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Discussion Starter · #1 ·
I've been researching this topic a lot and have found a lot of good information on this forum, other forums, google, etc. and am trying to decide what plugs I should use in my engine. Anyone please chime in with information, recommendations, etc. as I've gathered all this information and want to know if it's correct, etc.

Heat Range:

I read that switching to a colder heat range plug is recommended if you have the following: A lot of ignition timing advance, high compression, high octane fuel, more power output over stock(I read that you should go 1 heat range colder for every 50-100hp over stock).

How does overall engine temperature effect spark plug heat range, or does it have no effect? For example, stock engine operating temperature is about 200 deg F with the stock tstat. If I switch to a 180 deg tstat does that have any effect on what heat range plugs could/should be used?

Gap:

From what I understand, the larger the gap the better the performance. The problem is you need a lot of spark energy for larger gaps. Too small of a gap can cause detonation. I wonder also, why does the lower bank of plugs in the 4.7L use .050" gap and the upper bank of plugs uses .040" gap? Does this have to do with the material of the plugs (lower is iridium, upper is platinum)? If so, would using iridiums in the upper bank with .050" gap be an improvement?

Material:

Iridiums last the longest, but are the most expensive. Platinums are sort of mid grade for longevity and price, but they can cause engine damage with high performance applications apparently. Coppers are the cheapest but last the shortest. From what I understand, plug material basically has no effect on performance, only duration of the plug...

What I'm wondering is if I should/could switch my plugs to a colder heat range (1 range colder) and if this would be a benefit/no change/bad thing to do. Also, if changing the upper bank platinums for iridium or coppers would be any benefit/no change/bad thing to do (I understand with coppers they'd need changed more often). For example, would running iridiums in the upper bank allow more gap and give more power.

The reason I'm wondering is because I have the tuner which adds a lot of timing advance, I use high octane(93), and I will be somewhere around 375hp-400hp when done (more than 50hp over stock).

Thanks for any input in advance!
 

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Discussion Starter · #3 ·
I've found a lot of info both on this forum and also talking to a guy on a buell forum. He probably has more knowledge than everyone else on the forum combined lol. He's given me a lot of good and helpful information.

The stock plugs are as follows: Upper bank are platinum gapped at 0.040", lower bank are iridium gapped at 0.050".

Iridium plugs are able to run more gap because they have less resistance. Also, they last longer.

The coils on these engines batch fire (fire both plugs at the same time), however, since there is a difference in resistance in the plugs due to different materials, the iridium fires first and the platinum fires a few degrees (of crankshaft rotation) later. For example, the iridium may spark at 30 deg BTDC and the platinum will spark at 27 deg BTDC, even though the coil fires both plugs at the same time.

This is most likely not by accident, but is the result of a lot of R&D and trial and error by the manufacturer. Depending on the manufacturers purpose of using two different plug materials, using an iridium plug in the upper bank may be better/same/worse. If the purpose is to control the flame front and help prevent spark knock, then it may make spark knock more likely if both plugs fire at the exact same time instead of delayed by a few degrees. If the purpose is simply for cleaner burn, better emmisions, then it will likely have no effect.

I will most likely switch both upper and lower banks to a colder heat range. Also will probably experiment with iridiums in the upper bank. If it's no change then I'll put them on the shelf until the lower bank needs replaced again.
 

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Discussion Starter · #4 ·
I think I have a plan.

Anyone that can confirm the oem spark plugs and part numbers?

And what would be even better: Anyone know the same information for the oem plugs but one heat range colder?
 

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Discussion Starter · #5 ·
I made a mistake, the upper bank is not platinum. They are copper core yttrium nickel or something like that. Both upper and lower banks are bosch.
 

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Hmm never was very informed on plugs always just did direct replacement out of fear of something going wrong maybe one day when i do some motor work ill consider different plugs good read thanks guys
 

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Discussion Starter · #7 ·
I'll follow up with my results. I'm going to try the iridiums in both banks at 1 heat range colder. If it's no better then I'm going to switch back to oem plugs but still 1 heat range colder.
 

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Sean, recall watching something on TV (insomnia at 2 am) about flex fuel engines, Octane rating of E85 and how high compression and heat contribute to getting the most out of higher octane, which isn't much.

Now, with that said, here is my disclaimer: I COULD BE WAY THE HELL OFF BASE ON THIS.

You had mentioned the delay in the firing of the top copper plugs and the lower irridium plugs. I'm "wondering", is this to get a more complete burn on the ethanol if someone actually decides to run E85 through their engine?

Example: Top plug fires and ignites fuel/air mixture. Bottom plug fires to complete the burn.

If I remember correctly, the manual states copper on top and iridium on the bottom. I've heard the material provides less resistance, allowing for larger plug gap, resulting in larger spark. I've also "heard" platinum and iridium both last longer.

If this is true, then here is something to consider: The manufacturer was saving money by throwing copper plugs on top. If, as you mentioned earlier, the top fires first, quickly followed by the bottom, based on the angle of the cam, then the type of plug shouldn't matter. The plug is just the light bulb. Something else is hitting the light switch.

I've thought about switching to platinum when I change out the top plugs just to make them last longer. I've heard the bottoms are a real pain in the @$$ to change out.

This is just my thought bordering on theory, based on scientific wild ass guessing.
 

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Discussion Starter · #9 ·
scientific wild ass guessing
I often "SWAG" as well :)

Most of what you posted is along the lines of what I've researched.

I'm not sure what you're comment about the cam angle is getting at. The reason that there is delay between spark with the plugs is because of the material difference. The coil sends the signal to both plugs at the same time, but since one plug is copper and one plug is iridium, the one with less resistance (iridium) will actually fire a few degrees (in terms of crankshaft rotation) before the plug with more resistance (copper). If both plugs were the same material they would fire at the same time. So actually the bottom plug (iridium) fires first.

I do not believe this design has anything to do with ethanol/E85.

There's a lot of high tech theory with flame fronts, I believe the faster the flame front travels the more efficient and more power it produces. I think that's the theory behind dual plugs. Now whether they have two different plugs is because of having them fire a few degrees apart, or if it's due to maintenance costs, only they know. If it's specifically for having the plugs purposely fire at slightly different times, then it may not run as good if it's changed. If it's purely for reduced maintenance costs, it may run slightly better with other plugs, or just the same, or again maybe worse, who knows...

My goal is to give an honest go at this with the research I've done and picking the brains of the knowledgeable people I have helping me, rather than just trying random plugs for no real reason, then assuming oem is the best.

I am 99% sure that just going to the colder heat range will be beneficial to me as I have some mods. If nothing else it should run the same, but be less likely to ping/detonate. That's a good thing. I'll also try iridiums in the upper bank, if I notice a difference for the better then I will leave them. If I notice no difference maybe I'll switch back. If it runs worse or pings/detonates I'll definitely switch back...
 

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I miss interpreted your post. When you used the word "degree", I thought you were talking about something else.

Is it possible to pick the brain of an actual automotive engineer? Maybe get online with Mopar and ask them if this would fly? I'm dying to know this and I'm GLAD you brought this discussion up because I was going to swap out the top plugs at 30,000 miles with platinum or iridium just to make them last longer.

I'll be watching this post for the outcome.
 

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Discussion Starter · #12 ·
I've got a plan, and I know what the proper oem plugs are. I just need to figure out what the correct part numbers are for one heat range colder then I'll be buying them and installing. May be some weeks...
 

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OK, you guys want the skinny? :p Here is the deal. You guys are both right, in a way. The way the engine is designed, It requires 2 sets of plugs to "complete the burn". Plug 1 burns, gets most of the fuel, Plug 2 burns (iridium) and gets whatever is left. They fire ALMOST simultaneously, literally less than 1 degree from each other. It really is a fascinating system. I am not sure which ones fire first on the 4.7, but I am pretty sure it is the coppers. I will have to do some research.

The factory part numbers for the plugs in the 2008+ 4.7 are: Upper Bank — FR8TE2 (Gap 0.039 in [.99 mm]) Lower Bank — FR8T1332 (Gap 0.051 in [1.30 mm]). You can adjust gap to your preference, mine is slightly over on the upper bank, and will be slightly lower on the lower bank when I change those. FR8-TE2 is a Copper Core Bosch, though I am pretty sure Champion makes one as well. FR8T1332 is an iridium plug, good for 100,000 miles or more.

Sean, the way the engine burns fuel, going to a colder range plug, or a plug style like E3 or anything of the sort in the upper bank will not help, but could in fact hurt your engine's performance. At a minimum, I know for a fact in another 30k, you will be paying more for your platinum's or whatever, because the plugs in the upper bank WILL go bad in 30-40k miles, due to design. Its really the only way to run a dual plug setup. One set is gonna burn out fast, and its usually the one that fires first :) If both sets are iridium it throws off the timing of the spark due to resistance, and could potentially screw some things up. I doubt it would do anything major, but you might blow a coil. I know the E3's blow coils on both the 4.7 and the 5.7, because I have put them in, gotten 3 feet out of the garage, and gotten a stumble and misfire in cylinder 2. I put a set of OEM plugs in, changed coil #2, and went on my way with no issues. Had a friend try them in a 5.7, blew 3 coils. :(

I would highly recommend keeping factory plugs unless you have a reason to go colder, such as forced induction/nitrous, etc. The lower bank isnt too difficult to change, with the right tools (a couple of u-joints and extensions will make things easier.


Torque to 22lb-ft (I go to 10, 22 makes me uncomfortable with the integrity of the plug), Make sure you use anti-seize, and use the special tool to pull your coils so you dont rip them. :)
 

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Discussion Starter · #16 ·
Iridium has less resistance than copper/nickel so the iridiums(lower bank) fire first (by a few degrees).

I need to call bosch to find the plugs I want (they have no email support....weird).
 
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