both plugs are resistor type thats the 'R' and the same heat range the 'EYA' is an antifouling electrode and if you have ever fouled the 'ES'the 'EYA' useually solves that trail side plug change. I have used both and it is harder to foul an EYA ,you have to really try them in your sled to see,also make sure to use solid terminal type.
When Cat started using the BR9EYA they talked about it at the race school. The EYA has more surface area on the electrodes due to the grooves, so that reduces the chances of fouling. They also said the EYA is about a 1/2 step hotter than a BR9ES.
So is it OK to use the ES...ask the dealer (Nielsens, again) to give me a box of plugs with my new ZR800 and didn't realize til later that he gave me ES, and the sled calls for EYA. Will I hurt anything by using the ES's, since I have a box of them now?
I had a very hard time finding BR9EYA plugs to carry as spares (most auto parts stores don't carry them yet). Talked to my dealer, and he said the only difference between them is the split in the electrode the EYA has. He also felt that the EYA burned just slightly hotter than the ES. Also, EVA plugs can be used (as long as they're BR9). I think that is a plated plug, not sure with what though. Bottom line, as long as it's a BR9, you can use it, regardless of the letters after.
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