That's really interesting. Running 86 at at altitude should be like running 88, so you're regularly using lower than mid-grade. I'd be very interested in seeing a picture of your sparkies, if you have them handy.
I agree that starting with the easiest thing first is best: colder plug. It would be easy to see the conditions after 100, 200 and 300 miles.
My NGK BCP5ES is running a bit hotter (pitted electrodes) than Bosch F8DC4. I'm going to get BCP6ES for running with 91. So, with BCP7ES, I might be able to run 89 at least without the timing retarding.
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Last edited by jsap; 08-06-2010 at 03:16 AM.
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