[meknized]

Hello,

I have a question on some spark plugs. I have the GT-40X heads on a 331. I was just changing the spark plugs which are autolite 764's. It has been at least 3 years since I have changed them. One of the plugs in back on cylinder 4 was a champion RS12YC and the other 7 were the 764's. I remember after pulling them that I had broken one of the plugs and that is why I must have put the champion back in. The problem is, is that the autolites have about 3/8 long thread section that goes into the head and the champion have 5/8. I guess I didn't compare them when I had them out. Are the autolites I have been running not reaching in all the way into the combustion chamber? So I need to know if I need a long treaded plug. I can't get my head down far enough to see.