Quote:
Originally Posted by jakobnev
I'd say Eco is about proportional to the inverse of the cubic root of power.
(A car of the same era and size can have eight times the power and only have twice the fuel consumption)
|
I think in practice it is more plain inversely proportional however, due to behaviors like over-accelerating (and related over-braking) and lots of idling and long warm ups and aggressive use of extra horsepower. You have to account for the typical driver and mentality for a certain type of machine.
Besides there are more examples of like a 60hp metro getting 3 times the mpg of a 160 hp american car. And said metro will not get 70+mpg if you operate it at 60hp. So I think it is a reasonably valid equation myself. eco=1/hp.
Also a larger displacement engine will have larger pumping losses when the throttle is partially closed (which it will be most of the time-moreso than a smaller engine with more load), and it typically weighs more. And Turbos are not good for BSFC on gas engines typically.
There's plenty of yahoos who *wish* they can have their cake and eat it too, but there are practical limitations in the way.