O.K., then you'll need more static compression ratio. I would resist the temptation to do it with domed pistons though. The dome gets in the way of the flame kernel as it is travelling across the chamber. Do it with flat-tops and a smaller chamber.

The motor you were describing ran good because you had optimized the DYNAMIC compression ratio with high static compression ratio and a relatively short cam with an early intake closing point.

I think the only way you're going to be able to do what you want to is with 64 cc chambers or use the 56 cc heads with a dished piston. With 64 cc heads and flat-tops, you'd be at 10.44:1 and could run pump gas with the tight 0.040" squish and a cam such as this.....(112 LSA)
http://www.cranecams.com/?show=brows...tType=camshaft