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Spark plugs

This is a discussion on Spark plugs within the External Engine forums, part of the LSx Technical Help Section category; Originally Posted by proud1 ok due to any of my auto part stores not having NGK I bought the AC ...

  1. #21
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    Quote Originally Posted by proud1 View Post
    ok due to any of my auto part stores not having NGK I bought the AC Delco's but question is what gap should I go with there the iridium plugs
    I think the Delco Iridiums (41-110) are factory gapped at .040 and not intended to be gapped by hand, though I don't know why a gapping tool would cause any damage.

    I've had them in a variety of V8 engines (Silverado + Lacrosse Super + Trans Am) and have been completely satisfied.

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    Quote Originally Posted by Wesman View Post
    I agree about the AC Delco Iridium plugs, they are excellent.

    However, I do not agree with your theory of .54 creating a "hotter" spark.

    Spark gap is about the flame front and ignition system voltage. High voltage systems (such as the LS1 coil-over-plug system) can jump larger gaps due to the higher voltage. So by expanding the gap, you get more exposed flame between the electrodes, resulting in better combustion. A gap such as .060 is not possible with conventional distributor ignition systems, because the spark is not strong enough to jump such a large gap.
    I hear what you're saying Wes, but if the gap is larger is'nt there more reluctance for the spark to make the jump? Ie. when a spark sometimes make's the jump to the side rather than the grounded electrode because the distance to the side maybe shorter, which is bad of course, but electricity in high voltage situations is always looking for the easiest or shortest path.. From experiance with long wired plugs, I've had a larger gap actually reduce performance.. While I'll admit, they prolly had cheap gas in some of them, but on the same motors/ same gas with the gap @ spec or even sometimes slightly smaller performance improved to @ least I'd say factory levels... I dunno maybe I'm crazy.. I've also had some that lost mpg's with a larger than usual spark gap. My guess is, (because I can't see in there) with the gap being over sized, the fuel may have been actually momentarily grounding a plug here and a plug there or momentarily fouling them prolly happening just before the plug fires but ending in the middle of the spark ignition as the fuel quickly (faster than we can see) burns off due to heat and evaporation.. I'm thinking this leaves the tail end of the spark to burn the fuel in the chamber causing a "late" flame front ie: the shorter the jump the faster the ignition and a quicker more explosive flame front.. Of coures too small and fouling returns..
    Last edited by Smittro; 02-12-2010 at 12:08 PM. Reason: Can't spell to save my life, and appearantly reading ain't for me either.......
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    Oh and I also noticed that on some of the cars a larger gap caused a small increase in the time it took the motor to fire up @ start up. Which is harder on the starter but it was'nt anything that overly concerned me. However I run a slightly smaller gap in the Camaro and engine ignition is immediate and precise everytime.. May not be much of a big deal but I like when I literally bump the key and she's running.. Start ups are actually faster/better now @ 80k+ than when I baught her with only 26k+ish on the clock.. But as I said the difference is minute and I'm anal
    Last edited by Smittro; 02-11-2010 at 10:14 PM. Reason: Because I'm sitting on my brain....

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    Junior Member WS6 > SS's Avatar
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    All of these facts and theories are fantastic. However, for a naturally aspirated LS1, give or take some bolt ons, Im pretty sure the guys at GM knew what they were doing.

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    Quote Originally Posted by WS6 > SS View Post
    All of these facts and theories are fantastic. However, for a naturally aspirated LS1, give or take some bolt ons, Im pretty sure the guys at GM knew what they were doing. Click for full size
    Yeah I got the manuals too. But I was talking about going +/- beyond spec. As a personal prefference I like things exactly IN spec.. I was'nt questioning you or the abilities of GM.. Moreover a compairison of the max and the min gap allowed for combustion to take place, with the "spec" gap being the neutral or control... The time between the ignition of the plug and when/where the flame front begins..
    Last edited by Smittro; 02-12-2010 at 12:16 PM.

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    Junior Member WS6 > SS's Avatar
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    Quote Originally Posted by Smittro View Post
    Yeah I got the manuals too. But I was talking about going +/- beyond spec. As a personal prefference I like things exactly IN spec.. I was'nt questioning you or the abilities of GM.. Moreover a compairison of the max and the min gap allowed for combustion to take place, with the "spec" gap being the neutral or control... The time between the ignition of the plug and when/where the flame front begins..
    Gotcha. Wasn't trying to offend anyone, just stating the obvious.

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    Quote Originally Posted by WS6 > SS View Post
    Gotcha. Wasn't trying to offend anyone, just stating the obvious.
    No harm done..

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    Just wanted to chime on the heat range of spark plugs. Hot vs cold has nothing to do with gap. It has to do with the plug retaining heat in between the firing sequence. More or less ceramic insulator is what effects heat range. Keep a stock LS1 at .060 gap for best performance. Wider gap means more flame front = better combustion, as long as the coils are in good working order and compression is stock.
    If you really car this much about spark plug flames, start indexing you plugs and then all flames will be perfectly lined up in each cylinder.
    Really does not matter in a stock engine !!!!!!!!!!!!!!!!
    Last edited by NVRANUF; 02-13-2010 at 12:09 PM.

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    Quote Originally Posted by jagfan93 View Post
    I think the Delco Iridiums (41-110) are factory gapped at .040 and not intended to be gapped by hand, though I don't know why a gapping tool would cause any damage.

    I've had them in a variety of V8 engines (Silverado + Lacrosse Super + Trans Am) and have been completely satisfied.
    Document ID# 1396703


    --------------------------------------------------------------------------------


    Subject: Information on New Spark Plugs and Gapping #03-06-04-060 - (10/24/2003)



    Models: 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)




    --------------------------------------------------------------------------------

    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, P/N 12571164 with AC Delco P/N 41-985, 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 or damage to the spark plug may result. Any new spark plug found to not be properly gapped should not be used.



    GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
    WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


    © Copyright General Motors Corporation. All Rights Reserved

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    you get to the back plug on the right side from underneath .

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    Quote Originally Posted by garygnu65 View Post
    you get to the back plug on the right side from underneath .
    found that out after 10 min. of trying to reach it from the top but my arms were to short then taught about it and lifted car up and there it was no problems after that

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    Quote Originally Posted by garygnu65 View Post
    you get to the back plug on the right side from underneath .

    With manifolds -- access from the bottom makes it a 2 minute job to change out Number 8. With headers -- it is probably easiest from the top, although you can still get at it from beneath. This probably depends on the brand and style of the headers though. To be honest, I was expecting it to be much more difficult than it was from what I had read on here. The key to the operation is removing the coil packs as it gives you a lot more room to work.

  13. #33
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    Quote Originally Posted by Smittro View Post
    I hear what you're saying Wes, but if the gap is larger is'nt there more reluctance for the spark to make the jump? Ie. when a spark sometimes make's the jump to the side rather than the grounded electrode because the distance to the side maybe shorter, which is bad of course, but electricity in high voltage situations is always looking for the easiest or shortest path.. From experiance with long wired plugs, I've had a larger gap actually reduce performance.. While I'll admit, they prolly had cheap gas in some of them, but on the same motors/ same gas with the gap @ spec or even sometimes slightly smaller performance improved to @ least I'd say factory levels... I dunno maybe I'm crazy.. I've also had some that lost mpg's with a larger than usual spark gap. My guess is, (because I can't see in there) with the gap being over sized, the fuel may have been actually momentarily grounding a plug here and a plug there or momentarily fouling them prolly happening just before the plug fires but ending in the middle of the spark ignition as the fuel quickly (faster than we can see) burns off due to heat and evaporation.. I'm thinking this leaves the tail end of the spark to burn the fuel in the chamber causing a "late" flame front ie: the shorter the jump the faster the ignition and a quicker more explosive flame front.. Of coures too small and fouling returns..
    What you are describing is a condition in which the spark is not strong enough to bridge the plug gap. As you mentioned, this could be caused by a number of things, such as longer, higher resistance wires, insufficient voltage from the coil, or poor conductivity between the rotor/cap (distributor systems). Spark "blowout" is also another condition that may appear on forced induction or high compression engines, where the cylinder pressures as so high that the spark cannot jump the gap.

    The reason you've seen reduced performance from higher gaps is likely because the spark wasn't completing its path through the ground electrode. Perhaps there was excess resistance somewhere, or perhaps the coil just wasn't strong enough. Either way, such a condition will most definitely result in reduce performance and poor fuel economy.

    As I stated earlier, you want the largest gap possible while still ensuring that the spark is strong enough to complete the gap under all conditions. GM determiend that gap to be 0.060, or .040 for the newer plugs.

    I can tell you from personal experience that you shouldn't have any issues with a .060 plug gap. My car started missing at lower RPM's a while back, and when I pulled the plugs, there were all gapped between .070 and .080 due to gap erosion. The plugs were in there from the previous owner, so i had no idea how many miles were on them. And even with multiple plugs at .080, there was no misfire codes, just a noticeable miss under a load at lower RPM's.
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    Im runnning at .045. Its all i had at the time of my header install. Just wanted to know if this is ok? wont hurt anything will it? Gas milage or anything like that? no damage or anything? If its that trivial ill take em out and gapem to .054 or even .060. NOw that i got headers in there, they are pretty easy to get to.

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    Ok so now im confused....so now GM says that the gap should be .040, but just for iridium plugs??

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    um ok.... some am i now. I have iridium plugs.

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    Quote Originally Posted by bryceslu View Post
    Ok so now im confused....so now GM says that the gap should be .040, but just for iridium plugs??
    Until recently, platinum was considered the best material to use on the top of an electrode because of its durability. However, Iridium is 6 times harder, 8 times stronger, and has a melting point 1200 degrees higher than platinum. Put that into a harsh environment such as an engine piston chamber, and you have a spark plug that can resist wear much better than platinum. Additionally, the Iridium Power alloy is so durable; it allowed engineers to produce the world’s smallest center electrode (.4mm) which reduces the voltage requirements, concentrating its sparking power. When lowering voltage requirements, you dont need as big a gap to get the most efficient spark.

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    Quote Originally Posted by bryceslu View Post
    Ok so now im confused....so now GM says that the gap should be .040, but just for iridium plugs??
    You are correct. .040 for just the iridiums.

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    Ok, so then im fine if i gaped my plugs at .045 since they are iridium. They kinda came that way, the only gage big enough at the time of my install was .045 and I only really had to adjust like 1 or two of them. The rest were already at .045. Just wanted to make sure they all where at the same gap. I myself havnt noticed anything negative having them gapped at .045. My old plugs were horrible. They must have been the originals. They must have had a gap of like 1/16" lol they were burnt bad. THe car ran fine, but it was time for new plugs. glad i swaped to new ones.

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    Quote Originally Posted by JoshuaGrooms83 View Post
    Ok, so then im fine if i gaped my plugs at .045 since they are iridium. They kinda came that way, the only gage big enough at the time of my install was .045 and I only really had to adjust like 1 or two of them. The rest were already at .045. Just wanted to make sure they all where at the same gap. I myself havnt noticed anything negative having them gapped at .045. My old plugs were horrible. They must have been the originals. They must have had a gap of like 1/16" lol they were burnt bad. THe car ran fine, but it was time for new plugs. glad i swaped to new ones.
    I am confident you are gonna be very happy with the irridium plugs. If I remember correctly, the irridium plugs I had came pre-gapped at .040. Pull your plugs at 5-10k miles and see what kinda condition they are in.

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