 The Armstrong Siddeley Mamba turboprop was then chosen as the basis for the N-20's engines, with the propeller reduction gear replaced by a low pressure compressor.This powerplant was named Swiss Mamba SM-1, the conversion was carried out in 1948 by EFW, with only six engines built (four fitted to the N-20 with two spares).One of the spare engines is today part of the Swiss Museum of Transport, at the Flieger-Flab-Museum Dübendorf.