The measuring chamber (1) is arranged between an engine side and an outlet connection flange. The engine side endface (3) of the measuring chamber has a circular slot, which stands in flow communication with at least one cool air bore, pointing to the outside, and at least one duct for supplying cooling air to the measuring chamber opening out in to the measuring chamber. The measuring chamber is designed cylindrically and is provided with an annular slot on its endface facing the engine, which has radial cooling air bore pointing to the outside, also with ducts arranged over the periphery of the slot, standing in flow communication, running obliquely radially inwards, opening out in to the measuring chamber. An expansion compensation piece (21) can be positioned longitudinally in the test bed.
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