<quote name="Alex Esplin" date="Wed, 11 Jun 2008 at 22:03 -0600"> > On Wed, Jun 11, 2008 at 9:46 PM, Von Fugal <[EMAIL PROTECTED]> wrote: > > Just a note, turbo chargers and superchargers do NOT increase > > efficiency, only power. *charged vehicles generally get lower mpg. > > Not true. Power and efficiency are the same thing in a different > context. When you have a charger making a bunch of boost and the > pedal is all the way to the floor you are definitely making more power > than if the same engine was naturally aspirated (NA). In this case > the fact that you are getting more boom for the same amount of gas is > academic because you're basically pouring gas out on the ground. The > reason charged vehicles get lower mpg is _not_ because they are less > efficient. It's because the people who drive them have heavy feet.
I'll buy that power and efficiency are _related_. But they are not the same thing. Your bigger muscles can lift 50 lb easier, they have more power. But they use more energy than small muscles. Efficiency is power produced / energy used. Power is simply power, it doesn't care how much energy it used. If you increase power _without_ increasing energy (fuel consumption) then by definitino you increase efficiency. > More air means bigger boom. I'm sure we all agree on that by now. > Bigger boom means less gas for the same amount of power. So when your > foot is not all the way to the floor you do indeed get better > efficiency and therefore mileage. More power == more efficient if > you're not pouring gas out on the ground. If you add more air and get better compression that indeed can make a bigger boom. But you also have to maintain the proper fuel/air ratio. More air == bigger boom, but that doesn't necessarily mean the same amount of fuel was used. You might use more fuel, you might use less, you might use more, but at a lesser rate to which you get more power, that would translate to more efficiency. But bigger boom != more efficiency. > My Honda Fit, which gets better mileage on the freeway than my old > Civic did, gets significantly worse mileage around town. Why? > Because it has less power. Less power == more effort to do the same > amount of work. Stick anything on my car to increase it's power and > my in-town mileage will go up (to a point) because it takes less > effort to do the work. Freeway vs town mileage has several factors. Among which are stop/go and power band. Drive your car 70 mph and note your rpms, then drive your car again with the same rpms but in a lower gear, without stopping and starting, and see if you get the same mileage (or slightly better due to less air drag). > It takes less effort for me to lift 50 pounds than it takes my wife. > Because my muscles are larger and generate more power than hers, that > same 50 pounds is less of an obstacle and I can lift it and put it > back down many more times than she can. I'm sure I could come up with > more examples, but I hope we're all getting the point. > > I spent a good portion of my younger days as a mechanic, both in the > Army and the civilian world and believe me, I have played around with > _lots_ of engines. There is a reason that nearly all military diesel > engines have a turbo attached to them, and that reason is not solely > for max power. Our ambulance HMMVs (had turbos) when I was in the > Army had a larger "effective range" than the NA HMMVs did. One last > time, more power == more efficiency. I'll concede that *charging can increase efficiency, but it's not a direct correlation with the increased power. Von Fugal
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