<VV> ac spark plug identification

[Michael Kovacs]

 I thought I had a listing of the various AC spark plug types. But cannot find it. Can anybody supply me with the meaning of F, FF, S, N, M, etc? I want to run a colder plug in my Fitch.  Either 42 or 43 but need to know which prefix, or suffix will be the equivalent of a 44FF. I guess it would be a 43FF or 42FF to be perfect, but what 42 or 43 would be acceptable?
   
   Any opinions on extended tips vs regular tips? This application is for a rather high compression 140 with the step cut down and .032 copper gasket. It occasionally knocks (3-5 times) on initial acceleration from a gentle start when hot and will run on sometimes after shut down, so I suspect a hot spark plug. Changing plugs is a simple test for a cure.
   
   Any body have a set to sell? Contact me off line for any for sale.


MIKE KOVACS