[donsor]

I vaguely remembered from my previous Physics class the "Input Equals Output" which amounted to 100% efficiency. But the 100% effici3ncy is not always achievable so the Output could be somewhat less. Does this theory or accepted fact still hold true in today's advanced technology? For example: My 2000 Acura 3.2 TL is advertised to have 21MPG City fuel efficiency. Today Acura is boasting a mileage of around 30MPG. How do car manufacturers achieve such fuel efficiency? I suspect that something else in the automobile such as weight or performance and Return On Investment had to be considered. What say you?

[ma0641]

There are loads of changes in 14 years. The fuel distribution technology in your 2000 is vastly different than today, which is direct injection, like a diesel. Is the engine displacement the same? Your 2000 probably has a 4 speed, my 2006 Nissan has a six speed and at 70MPH is only turning 2000 RPM. I had a 1957 TR3 with a 4 speed that at 70 was turning 3500 RPM. Some newer models have 10 speed. Ford is going to Aluminum body panels to reduce weight. Aerodynamics plays a part. I would say weight, fuel injection and RPM are the 3 big factors. Even with all those changes, the efficiency of a gas engine is probably less than 20-25%.

[ebaines]

Does this theory or accepted fact still hold true in today's advanced technology?

Indeed it is still true - the idea that output could be greater than input violates the 2nd law of thermodynamcs, and would allow the development of a perpetual motion machine.

In addition to the technologies that ma0641 mentioned I would add that modern electronic engine management systems and sensors are much more sophisticated now, having the ability to change and optimize the ignition timing and air/fuel mixture constantly depending on variables such as air temp, exhaust mixture, engine load, and RPM.