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PS: I've been trying to find one of these type of Spark Plug Gapping Pliers. Best way to close the strap to a tighter gap.
 

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2012 F150 Lariat Screw 3.5L
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The SP 542s are one step colder for the 3.5L. At least they are for my 2012. I'm currently running them at .028 but the next change I'm going to tighten them up a bit to .026; as recommended by my tuner.
 

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If the 550's are just a smaller gap, than I'll run them. As Jordan says, WAY cheaper than the 534's.
I order mine from the US and pick them up at the Shipping Warehouse when I visit friends/family in the Lower Mainland. SP-534s are US$5.99 last time on Amazon.com. SP-542s are US$7.43. If the order is under $75, the border doesn't even make me go in to pay the taxes! In Canada however, everyone wants to rip you off for the Motorcraft plugs. Even Amazon.ca rips you off.

Being an old-time hot-rodder, one of the first things I tried was colder plugs (NGKs at that time ... there were no choices then) once I got tuned. The colder plugs had no advantage and no affect on KR (not like when I installed an CAC). I went back to SP-534s because I found the stock plugs ran better in city traffic (and I have times where I drive pure city for weeks at a time). If a person drives a LOT of city traffic, the SP-534s ran better and had less tendency to foul. (I found a tight gap helped more for a smooth running engine).

If I drove a lot of highway (especially towing), then I would probably run SP-542s.
 
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PS: I am anxious to see what the higher volume GT Turbos do for KR. With the lower boost and higher volume of the GTs, I think that will do more for reducing KR in WOT than a colder range of plug.

I have a fair amount of Datalogs that I can do some good comparisons.
 

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BTW...the 6 SP534's I just ordered from RockAuto came out to be $41.63 shipped. I opted for 2-3 day shipping instead of 10-14 day shipping for an extra $2 dollars.
 

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2012 F150 Lariat Screw 3.5L
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I just picked up a set of SP-542s from O'Reillys for 5.99 each.
 

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I have had great success with:

[h=1]NGK # 6509 Iridium Spark Plug LTR6IX-11[/h]
 

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Ordered some SP-550 today, will pick up tomorrow. From my research and the fact ford now makes them the OEM plug for the newer vehicles and if you go to ford and ask for plugs, they pull up the SP-550 for 10-current eco. They are even offered as an upgrade on most ford racing performance sites.
 
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Yep. And in their office is a bookcase loaded with cartons of that specific plug and a manual gapping device.
I watched them gap me a set.

My motor was too hot to swap out so I promised him I'd do them when I got home.

(my truck had spent the previous few hours on his dyno and HE wasn't happy with how the truck was responding to his tune-tweaks. I, on the other hand was grinning as I watched each pull steadily increase. He suddenly looked over at me and asked "you have our plugs in this thing, right?" I replied "what plugs?"

That ended the dyno session. Lol

Obviously I don't know how much the plugs increased performance since the truck was at home when I changed them. But in theory, there was some untapped output waiting for those plugs. I DO know the truck runs fantastic. Always predictable.)

Sent from my SM-N950U using Tapatalk
So what type of numbers did you pull on the dyno?
 

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2022 Powergrid KingRanch in Sparkle White
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I posted the dyno runs on this thread somewhere back a ways.
Although Matt's dyno is identical to the one I did the tune-comparison, I haven't been back on a dyno since the plugs went in.

Oops, not this thread. The GearHead tune thread. Sorry
 
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