RK, that little DKW is awesome,that Yanmar is a good example of a state of the art Diesel engine at least the horse runs on unrefined grass. We love our infernal engines-but I dont know if my 140 HP Civic engine would move 2310 short tons a foot in a minute or not.I just feel that our rating system could be a little more meaningful .Seems to me like torque is the force that overcomes inertia and horsepower is the energy to do work or overcome resistance-Kevin
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.
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.
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
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.
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 
well, let me ask this,does say 100 hp take the same amount of gas basically,regardless of engine configuration?-Kevin
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.
Gives a much better explanation that I can and has some interesting numbers to consider.
Thank you MTraveler,that was really helpful-Does anybody know anything about the the so called adibatic engine? Kevin
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.
Hey, 100hp/L can be reliable. Look at the S2000 ;)
Honda:
When horse power per liter maters more than miles per hour 
kmccune, A hydraulic jack does not produce any force, It multiplies the force that you exert on the handle. You might move a jack handle through a 4 foot arc to lift the car an inch or two. That is simple leverage, swapping distance for force. Fluid is used as a transfer medium because it is incompressible. You can crank on a jack for a good part of a minute to lift the car a foot or so. 10 HP, on the other hand, could winch a 3300 lb. car 100 feet up a vertical shaft in a minute once it got going (not counting for losses). It would take some extra power to accelerate to that rate, though.
So the arm is the prime mover and the jack is like the transmission?-Kevin
All things being equal, which they seldom are, torque is equally important. But to me, horsepower and torque at what specific rpm is more so. When you throw the transmission into the mix, which IMO is equally important, you really can’t separate the power train. Yes, car makers do use similar motors in both their cars and trucks while lowering the hp ratings in the interest of longevity. But, reworking the transmission and final drive is equally if not more important. Don’t believe for one moment that any two motors with the same hp rating will have the same performance and can be interchanged. electric motors yes…gas motors no.
kmccune. Yes. The jack does act as a transmission. You arms pumping the handle supply the HP, and the jack converts it into an amount of force that can lift the car.
dagosa, You’re absolutely right. Torque is important. Without torque, there is no horsepower, and having a lot of torque available in the lower midrange (say, 2000-2500 RPM) gives you an amount of HP at that RPM that will move you along. A good example of this is the Honda S 2000 mentioned in this thread. When the car journalists tested it, it did 0-60 MPH in 5.5 seconds. The catch is, the engine doesn’t produce a whole lot of torque, so in order to get that time, they revved the engine to 7500 RPM and side stepped the clutch. If you drove your car like that, your driveline repair costs would exceed your car payments! The engine supplies the power, having transmission and final drive ratios that are well-suited to the engine and the weight of the car allows you to make effective use of that power.
In comparing cars of similar types – such as one sedan to another sedan – the HP of the engine is a spec worth looking at. It doesn’t really matter what the units are when you are doing a comparison of one car to another. As long as the units are the same one car to the other, the one with the higher HP number will have more power. HP is just one factor in how the car drives though. Weight cancels out HP to some extent for example.
If what you really want to know is how well the engine power is delivered to the driver, one of the best specs to look at is the car’s zero-60 mph acceleration time. The first VW Beetle had a 25 HP engine, and its 0-60 time was only slightly under 30 seconds. And that’s on a flat road on a calm day. If the wind was blowing toward you, it might never go 60 mph. Most modern econo-boxes, depending upon whether they are manual or auto transmission, are between 9-11 seconds. Most drivers find that adequate. The fastest cars – such as the Tesla roadster – are 3-5 seconds.
Very interesting,I do favor vehicles with a power to weight 17 to 1 or better and I agree the wrong gearing can make a vehicle a complete dog,yes back in the 50’s 12 second 0-60 was considered right peppy-if I had a choice between shaving 300 lbs off my vehicle or gaining 10 HP,I would take the weight reduction-Kevin PS-Thanks folks for the replies.
RE adiabetic, I found this reference to Smokey Yunick and his efforts at an adiabetic engine but I recall that he had a story on the development of such technology in the late 60s. At the time I thought it was a joke.
Thanks RK,but I know at one time the manus’were quite serious about the ceramic engines and what have you.I wonder if “Heanium” was an offshot of this research?
An article from Hot Rod 9-2010 about Yunick’s engine.
http://www.hotrod.com/techarticles/engine/hrdp_1009_what_ever_happened_to_smokeys_hot_vapor_engine/viewall.html
The Heany Industries web site.
http://www.wireworld.com/heany/