all engine at same capacity nearly share the same fuel consumption, engine f/c on can be judge base on many factors
-head design
valve size,valve angle,port flow,port size
-cam design
duration,lifting,advance retard profiling function
-block design
bore,stroke
-engine design
material used etc - iron, alloy
weight of the material
but still the f/c roughly run the same...
the main reason for high f/c basically is the gearbox...
it can determine how hard core your fuel can go with simple calculation on gear ratio..
for example....
sample 1
you work in the city, you dont travel outstation that often...
you running 4.3 final drive...
that should be good combo...
but if you running 3.6 final drive in city driving...
you can determine ur fuel consumption will be mad hell kills ur pocket...
try those even lower final drive..
sample 2
you always travel to penang, then back to kl, then to jb, sg
then back to kl again to penang kedah
you running 4.7 final drive...
lets see how your car f/c feels like...
so... dont think too much on the engine itself..
if you think like that... you better of think of the chassis.. and start throwing all your car seat and acc, see how much you can save on weight...
hahahaha....