RCJ6Y
RCJ7Y
RCJ8Y

Do the different numbers indicate different heat ranges?

If so, which would be the HOT plug and which would be the COLD plug?

Or am I just WAAAAY off here?

When would it be appropriate to use a Hot or Cold plug?

I fly at about 4200-4500' elevation and am using Zenoah G-45, G-62 and GT-80 engines and a Fox 3.2 engine. I run pumped gas--87 octane. I run all my engines on non-synthetic oil at 40:1.

Thanks