.........and bladders can only supply enough consistent pressure on demand to a certain point, then you go full circle back to what the C/L SPEED guys use, which is either pressure off the pipe or off the crankcase. The problem with pipe pressure coming off 1/2A engines [with the clipped on muffler] is that it isn't a sealed system, so the pressure will be inconsistent. Back to the original post, with no pressure except for atmospheric, the engine is more sensitive to the models' pitch, attitude and G forces. A model engine with muffler pressure cares less which way the nose of the model is pointed.