this is from Graham Bell's Two Stroke Performance Tuning... (http://www.kreidler.nl/artikelen/per...raham-bell.pdf
) looks like he's down with the center fire head...
...Researchers have found that it is the gases at the very outer limits of the
combustion chamber, called the 'end gases', that self-ignite to cause detonation. These
end gases are heated by the surrounding metal of the piston crown and combustion
chamber, and also by the heat radiating from the advancing spark-ignited flame. If the
spark flame reaches the outer edges of the combustion chamber quickly enough, these
end gases will not have time to heat up sufficiently to self-ignite and precipitate
detonation. Herein lies the key to prevent detonation — keep the end gases cool and
reduce the time required for the combustion flame to reach the end gases.
The most obvious step that would satisfy the second requirement is to make the
combustion chamber as small as possible, and then place the spark plug in the centre of
Naturally the combustion flame will reach the end gases in a small
combustion space more quickly than if the chamber were twice as wide. Additionally, a
central spark plug reduces flame travel to a minimum...