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Originally Posted by Dean
So what was your point if that was not it, and what evidence do you have for significant increases in gas millage since the introductions I referenced?
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My point is that your assertion that a smaller engine is more fuel efficient is not necessarily correct. AFRs have nothing to do with it. A larger engine which is running at very light loads (and no 4 cylinder on the market could really be called "large") is as efficient as a smaller one being asked to make the same amount of torque at a given time. The efficiency of the engine has to do with how well it turns each mole of fuel into heat, and then how efficiently it converts that heat into mechanical force. In a general sense, smaller engines are more efficient only because they
can't burn more fuel to make more power like a larger engine can, thus using more fuel to travel a given distance.
The proof that engines are getting more efficent is in the hp/displacement ratios AND the EPA estimates. Dean, think back to cars you have previously owned. Categorize them by rough displacement, typical fuel economy, and power. Any way you want to compare them, I guarantee that your A4 and porobably your WRX compare favorbaly in terms of power:fuel economy, economy:displacement, and power:displacement. I previously owned a 2.4 liter toyota Celica, and a 2.8 liter Nissan 280ZX. My RS trounces each of them in both power and fuel economy (although it's close on power with the Z) and is heavier than each one to boot. The were both EFI and distributor-based ignition.
You argue that the Justy motor gets better fuel economy because it is small. Unfortunately, you ignore the other factors that go into its economy- the extreme lightweight, small frontal area, and lack of
capacity to make enough power just to get out of its own way. I stand beside my assertion that the 2.5 liter non-turbo motor in the 2006/7 Subarus would get equal or better fuel economy compared to the Justy motor if you were to put it in a Justy, and drive at speeds close to what the Justy is capable of because it is more efficient at turning chemical energy into torque.
Back once again from the land of theory to the application at hand, which is Jeremiah's dad's new car, I argue that if he is looking to save money through fuel economy, that is simply not possible given the vehicle he is replacing. As such, other factors like build quality, power, personal preference etc. are going to outweigh maximum possible fuel economy. We're just trying to help suggest cars with decent economy that fit his other stated or assumed needs- AWD, not a beater piece of crap, equal or greater build quality to his forester, and inexpensive to own.