Stadler Rail refers to this centrally positioned motorised carriage as

a 'power pack'. On either side is a Deutz V8 sixteen litre diesel engine with a corridor down the centre that certainly gets hot when the engines are running but is surprisingly quiet! The engines provide power for the train and all its support systems and certainly seem to do a good job with it having rapid acceleration. Due to the engines located in this position, the floors of the carriages are able to be lower than normal very similar to many continental trains giving the train a distinct air of roominess. Power pack 971410 is part of set 755410 seen at Sheringham station that will soon work a Norwich service.