Fuel & Diesel? Are they lugging around a whole tank of Diesel for fun? :P
Joking aside, the powerpack as fitted to the 80x (12V 1600 R80L) weighs in at 6.75t wet* but it is not clear if that includes the generator. Add in the 2.5t of fuel(s), and call it 10t (including the radiators, fans, etc) additional per diesel engine. Run the maths through and a pure EMU 801 (803?) comes in at very handy average 1.67ton/m (for reference an individual mk3 comes in at 1.43). Even with the IEP last mile engine fitted a 5 car 801 comes in at 1.75ton/m
*presuming that the high power one is the heaviest - not an unfair assumption
I stand corrected. The MR article (May) uses 7.4t per pack for the Class 800 including the fuel (1.3t). I make that 1.73t / m (247-22.2 / 130) if the weight of diesel traction were avoided.
However this doesn't change a great deal. 22.2t from 247t is still <10% and as shown the Class 800 Bi-Mode is still significantly lighter per metre than the Class 390, as well as the 7.4t being equivalent to roughly the seated passenger weight of the powered vehicle when full. None of this will touch the sides of a £1bn business case between Kettering and Sheffield, as evidenced by the lack of one, and subsequent cancellation.
Of course, were there a 5-10min time saving as well, which might have been true 50 years ago, the a lot of value of time and revenue aspects would come into play. But the Bi-Modes, as well as the more obvious example of Class 221 on the WCML and ECML show this isn't really the case.