I'll add a few factoids that I have had experience with...

Closest clearance (piston to head) on a .12 engine is .4mm
Maximum effective clearance for .12 engine is .8mm

Closest clearance for .21-.32 engine .5-.55mm
Maximum effective clearance for .21-.32 engine 1.1-1.3mm

Lowering head clearance WILL raise combustion pressure and combustion temperature respectively. (Thermal efficiency may go up but negligibly)

Raising Nitro % will also have similar effect (more pressure and more heat)

Raising Nitro % requires more alcohol to keep similar burn ratios (this explains why we need to set carb richer when changine to more nitro) (Also this explains why miliage suffers when going to higher nitro)

Raising ex port will cause higher rpm effective tq peak

Widening ex port will have similar effect without losses on midrange

Water vapor DOES NOT convert itself to hydrogen and oxygen in the combustion process. (A. if it did there would be little use for fuel cell engines) (B. the combustion temp. is far too low in our engines for this to even begin to take place) (C. Water vapor in internal combustion engines only turns to steam during combustion)

The Combustion temps of our engines are much lower than that of gasoline or petrol engines. (Ex temps of gasoline engines in the 1200 deg range and Glow engines in the 400-500 deg range)

Hotter air = leaner Colder air = richer

More humidity = leaner Less humidity = richer (this is due to water vapor displacing useable fuel molecules in the intake charge requiring less fuel due to less oxygen)

BK