MPG - What You Drive vs How You Drive It
Discussion
I've been thinking about this. Since getting 40mpg out of my E36 318is, and only achieving 37mpg out my old 316. Here we go:
If you have an engine capable of (for arguments sake) 200bhp, and an engine capable of 100bhp, it is reasonable to assume the car with 200bhp will have a noticeable difference in MPG. (Compare a 1.0 Clio to the 2.0 Renault Sport for instance, or E36 316 and E36 328)
But why? Surly if you only use 100bhp of the 200bhp and half the rev range (which is more than enough in most situations,) all this talk about getting a car that doesn't use as much petrol isn't really viable (to a point, you may take other variables into account such as drag, engine efficiency and weight).
Your thoughts?
If you have an engine capable of (for arguments sake) 200bhp, and an engine capable of 100bhp, it is reasonable to assume the car with 200bhp will have a noticeable difference in MPG. (Compare a 1.0 Clio to the 2.0 Renault Sport for instance, or E36 316 and E36 328)
But why? Surly if you only use 100bhp of the 200bhp and half the rev range (which is more than enough in most situations,) all this talk about getting a car that doesn't use as much petrol isn't really viable (to a point, you may take other variables into account such as drag, engine efficiency and weight).
Your thoughts?
A gross over-simplification: Internal combustion engines are at their most efficient when generating peak torque. So the closer you run the engine to peak torque the more efficient it will be at converting fuel into motive force. Peak torque is obviously generated at wide open throttle so you want an engine that runs as close to wide open throttle as possible for the speed you want to drive.
As long as you don't have to over-rev it to do so, an engine that you have to push hard to achieve what you want to do will be more efficient than one which does it easily.
As long as you don't have to over-rev it to do so, an engine that you have to push hard to achieve what you want to do will be more efficient than one which does it easily.
Edited by kambites on Monday 26th July 18:28
there is a difference between efficiency and economy.
as i understand it (very very simplified):
efficiency is how much of the fuels chemical energy is being turned into motive force, compared to how much is being wasted as heat, noise, etc.
economy is how much energy you use to get the same result. ie your small engine may well be no more efficient at burning fuel than your big engine, but as its burning less fuel overall it is more economical.
as i understand it (very very simplified):
efficiency is how much of the fuels chemical energy is being turned into motive force, compared to how much is being wasted as heat, noise, etc.
economy is how much energy you use to get the same result. ie your small engine may well be no more efficient at burning fuel than your big engine, but as its burning less fuel overall it is more economical.
Edited by deadtom on Monday 26th July 19:15
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