Glow engines are more powerful. To be precise an engine running on a methanol + nitromethane fuel will give more power than the same engine converted to spark ignition and running on gas [ petrol ]

Petrol 737.22 Kg / m3

Methanol 791.30 Kg / m3

So methanol weighs a little more than petrol but that is only part of the story as an engine running on methanol uses a lot more fuel than the same engine running on petrol so you need a bigger tank.