I am running a slightly street ported NA. engine has just about 10k miles since rebuild and 180k total. I run premix, 8oz per 14 gallon with no oil injection.
I average 17 mpg

I switched to running denso s-31a plugs and noticed a decent shift in performance.

question: how do the plugs look to you?

the trailing plugs look cold, and I plan to switch over to the hotter s-29a plugs.

the leading plugs seem to have a lot of carbon build up, maybe from excessive premix? I am running 8oz per 14 gallons which is low already, but though about running even less premix. any thoughts?

thanks!

 

dont you mean the trailing have the carbon buildup?

 

Yes it does seem like the trailers have more carbon buildup than the leads.
I didnt know Denso made a plug for our cars.

 

Those plugs look pretty good to me.

 

brown-ish color is what you should ALWAYS look for.

so yea change trailing one to 1 step hotter and you should be good.