Fast planes
If you look at my Avatar, thats one of my Quarter 40 planes. It uses a Nelson .40 engine turning a prop at about 23,000 rpms generating close to 3 hp.
The picture John posted is a FAI plane, that runs on NO nitro. These planes also run on .40 sized engines, however they also use full length tuned pipes, and pretty much anything goes.
FAI is popular internationally, but there are virtual NO FAI races in the states other than the qualifiers for Team USA, and traveling to to the World Championships.