Recently I helped replaced the stock pipe on air frame with a tams pipe on a 180 sized jet (I think it may be a skymaster dragon? or feibao?) for and took out the stock Chinese pipe . The Tams pipe certainly was higher quality but the thing to notice was that the tam pipe was 10m smaller in diameter. After flying it was clear that the jet gained some speed I would say 10-15% faster. It was also clear takes off took more runway (less thrust?).

This has me thinking, do smaller diameter pipes increase air frame speed? I suppose Its similar to a garden hose, decreasing diameter increases pressure and speed of the water. I'm assuming its raises temperature inside the pipe so the pipe would need to be of high quality to be able to handle the extra temperature.

On some of the skymaster jets are not coming with 300N options, in these the the 300N has larger diameter? is this to slow the turbine down vs a 200N which has a smaller diameter pipe. What if using he 200N pipe on a 300N turbine would that increase speed of the 300N?