Does anyone care to elaborate?

MTraveler · May 2012

Sorry kmccune you still have the definitions muddled. If you push on a wall and it doesn't move that's force. If you push on a wall and it does move that's work. Force times distance. How fast the wall moves is power. Force times distance/ time. Switching from HP to KW won't help. Underneath the principal is the same only the units are changed to confuse the remaining countries that haven't adopted SI

One of my personal favorite engines:
The Suzuki RP68 road racer.
3 cylinder 50cc rotary valve 2 stroke
19 hp @ 20,000 rpm
14 speed gear box.

Rod Knox · May 2012

It seems to me that the manufacturers are marketing horsepower numbers that are only momentarily produced. The Yanmar and the 300 horsepower Cummins engines are built to deliver their rated power continuously until they are worn out and that might easily be in excess of 10,000 hours. The DKW and the exotic automobile engines that produce 100 horsepower per liter can only produce that power in short bursts just prior to shifting to the next gear. That's can make for a great deal of fun but for reliable transportation such technology is somewhat of a hindrance.

kmccune · May 2012

Gee thanks guys(I do know that a hydraulic jack can produce a lot of force .but scarcely any power-a starter motor is a torque monster with scarcely any horsepower) probaly its just me,but it seems that some of these descriptions are a bit gray-Kevin

Rod Knox · May 2012

Isn't horsepower just part of the image. And image sells cars. The ad men make a great deal of color out of gray data. Mostly green.

shadowfax · May 2012

That's can make for a great deal of fun but for reliable transportation such technology is somewhat of a hindrance.

Hey, 100hp/L can be reliable. Look at the S2000 ;)

kmccune · May 2012

well, let me ask this,does say 100 hp take the same amount of gas basically,regardless of engine configuration?-Kevin

MTraveler · May 2012

The simple answer to your question is definitely not.
Starting at the beginning, if you put 1 liter of ideal fuel air mixture at atmospheric pressure in a sealed container and ignite it, the heat released by combustion will raise the temperature and pressure inside the container. Measure the heat released until the pressure inside the container returns to atmospheric and you will have the theoretical maximum amount of energy that can be converted to work. In the old days this was done in a thing called for obvious reason a bomb calorimeter. No mechanical device does a very good job of converting all of the heat to work.

Starting the same volume of fuel air mixture, add some energy to compress it, the more the better. Ignite the mixture, remembering it is the same amount of air and fuel and allow the mixture to do work against a piston. Up to a point the greater the distance the piston travels the more work can be captured from the expanding gasses. Connect the piston to a crankshaft and you have converted chemical energy to rotary motion.

For a given displacement and compression ratio, without supercharging there is a theoretical maximum amount of torque an engine can produce. A 1000cc engine can burn at most 1000cc of fuel air mixture per power stroke. Once you have reached that limit the only way to increase the power available is to increase the displacement or increase the rpms. If you are designing to a displacement limit increasing the rpms is the only option.

The unit you are looking for to compare the efficiency of engines is brake specific fuel consumption.

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

Gives a much better explanation that I can and has some interesting numbers to consider.

kmccune · May 2012

Thank you MTraveler,that was really helpful-Does anybody know anything about the the so called adibatic engine? Kevin

doubleclutch · May 2012

Horsepower is a very real concept, but it is one that most people have absolutely no understanding of when they talk about their "300 HP" cars. Think about this scenario. A hypothetical car will go 25 mph at 2000 RPM in a certain gear. In a lower gear, it will go 25 MPH at 4000 RPM. Well, you think, the engine, because of the torque multiplication of the shorter gear, should supply twice the thrust in the shorter gear, where it is running at 4000 RPM. This, however, is the case only if the engine produces the same amount of torque at 4000 RPM. If the engine is a wheezy thing with a single barrel carburetor that can't produce much torque above 3000 RPM, shifting to the lower gear will not do any good. This is why modern car engines have all them extra cams and valves, so they can run the needle off the tach while producing very near their maximum torque. Most cars will accelerate very quickly in first gear. If the engine produces near maximum torque all the way to redline, you can maintain this acceleration in first to 35-40 MPH instead of crapping out at 15 MPH.

A Z-06 Corvette engine that can make 505 HP at 6300 RPM is great for making a 3200 lb. car go fast. At 2500 RPM, it may only make about 200 or 225 HP, but 200 easily accessible HP will shove a car along awful fast. A Cat C-15 in an OTR tractor-trailor might also make 500 HP, but that HP comes at around 1800 RPM, and a greater portion of it is available throughout the usable rev range, so it is better suited to dragging 80,000 lbs. all over the country 11 hours a day. Besides, a Cat C-15 engine weighs as much as a Corvette, so it wouldn't really fit in the car.

bscar2 · May 2012

Hey, 100hp/L can be reliable. Look at the S2000 ;)

Honda:
When horse power per liter maters more than miles per hour :P

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