[tubman]

Well, wrong again. I tried some "L" series Champion 1/2" reach plugs in an unmolested Offenhauser head and it came up a full 3 threads short of filling the hole. The attached pictures show the head and the plug, both by itself and screwed into the head. The only plug I had was used, so it's kind of hard to see from the combustion chamber side, but it's definitely short.

This whole thing is staring to bring back memories of the early sixties when I drag raced a '36 Ford in "D/Altered". My buddy's dad at the time could get us any plugs we wanted (as long as they were Champions). I vaguely remember fitting various plugs into our heads until we found something where we liked the fit. I seem to remember something about a Champion "N" series which have a 13/16" reach, but that's even longer. Just for shits and giggles, and because it's so easy, I just ordered a Champion N5C from Amazon.

I cannot believe that the original engineers at Offenhauser designed a high performance head that no commercial plugs fit, but it's beginning to look that way.

I'll be looking for another set of Edmunds heads after this.