No, "weight" is not a unit of anything. Pounds are units of mass. Slugs are units of mass.
You are one confused fool, failing to understand the simple fact that "weight" is an ambiguous word, one with several different meanings.
The word "weight" entered Old English over 1000 years ago, meaning the quantity measured with a balance. That quantity is mass, not force. It was used as a measure of how much stuff people had, for the purpose of trade. We still use the very same word today, with the very same meaning, for the very same purposes.
Weight is never a force when anybody talks about "net weight" of anything, nor about "tare weight" of its container. Naturally, when products in American supermarkets and auto parts stores and whatever include pounds and ounces for this weight, they are every bit as much units of mass as the grams and kilograms which appear right alongside them on the same label. In fact, we no longer have independent standards for those pounds; since a 1959 international agreement, the common, worldwide definition of these pounds is as units of mass exactly equal to 0.45359237 kg.
Weight is never a force when anybody talks about "troy weight" of anything. That's one way the troy units differ not only from their avoirdupois cousins, but from grams and kilograms as well--they have never spawned units of force of the same name. There is no troy ounce force, never has been.
Weight is never a force when anybody talks about "carat weight" of anything (5 carats = 1 gram in the modern definition).
Curb weight is 2,733 pounds--about 250 pounds heavier than a Corolla, and 330 pounds more then a Ford Focus sedan.
Now, Rod, it is your turn. Like you said, those kilograms are units of mass. Now, why in the hell don't you just explain to us all exactly what is done differently when this "curb weight" is measured in pounds, from what is done when it is measured in kilograms.
While you are at it, tell us why in the world the manufacturers would measure two different quantities for this purpose in the first place?
Or just wake up and smell the coffee. Let's add another to my list above: weight is never a force when anybody talks about "curb weight" or "kerb weight." It doesn't make any difference how they spell it. It doesn't make any difference whatsoever what units they use to express it. Nobody in the whole wide world ever measures curb weight in newtons, and nobody in the whole wide world ever measures curb weight in pounds force.
You can. But the only units of energy in the only subsystem which includes slugs are foot-pounds force.
You don't have pounds force. You have pounds mass.
If you use pounds mass and feet per second in your kinetic energy formula, the result is in foot poundals. It is just as easy to convert foot poundals to Btu, as your calculations converting foot pounds force to Btu were.
If the curb weight is indeed 1311 kg, as listed in one of the sites above, at exactly what areas on the surface of the earth would that much mass exert a force of 2890 pounds force, measured to the nearest pound force? Note that even if you limit yourself to sea level on the surface of the earth, a mass of 1311 +/0.5 kg will exert a force of from 2881.4 lbf to 2898.9 lbf (throw in elevation, including Mt. Chimborazo, the highest mountain on earth in both ways relevant to this discussion, and the variation on the surface of the earth is even greater). But 1311 kg is 2890 lb anywhere on earth, or anywhere else.
If curb weight were in pounds force, as you erroneously believed, you'd never have more than 2 significant digits, if all you know about location is that it is somewhere on earth.
It is indeed relevant to figuring any change in the fuel efficiency overall.
I'm intrigued by the idea, but I've never even seen a Prius.
Gene Nygaard