GEN 2 Which plug should I go with Sp 550 or Sp578?

Grayson

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I have a set of these (-1 because i dropped one) when I say they are cold natured, I couldn't get the vehicle to crank even with adjusting the gap. This was on a 3.0 Ecoboost which is a nightmare compared the the ease of a 3.5L IMO
 

K-Doob

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SP542s are the best OEM plug, especially if running a tune. Unfortunately they can be difficult to find these days. Last set I had to piece together from local auto stores and ebay sellers.
 

digscruze

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I believe the 542’s were rebranded and are now under a new part number M-12405-35T. There’s a previous thread about that.

Otherwise they’re pretty common to find. SPD Performance and MPT are some of the few that carry them. At the time of this writing, they’re running a sale on them now for under $50 for the set of 6.

 

costnsg

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I am planning to change plugs on my 2017 Raptor with 95,000 miles. Manual indicates change after 100,000, so I'm about there. Unfortunately, the proper plug is a little confusing. My truck is stock, btw.

My manual supplement shows proper plug is SP-534. Online searching for ford parts and the local Ford dealer says SP594. My online searchs indicate the SP594 is a replacement for SP542 and SP578. So, is SP594 the proper plug? I haven't found SP594 mentioned on this forum.

Online and in this forum I have found advice to use 133 in-lbs to torque the plugs. I didn't find a torque value for the bolt holding the coil.

Anti-sieze is another variable, but after reading lots of back and forth about whether to use it, I am leaning toward not using. I expect the torque values are based on no lube. Lubed fasteners will definitely develop more bolt stress with the same torque versus dry, so I expect the same principles apply to a spark plug (probably screws into head a little further with lube vs without).

So, looking for confirmation to use SP594 plugs torqued to 133 in-lbs without anti-sieze. I'd also be interested in torque values for the small coil fasteners if someone has that, otherwise I'll try to be careful with them (not too tight).
 

element217

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