Turboshaft

Half-baked.

A tin can turbo shaft. I've seen some tin can jet builds. I'd like to do that with a turboshaft. I like the designs where the compressed air is used to cool the combustion chamber, which also pre-heats the air.

Output to a belt system. One component would be a motor/alternator. This could be used as the starter motor, but once the system was self-sustaining, it could be used as an alternator. This gives us an electrical source to run a fuel pump.

One idea I'd like to look at a bit more is using thermal expansion to my advantage. The seals around the hot components could be made of different metals with different thermal expansion so that they seal tighter at higher temperatures.