Quote:
Originally Posted by NoD~
Lets say you have a 1.0L engine VS a 2.0L engine. They both use the same technologies, such as fuel injection, cam specs, etc. Lets assume for this comparison that they weigh the same. Efficiency is just about even on these engines.
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What do you mean by "efficiency is just about even"? There are lots of different ways to measure or state efficiency...
A smaller-displacement engine will either have fewer cylinders, or will have smaller cylinders and/or shorter stroke. Those all change the efficiency and power-delivery characteristics of an engine. (Long-stroke motors tend to make more torque, short-stroke ones can rev more easily, for instance. And fewer larger cylinders tend to have less friction than a larger number of smaller ones.)
You can mess with all sorts of things to get similar fuel consumption numbers out of your 1.0 liter and 2.0 liter engines for some circumstances. But I don't think you can match the full BSFC curves.
If you do match consumption figures and/or BSFC, you've still got a different amount of maximum power available to you from those different-displacement motors. So 80% load on the larger one will be making more power than 80% load on the smaller one.
It gets complex pretty quickly...
Now, if you somehow matched fuel consumption on each engine completely, you'd have the same fuel consumption in each case. But that's a tautology--assume X to start, and you end with X.
In the real world, a smaller engine should still get better MPG than a larger one. Even doing P&G--but the pulses that the car with the smaller engine makes will be slower.
-soD