I got an answer on the poppet valve exhaust. There should never be positive pressure build up inside a flame eater engine. The Poppin gets away without an exhaust stack because if the piston moving towards top dead center causes any positive pressure, the .002" thick valve flexes enough to release this pressure. On larger flame eaters where the sliding valve is mechanically driven and does not flex, you need the exhaust valve which is indeed a poppet valve to release this pressure. This type of valve is basically a small ball setting in a cone. It will let pressure out, but seals automatically when the piston is creating suction to pull the flame into the engine. Some engines have a stack, although it is just for show. Other engines just have the exposed valve setting on top of the cylinder at the end opposite to the crankshaft.
