I have run both a uniflow and standard setup in a .40 size plane with muffler pressure. I didn't see any benefit to the uniflow, and I didn't like getting my muffler full of fuel every time I let off the throttle. If you think about it, the muffler pressure is much greater than any variance caused by the fuel level in the tank. The uniflow does do what is claimed, but in our systems it is so small a difference that it just doesn't matter. I am happier with a single clunk setup and won't use a uniflow again unless I decide to run a plane that doesn't use muffler pressure.