Let's talk spark plugs...

3191 Views 15 Replies 5 Participants Last post by  snrusnak
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?


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?


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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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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