Proptop,
It was a differant engine and todays plugs may not be the same but I got more Revs on the K&B 4C plug over OS-F and Fox miracle plugs on high nitro (25%), but you had to lean it down from the hotter plugs becase the extra fuel was quenching the hot plug. Picked up another 300 RPM for a total of 600 RPM from 15% nitro.