I figured that after 5yrs, it was time for new plugs. What to get?
Bottom line. After spending an hour trying to puzzle this out, I bought NGK 7131.
My notes from Chuck Baader said that 1) For racing get a plug 1 step colder than OEM. 2) Good solution is the Autolite AR53.
The AR53 is hard to find and I’m not good at patience. I wanted something I could get either locally, or at worst, a couple days.
There’s a couple ideas as to what plug we’re supposed to be using. The original stuff isn’t available anymore. Bosch now says WR8LC+. Bimmerworld and Turner say W8LCR. The common thread is the 8 which is the # designating a cold or hot plug. And Chuck said for racing do one step cold. For Bosch, that means a lower # so 7. But how to find a plug that is the same, just colder?
The way I figured it out was to go to NGK. The Bosch WR8LC plug corresponds to the NGK ZGR5A. In the NGK world the colder plug is a higher # so 6. That led me to the ZGR6A and BPR6ES. Those don’t get a lot of hits, but if you use the NGK part # for BPR6ES…7131, now you can find them anywhere. I got mine at the local autoparts store.