(23 Mar 2014, 5:56 am)G-CPTN wrote From:-
It's quite easy to see that the larger capacity engines offer higher torques (and, therefore, better 'pulling power'). Higher horsepower will result at the same engine revolutions (power is torque times revolutions).

Two different approaches to the same topic:-

http://www.largiader.com/articles/torque.html

http://www.epi-eng.com/piston_engine_tec...torque.htm

An engine with higher torque is capable of pulling longer gearing ratios, thereby giving the same roadspeed at lower engine revolutions.

The work done is the same (for equivalent roadspeed) but consumption will depend on the comparative economy of the engines at those revolutions.
The smaller capacity engine at higher engine revolutions might well be using more fuel to achieve this - but this will depend on the engine management system.
It is, perhaps, obvious that the components within the smaller capacity engine will 'run further' to achieve the same performance, and, therefore be expected to wear out sooner.

Conversely, if the gearing ratios are the same the larger capacity engine will probably use more fuel (again, depending on the engine management system). Throttle opening position will determine how much fuel is delivered (and how much performance is delivered) so judicious use of the pedal will reduce fuel consumption. A sophisticated 'drive by wire' control could optimise this.

240 bhp is quite frankly shocking.
http://www.motortorque.com/guides/buying...dget-17630 - There are some cars with even more bhp than the bus engine! Time for a fleet of taxibuses?

Seriously though, the mid range 8 litre engine, isn't too much different to the current lumps in the B9's.

If the correct bus, is allocated to the correct route - such as a town and city bus as you suggest - in theory, there shouldn't be too many issues.
Stick a 5 litre on a long run and you are asking for problems, no matter how 'economical' or fuel efficient the engine is.