Boxer only, and IF both exhausts connected via T-connection to the tank only, you can leave out the craptrap, IF you are willing to replace the feltclunk about every year or so.
All other engines, I would not do so, but guys, a bit of ingenuity makes a craptrap a total non-issue: the one in this vid is 100% maintenance free (non aerobatic, though).

Just let your imagination run wild, that's how the best ideas are conceived (the worst ones too, but let's forget about those )