Wolfy- You repeated what I was getting at, just in different terms. If a Mack truck only weighed 2500#, (Or the Corolla engine had to pull the weight of the Mack truck), the Mack would use WAY less fuel. I get 21mpg in my 6000# 1stGen. If a truck weighing in at 60K gets 7mpg, it is far more efficient on a per pound basis than my pickup.
My response was to the poster who commented on his new truck getting worse MPG than his 96, but it had twice the power, so he seemed to me to be excusing it. If you are moving 2 similar sized rigs, the one getting 12MPG isnt using any (appreciably) more power than the one getting 23. It still only takes x- hp to move down the road empty, whether you have 180 or 1800hp available.
Paul Barker- the "work" here is moving the entire assembly down the road- truck, driver, etc, not just the driver. See my comparison of the truck and the pickup. 10x the weight, but only 3x the fuel used. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------dpucket , you or no one else is going to have power available and not use it . you act like that if two trucks are pulling the same load then only the horsepower needed to pull it is all that is going to be used . torque is the power of the engine and horsepower is the speed in which the engine can apply the tourque . if you are starting at a red light or pulling a load there is no one alive that will just ease around and make sure that you don't use the extra hp . if you use the extra hp you will use more energy . i would like to see you take a 180 hp and a 1800 hp engine and put them side by side and just idle them and use the same amount of fuel . you can't do it . you need to take a dose of reality and get into the real world . what you say sounds good on paper , but doesn't work in real life . you must be an engineer . i have to deal with them every day on the job and they are always coming up with big ideas on paper that just don't work in real life .