Okay, thanks. So the difference in plug numbers is just what they come gaped at?

 

I swapped mine out for NGKs about a year or so ago.
MPG instantly went up - truck runs great!

 

Not always, but the only difference between 542's and 550's is the gap. The 542's are a colder heat range.

 

I am curious about the plug swap that bronson suggested but I want to see some info on it. Not just "do it because a few other guys have".

 

Well @bronson sherrill, going to post any info on your alternative plug swap? I tried google searching and only found vendors selling the plugs. Nothing about swapping them into 3.5L's

 

Quite a few people on fordraptorforum.com run the 542's in tuned 3.5 H.O. Ecos.

 

Thanks. I found a thread. http://www.fordraptorforum.com/f261/sp542-thread-60306/

 

Okay. Question on gapping

I picked up 6 SP534 and they were all gapped at .030 out of the box. From the various threads I read, I was expecting the gapping to be all over the place.

Or is the poor gapping in the original set installed from the factory?

I will be measuring the gap as I pull each original plug for curiosity.

Thanks

 

I just replaced my plugs with new Motorcraft plugs and was surprised at how poorly the electrodes were set, not straight, each one looked different, bends were different, and the gaps were small and varied. They were brand new, at least four in the original four pack box and two individual. No fingerprints, etc, not returned and restocked. Just poor quality from Motorcraft.

Set them to the right gap and installed them, and they work fine, but wasn't impressed with how they came out of the box. I wonder if Motorcraft doesn't get by with a lot because of the name.

I've bought NGK in the past and they were preset correctly and looked great straight from the box.

 

I've bought 4 sets of SP 534's and they all came gapped @ .030 I recently bought some SP 550's and they all came gapped @ .028