Originally Posted by
cdelong
the length of the body would probably have a small impact on compression ratio as well.
i tend to stick with the F short body plugs since that is what comes with my .21 on-road engines. if you stick a long body (C) plug in there, you are raising the compression marginally.
Definitely wrong. The main difference between the 'C' and 'F' is on the height of the part that protrudes
over the button (in more graphical terms: the height of the hex you use for tightening) and this is what makes their difference in heat transfer from the combustion chamber to the air.
A 'C' and 'F' plugs protrude the same on the combustion chamber, so the compression could not be different between them.
Being conical at the end of the combustion chamber, you cannot insert more the plug unless you do a gorilla tighten and break the plug button or strip the treads.