RE: The Great Glow Plug Run Off!
Nice tests!
Did you run a standard cox head also?
Another thing with these adaptor heads is that the lenght of the regular plugs are quite different, this alters both the geometry of the combustion chamber and the compression ration. I'm guessing the volume was measured using the OS plug?
Do you have a pict of the OS plug when inserted in the head?
There still seems to be a loss of 1000 rpm, as compared to the galbreth head, or did I miss something?