I wonder with three years of miles what the threads beyond the plug look like, could you get the correct plug in or is there carbon at the ends of the threads that might fall into the cylinder. i don't know, just asking.

 

I had something similar happen with my first Cosworth Vega. The Cosworth plugs have a much longer reach than the regular Vega plugs that the previous owner had installed. I greased up a spark plug thread chaser to catch the trash and cleaned the threads up before I put the new, correct plugs in it. No problem.

 

I'd run a plug chaser in first to get all the carbon out of the threads and not have maybe a plug stick/strip. Can find them at auto parts store and found one even at my local Ace.

 

It will run better and probably need less advance. Better fuel economy for sure, but how much is only a guess.

 

...probably need less advance.

Interesting.
Does that mean I might get "pinging" if I leave the timing as is?

 

Your overthinking it. Just screw them in slowly, then out, apply some antiseize then screw them back in. Done.

Anything on those threads is stuff that would enter the cylinders anyway. Oil residue and rust that if is on there has been washed by fuel and flames under pressure and not going anywhere.

 

Spark will be closer to the center of the chamber, hence it will light off the fuel quicker which implies it will need less advance.

No guarantee on that, but it seems logical to me that it would need less. Whether that is a 1/2 degree or 4 degrees, I would not know.

 

Before I installed my Vortecs I read on another forum that spark plugs were different. I'm currently using AC R42LTS with good results. If your compression is higher, you might want to go a little colder with a 43 or even a 44.

 

Ok, thanks.
When i rebuilt the engine I used extra thin head gaskets .016" to bump up the compression a bit.
Engine has stock flat top pistons, and based on that my theoretical compression should be 9,9:1.

I have ordered Champion 401 (RS12YC) spark plugs. Hope that's not way off?

 

Very curious to see how this turns out in terms of tune and performance changes/differences.

 

I'm afarid I won't be able to test this until next summer.
Hot rod season is over here in Norway for now, and it's time for "the usual winter upgrades" that always turn out to be much more than planned!