Going to make the expansion chamber smaller, so that it’s deeper underground, then funnel the gases through a maze made out of blocks filled with sand. There’s a big hole filled with builders sand that forms the center of this structure, with any luck the sand and the irregular direction of the baffled blocks and the fact that it’s all underground will make this super silent.
Perimeter foundations with sandy center:
And a maze of baffles including one at an odd angle to break the sound and try and reduce echoes. The gap between the blocks is always about three times the size of the surface area of the existing exhaust pipe, so shouldn’t have a problem with back-pressure on the engine.
After waiting for the cement to dry, I filled the holes up with sand, leaving a gap towards the top for the concrete to fill:
Used wooden blanks to form the roof and laid some mesh over it to add some strength to the croncrete
…and covered it all in concrete
