Gx390/Gx 440 Spark Plug

Use an NGK standard plug they can't be beat and there are not any gains to be made by spending 2 or 3x as much money.
 
I like the NGK BP6ES (notice no R). That's what I like to run regardless of build. Remember a BP5ES is a little hotter, a BP7ES a little colder plug Lower number=hotter, higher=cooler. That's in a NGK, not other brands typically.
 
I run a BPR7ES, but I'm on the asphalt for 12-15 minutes and we built a bit more heat therefore the colder plug. I change my plug cap out to a regular silicone one and run the R plug for reliability. While the non-R plugs work fine they can cause interference with scoring systems and such.
 
rkcarguy said:
I run a BPR7ES, but I'm on the asphalt for 12-15 minutes and we built a bit more heat therefore the colder plug. I change my plug cap out to a regular silicone one and run the R plug for reliability. While the non-R plugs work fine they can cause interference with scoring systems and such.
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I think the compression ratio should be taken into consideration when choosing a plug. A stock, clone, with its 26 1/2 cc head could run a hotter plug than an engine with less CC's. How many CC's in the combustion chamber of your engine?

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Al ...not sure We run these as claimers...Only thing I have done is set valve lash. They are supposed to be 10.5 to 1...They do have a flat top piston instead of dish. I gapped the bpr6es @ .030 and it seemed to run great, haven't pulled the plug to take a look at it yet.
 
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