Hi Charley,
A few details that matter in all this ;
Methanol's energy 22Mj/Kg but requires 6.5Kg Air per 1Kg Methanol for combustion.
Nitromethane's energy is only 11Mj/Kg ,thats half that of methanol but only requires 1.7Kg Air per Kg Nitro.
Combustion in an IC engine has the amount of air fixed by the stroke/bore.
So for 1Kg of Air Methanol gives 22/6.5 =3.4 Kj and Nitro gives 11/1.7 =6.5 Kj ,thats nearly double that of Methanol = 100% increase.
Therefore a good rule of thumb is 10% Nitro = 10% more power etc.
Nitro also has a very high vaporization temp and so cools the engine more than methanol as it vaporises.

Brian