UPDATE: NGK website has bad info on it, see post below from Robby363 that get it right. Info on Cabin Air Filter is still useful

I've been doing some data gathering trying to figure out some maintenance parts for my SRT-6 and I happened upon the follow discrepancy between SRT6 and SLK32 spark plug specifications.

Ignoring the difference between the "I" and "P" at the beginning, which denote Iridium and Platinum respectively, the SRT6 plugs call for a 5 heat range with a 0.044" (1.1mm) gap, while the SLK32 (and C32) plugs call for a 1 step colder plug with a 0.040" (1.0mm) gap.

SRT6 - PFR5R-11
SLK32 - IFR6D-10

Anyone know why Chrysler specified hotter plugs with a smaller gap than Mercedes did for the C32/SLK32? Increased service interval? Something to do with pollution control? Reliability?

Is this a clue to often debated (but not yet put to bed, I think) debate on why Chrysler rated this powerplant at 19hp less than MB?
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A good looking part deal I found poking around the web :

GermanAutoParts has a great price on the OEM Micronair Cabin Filter - I paid almost as much for the WIX, and its construction wasn't anywhere near as impressive as the OEM Micronair filter.

 

The ones NGK has listed for the SRT6 are for the na Crossfire. The plugs for the SLK32 AMG are the right ones for the SRT6. Check the owners manual and you'll see they are the same I think NGK made a mistake on their site.

 

You are correct!
Owner's manual confirms IFR6D10 as the correct plug.

Darn, I missed something obvious. Bad assumption on my part that NGK would have good info.

Even worse is that the bad info on plugs has leaked all over the web though EDI.

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I deleted the screenshot from the NGK website so as to avoid future confusion.

 

-6 is recommended for stock and mildly modified SRT6. Some MB owners prefer the -5 for better fuel economy (this is what i have read, there are a lot that agree with this). The -7 are for more modified vehicles.

Both LET and I carry NGK if you need them.

 

Maybe we should tell NGK they need need to correct the the info they have.

 

Good idea!

I called their technical support line, described the problem, the tech who answered acknowledged the mistake and he said that he would report it to cataloging to update the cross reference.

He also said that the NGK website was run by a third party, so it might take until the next bulk update before it was fixed on the web.

Sadly, he did not offer me a free set of plugs for my trouble