Tuners of vintage Porsches, tuners of vintage VWs, tuners of Harley-Davidsons, pretty much tuners of any air cooled big bore engine being it vintage or modern-ish vintage likes to convert to dual plug heads for better flame propagation, especially in hemispherical combustion chambers. The result is not so much a horsepower increase, but a torque and throttle response increase instead, due to better combustion allowing a point higher in compression ratio and cooler running temps. But I vaguely remember reading something about someone saying all the trouble to tap for that second plug and then figure out the correct retarded timing was unnecessary if etchings called "flame channels" or something similar were shallowly carved into the surface of the combustion chamber. If I remember correctly, these etched lines went from the spark plug opening to the other side of the chamber where a second plug would theoretically be tapped; their purpose was to somehow speed the spark flame along the chamber so that no second plug was needed. Anybody know what I'm vaguely remembering, or is my subconscious playing tricks on me?