We usually run 8s. We ran B8EV spark plug even racing TT nationals. If the sharp edges on the ground strap or the electrode began to erode and round off then go to a colder plug. I have run B7's but prefer to run B8's. B9's usually look too cold to me when I check the plug. Next time I dyno test I will run B7ES, B8ES and B9ES. I don't expect to see a power difference, how ever I don't think I have ever checked that.
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