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It takes fewer moles of oxygen to burn a mole of methanol. Considering this, when O2 is the limiting factor, you will be able to burn more products and thus make more cylinder pressure. In this regard, methanol will make more power than ethanol.
Further, on a per mole basis, methanol produces less heat than ethanol. In this aspect, it burns cooler. Interestingly, many people who have logged their IAT's with water-methanol or ethanol injection have shown lower IAT's with ethanol. Why is this?
Methanol has a lower molar mass than ethanol. When we mix either substance with water, this is why we should be mixing by weight and not volume. Keeping this in mind, when the amount of water is our limiting factor, we will be able to use more moles of methanol. So while methanol may actually burn cooler on a per mole basis, we are now burning more moles than we would be doing with ethanol. This creates higher cylinder pressures, equating to more power.
This discussion is more relevant if we are burning either straight methanol or ethanol. In such a case, the amount of air will be a limiting factor and affect our power. Since we are using a 50/50 mixture, and only as an additive and not a standalone fuel source, the discrepancies between the two will be very slight. Even so, with water as our limiting agent, methanol will produce more power than ethanol (in this case the difference will be small).
I did mistakenly say that denatured alchohol was "100%" ethanol. It is ethanol, but like 1speedbike said, it is unreasonable to say that it is 100%. I meant this more as a means of saying that the primary constituent is ethanol, but I certainly could have worded this better.
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