Firestone Spark Plugs

[SANTA Ray]

I know there were many aftermarket plugs available. I found this NOS set of four SH-110 Firestone plugs. The business end looks like they will fit a Modle A and the threads match. Does anyone have any information about these? Can they be used in an "A"? Are they standard heat range? All are in great shape. Do they have any vaue?

 

[Gary WA]

I have some Firestone Polonium S-120-Cf But not in use tho!!! They look nice Value???

 

[pat in Santa Cruz]

I had a set of Firestone S-40-CF in my old pickup. They were a touch on the cold side for that engine, which was stock and old. Their insulator was positioned about the same as the Autolite tt10. Without a chart giving heat range,its hard to say, but if you can post a pic of the tip, so we can see the length of the electrode and insulator, someone here can give you an idea if its a hot or cold plug. Your best bet is to run with them a bit at driving speed, shut off the engine and coast to a stop. Then pull them and read the insulator color to see if their heat range works in your engine. If they're too hot, they'll be whitish and crusty; too cold, black and sooty; Just right, a tan/brown