Yes what 1qwksport2.5r stated about combustion chamber shapes. But also the compression ratio changes. Low nitromethane glow fuel means you run a higher compression ratio. But higher nitromethane levels means you run a lower compression ratio.

But one thing to consider is the fuel consumption of a 2.10 glow engine. At full throttle it is quite thirsty. But with a tuned pipe that could double the amount of fuel it needs. So it could become quite spectacular for the amount of fuel needed to fly full throttle for 8 to 10 minutes.