Dave,


The torque and power curves of an engine are by far more dependent on the timing numbers, than on the nitro content of the fuel. In timing numbers I include intake bypass(es), exhaust port(s), shaft valve port and compression ratio.

In an engine with given timing numbers... Well, let us look at it this way:

With more nitro, the mass, the density and the viscosity of the intake charge are larger, since more fuel is needed for a given amount of air.
Also, these qualities are also true of the exhaust gasses.

These would both tend to make the engine breath more efficiently at slightly lower RPM levels, thus lowering the RPM, at which peak HP and peak torque appear.

In the case of four-stroke engines, the lower compression ratio needed for higher nitro, decreases the induction efficiency, since vacuum builds up more slowly, as the piston descends. This would also lower the peak HP and Peak torque RPM levels.
This has little effect, if any in a two-stroke engine, since there is no actual induction (sub-piston pressure pushes the fresh mixture into the cylinder).

All these effects are minor at most...