thats awesome!
about six years ago i built a potato gun that was fueled by acetylene that was pressurized injected.
we have no clue how far the potato went, but each time we shot the gun we propped it up to a '91 chev s10 p/u and it would move the front tires about 8" to 14"
we had to replace the steel combustion chamber after two shots, but it was fun.