55-60 if i want more fuel mileage and a little better throttle response.

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    Slow'er'Ass Mr. Luos's Avatar
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    I gap my TR55's at .050.
    Gapping the AutoLite AR103's the same.


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