AMB, does this Irvine .15 you have got a blue head? I had one of their first versions they made for freeflight. This engine was clocked at 39,000 RPM with a 7 inch prop on FAI fuel. Although it did have a glow button for a combustion insert, which I later exchanged for a more convenient one that I manufactured, machined to accept a turbo style plug. The glow buttons became hard to get.