NGK Spark Plug for 915is?

It's a touchy subject with Rotax when addressing old NGK plugs vs new style Rotax supplied plugs. 

297-656 is the same plug for the 912 UL / ULS, 912iS and the 915iS as listed in the parts section. Same NGK's used by the vast majority for many years. Rotax wants you to use their plugs, but it's your final decision. .

Yes touchy...

  On our field a brand new 912UL install ran very roughly.....until the Rotax fancy plugs were removed and standard NGK's installed !!..problem solved.

I have seen no credible evidence that the duel earth plugs run better or are more reliable.

Clearly personally I will stick to NGK and change them every 100 hr until and if more evidence is presented.

I think the subject nobody wants to touch is the actual NGK Part to cross-reference.
I'll put on the Welding gloves and pass the Hot-Potato with This old post.

I think this is even “extra touchy” when talking about the 915 engine.  The service letters Rotax issued to introduce the new spark plugs were applicable to the 912, 914, 912iS engines. With those engines we had the original NGK plugs to reference if you wanted to keep using them.  I believe the 915 has always been delivered with the new Rotax plugs, so if selecting an alternate plug you would be doing so on your own. I’m thinking that it could even void the warranty.  If it were me, I would use the Rotax’s plugs for a 915.  

Like many things in life you have to make choices. I'm definitely a researcher and analytical person so when I make a decision I like science and testing to back it up and not just Joe Blow's opinion from next door. I do believe sometimes there is more than one way to skin the proverbial cat so long as the end result is the same and you do not cause issues.

I like all the info good and bad to make good decisions. Sometimes it can be a coin toss, but you should always try to fall on the right side of the fence.

The older NGK's were NGK DCPR8E plugs for the 912ULS and NGK DCPR7E for the UL. Then Rotax went to one size fits all. NGK bailed due to liability not performance. Actually there is a little picture on the NGK box that shows a line through an aircraft as a do not use symbol.  Bosch makes the new plug with the Rotax name. So when the newer 912 series engines and 915 came out they all now have the Rotax plug. They encourage the use of the Rotax plug and the Rotax service centers are only supposed to sell the Rotax plug.

I hope I don't get a letter from Ted Kaczynski. LOL ?