Let's talk spark plugs...

3205 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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From what i have read on either this forum or another, ( and this could be a load of bull) either the upper or lower is plain copper plugs and the other is platinum.
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