Question on Champian C-7 plugs

Unknown

Evening all,

I'm starting to investigate my newly acquired 29R parts car just received from the Montana desert.



The engine has Champion C-7 plugs with the electrodes set for side firing instead of top firing. All plugs have a very thin coating of dark combustion residue - like it was burning rich when last run. The mileage on the odometer is 61k. I'm curious as to age since last plug install. Does anyone know when Champion changed their C-7 electrodes to to firing? I'm trying to date the engine's last run. The engine number is different from the VIN tag number too.

Thanks

Jack