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The dead horse gets kicked one more time: Spark Plugs

This is a discussion on The dead horse gets kicked one more time: Spark Plugs within the General Help forums, part of the LSx Technical Help Section category; After switching to the TR5 IX iridium plugs (NGK), I noticed an improvement in my fuel economy (about 40 miles ...

  1. #1
    Senior Member Naaman's Avatar
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    The dead horse gets kicked one more time: Spark Plugs

    After switching to the TR5 IX iridium plugs (NGK), I noticed an improvement in my fuel economy (about 40 miles more per tank). Because of the new heads I've got, the compression is slightly increased and so I had to go with TR6 plugs. I asked for the same style (IX iridium), but Sean told me that NicD says I need copper plugs because they fire better (or something).

    I thought I understood spark theory (flame expansion, atomization, stoichiometrics, etc.), but now I am confused. Based on what I though I knew, if a spark plug COULD improve fuel economy, I would have thought it would be due to a more complete burn (better, fatter, hotter spark, for example). NGK even claims that the IX iridium will yield better fuel economy (and also says it will yield the same amount of "performance" as a copper plug).

    The only other thing I can think of that would alter fuel economy (besides spark "quality") is the duration of the spark, but that is based on the ignition module/coil set up, not the plugs, right?

    Can anyone shed some light on this?

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    Veteran 0rion's Avatar
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    iridium and platinum plugs are designed primarily for extended life.......they're an alloy with copper in them. Why copper you ask? Because copper is a far better conductor than either iridium or platinum. A better conducting plug is what you want if you're talking performance so a copper plug is the way to go. If you're looking to get a lot of mileage out of your plugs then iridium is your better choice. Everything else is marketing. There really is a ton of mis-information out there on plug materials and it gets confusing. Always remember....copper is more conductive but iridium and platinum are harder. That should tell you most of what you need to know about any plug and it's purpose.

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    Spaz is My Mentor SMWS6TA's Avatar
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    to add on to what Orion posted...

    Hard core track motors use copper plugs for a few passes and then changed out. So using them long term is not in consideration. NGK's are good for 25-30k miles for normal driving with medium track use. Using N2O and you'll be in a different plug like a TR6 depending on the heat range. And again depending on how hard you spray you could be doing plug changes at the track.

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    Senior Member JayTA98's Avatar
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    In my case I used to get platinums or iridium because they lasted longer so I won't have to change them that often. I never did any racing just DD.

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    Senior Member Naaman's Avatar
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    But how do I account for the improved fuel economy I experienced with the IX Iridiums? This plug out performed the TR55 and the Autolight equivalent in fuel economy. With either of those two plugs, I was seeing 280-290 miles on a full tank of gas. With the TR5s, I could regularly get over 320 miles out of a tank (went as far as 335 once). It was repeatable with every tank of gas. Same driving habits (hard acceleration on on-ramps, occasional bursts after red lights on an empty road, etc).

    From the time I bought the car, it's had two sets of TR55s and one set of Autolites. Mileage was the same with each plug change. The TR5s instantly improved my economy by an amount that is impossible not to notice.

    This is what's confusing me. The data is there. I'm just at a loss as for how to interpret it.

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    Senior Member Naaman's Avatar
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    So I've been tracking my fuel economy since the new build. It seems that my city mileage is pretty much worthless, and my highway mileage is about the same as with the TR55s. There are several things that need to be considered, of course.

    First of all, its a different engine (from an 01 bird).
    It's also internally modified (duh).
    It's also tuned. Looking at the dyno, the richest it ever runs is in the 13-ish range. Never gets any leaner than the 15s. I remember in school, I did the sniffer test at idle, and the stock tune had it running as lean as 18:1 at idle. So, all that considered, I realize that my fuel economy could be different.

    I'm going to try a good number of tanks of gas on these copper plugs, and might just get a wild hair and swap to the IX Iridiums to compare. I figure 20 fill ups or so ought to do it. Maybe around the first of next year I'll swap the plugs and try the experiment. On the other hand, at the rate I'm using gas, I might get through 20 tanks by this fall.

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    A lot of times, a perceived improvement in fuel economy may be attributable to the fact that there were worn parts or other issues that had caused a drop in the first place. Your engine may actually be getting the same fuel economy it always did with good plugs, but now it is just back to its prime with the new plugs installed. You are talking about a 2-3+ mpg increase if my math is correct.

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    Senior Member Naaman's Avatar
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    Quote Originally Posted by pajeff02 View Post
    A lot of times, a perceived improvement in fuel economy may be attributable to the fact that there were worn parts or other issues that had caused a drop in the first place. Your engine may actually be getting the same fuel economy it always did with good plugs, but now it is just back to its prime with the new plugs installed. You are talking about a 2-3+ mpg increase if my math is correct.
    Yes. On the IX Iridiums, I saw 24 mpg regularly. I just did my first fill up on the new build. It was 21 mpg. One of my "markers" is the miles driven upon consumption of the first 1/4 tank. On the old plugs, it was typically 120-130 miles. On this tank, it was right about 100 miles. 100 is consistent with the mileage I was seeing on the first two sets of plugs (TR55s and Autolites). Those two sets of plugs account for about three years worth of data. The IX Iridiums boosted that number to at least 120 every single time (fill ups once a week for about 18 months).

    That section in bold is exactly what I'm trying to rule out. If I can't, I figure it may be worth while to switch back to the IX iridiums and others may be able to benefit from the data as well. (Incidentally, I've looked under my hood and even though the EGR is gone, that number 8 plug still looks like a PITA to get at... I may try it myself to save some money... we'll see).

    So, based on what I've seen so far, the copper plugs are "just as good" as the TR55s and Autolite platinum (or iridium, or whatever they were). But the IX iridiums by NGK seem to be somehow "different" from the other iridium plugs they offer.

    Looking at the NGK website, they have 2 different iridium plugs for our cars.

    There is the laser iridium and the IX iridium. They rate various aspects of the plug's performance for comparison.

    Copper $2.89
    Performance 2.5/5
    Durability 3.5/5
    Fuel Economy 1.5/5
    Life Span 1.0/5

    Laser Iridium $9.23
    Performance 2.5/5
    Durability 3.5/5
    Fuel Economy 1.5/5
    Life Span 4.5/5

    IX Iridium $7.83
    Performance 3.5/5
    Durability 3.5/5
    Fuel Economy 2.5/5
    Life Span 2.0/5

    G-Power (Platinum Center Electrode, Nickel Ground Electrode) $3.15
    Performance 2.5/5
    Durability 3.5/5
    Fuel Economy 2.5/5
    Life Span 1.5/5

    I'm not really sure what "performance" refers to, but, whatever.
    Lid, Throttle Body, LS6 Intake, Heads, Cam, Magnaflow, LS7 Clutch, SFCs, STB, Panhard Bar, Strano Springs, Hollow Sway Bars, Poly/Roto LCAs, Konis, MGW Shifter

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    Try a go at the infamous "No. 8" from under the car.

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    Senior Member Naaman's Avatar
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    I will. I've tried it once before from under, but didn't do so great (it was on jack stands... might have been easier with a lift). In any case, I'll start with number 8. If I can't get at it easily enough, I'll just leave it alone or wait till I have time to muck with it.

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