I've installed a 15% underdrive SC pulley on my MC40. I understand that I should be using a colder plug and am looking at the NGK BKR7EIX but also understand they may be a bit longer than stock. Anyone running these? Should I be concerned with piston clearance? Any suggestions?

 

I got these and installed them. They work great! https://www.rockauto.com/en/moreinfo...=1041272&jsn=1

Edit: Oh and I also have a 15% reduction SC pulley, and 2% increase Crank pulley.

 

#Hecka, thanks for the reply. The plugs you're referencing are run on the JCW version (which should work on mine as well) and, if I'm not mistaken, are the same length as stock. The Iridium plugs are 1mm deeper from what I've read and I'm just trying to be cautious and find out if there are any clearance issues. Anyone running the NGK Iridium plugs (#7 range) in an R53?

 

Yep, ~10k (mostly) trouble free miles. I did blow a spark plug out of the head, but I don't think it was NGK's fault.

 

Been running the 7 Iridium for years

 

We only recommend using the OEM JCW platnum cold heat range plugs with the pulley install.
https://www.waymotorworks.com/john-c...gs-by-ngk.html

We do NOT use Iridiums with our pulley kits as we have found them to not last as long, and also commonly come loose. And if they come loose can easily blow out with the threads in the head. I can't tell you how many times we have replaced aftermarket plugs with the JCW and fixed the car. The Iridiums are cheaper so people often want them and we even sell them, but still not recommending them
https://www.waymotorworks.com/ngk-ir...-cooper-s.html