@kmccune "a truer rating of an engines output in my estimation is kw,"
Why? The KW is only the metric version of HP. There is a very common misconception that the KW is an electrical unit because we use it to measure electrical power in the US but we could just as easily measure electrical power in horsepower.
Drawbar power formula:
If your truck is pulling with a force of 550 pounds at the drawbar while going 1 foot per second, it is delivering one horsepower to the trailer. Drawbar horsepower = pounds of force X feet per second / 550
If your truck is pulling with a force of 1000 Newtons while going one meter per second, it is delivering one KW of power to the trailer hitch.
Drawbar KW = force in Newtons X speed in meters per second / 1000
You might notice that I made no mention of volts and amps. There is a common misconception that the watt is defined as one volt times one amp. Actually the definition is backwards. It’s the volt that is defined by the watt, not vice versa. The watt has a definition completely independent of electrical units.
I would bet that under the same conditions these new high power pickup trucks would get better mileage than the 1950 1 ton Chevrolet pickup I once owned with its Stovebolt 6 engine. No truck today, however could compare in ride quality with that old Chevy. School bus seats had more padding. We pickup drivers weren’t wimps in the old days.
Because I think in metrics, KW makes an heck of a lot more sense to me then some abstract HP figure,I can usually figure out the capacity of an engine by the KW rating and I look on the KW rating as an honest evaluation of the work an engine can perform,The official measuring system of the US is metric(since 1889) why dont we use it?My mind handles decimals a lot better then fractions.
Everything is relative to the times you are in. Today, , you are competing with faster and more dense traffic. Heavier, more powerful tow vehicles are safer. You don’t think so ? Tackle a highway of semis driving a 55 hp Beetle. That’s essentially what towing with these underpowered rigs would give you. Not only are today’s more powerful vehicles safer because they give you more options, but they handle better and the coordination of braking between the two is invaluable to maintaining control and stopping. Of course, there is nothing you can say to some who prefer the days of old who actually survived them. It’s easier to convince those who did not.
“I’ve been out of the camping scene for a while” …and times have changed.
While some of us recognize and appreciate the technological advances of todays automobiles and trucks, @dagosa, we still find it somewhat commical to see the hyperbole of advertising claims. There is little chance that an owner of a highly touted 300+ hp Nissan sedan would ever drive in a situation that would come anywhere near that potential. Large diesel trucks, on the other hand, take full advantage of innovations and as I pass trucks on the highway and hear their engine somewhat effortlessly cruising along with 90,000 lbs of gross weight while exceeding 6 mpg. Forty years ago a Cummins powered Freightliner grossing 70,000 gross would have struggled along screaming to keep above 70 mph with the bias ply tires crying loud enough to be heard a mile away and 4 mpg was all that might be expected. Not to mention it is very rare these days to see black smoke belching from a diesel.
The unit known as the horsepower was based on how much work a horse could do in a working day pumping water out of mines, not how much power it could generate during a short sprint.
A human can generate one horsepower for a few seconds.
James Watt standardized it at 33000 ft-lb per minute to measure the power output of his steam engines which were first used to pump water out of mines. The owners of mines were familiar with how much water a typical horse could haul out of a mine in one day and needed to know what size engine was needed to replace the horses they used to use.
Just for fun, let’s consider how much power it takes to accelerate a 1100 pound race horse from zero to its 40 mph gallop speed in 5 seconds.
At 40 mph, a 1100 pound horse has 58,788 ft-lb of kinetic energy. In order to gain that energy in five seconds, it had to generate 11,758 ft-lb of energy per second. 11,788 ft-lb per second/550 ft-lb per horsepower-second = 21.4 horsepower.
I’m not sure how many seconds it takes for these horses to reach their top speed, it may be even less than five seconds, in which case, they can generate even more horsepower in a burst.
The best example of onboard electric generation’s terrific pulling power is a diesel locomotive. There is no direct connection between the diesel and drive wheels. It is driven by electric motors.
I just think KW is more honest because it works for me,it gives me an idea of what the engine is truly capable of,didnt know a human could generate a HP(thought champion cyclists could do maybe 0.4) anyway a sq meter of good PV array will generate on the order of 750 watts(or convert sunlight to electricity)on a bright day,wow,close to a HP(can get my teeth in that one!)suddenly the future is a bit brighter.
If a 100 pound man can scramble up a 5.5 ft vertical stairway in one second, his legs were generating one horsepower.
The sustained power of a healthy human is somewhere on the order of 1/8 horsepower or so I hear. Champion athletes likely can do much more.
Electric motors differ from internal combustion engines in that an engine’s rating is usually the very maximum the engine can deliver.
Electric motors are more like horses, the horsepower rating is more like a continuous duty redline than the max it can deliver. What determines an electric motors continuous duty rating is overheating. That rating has to be derated at high altitudes or high ambient temperatures because of the lessened cooling ability.
Most electric motors can double or even triple their continuous duty horsepower for short bursts provided they are allowed to rest to cool off between those bursts.
The starter motor that cranks your car engine is a good example of a motor that puts out more horsepower than it can sustain continuously without overheating. It’s task is done in less than 5 seconds and then it can sit there and cool off.
Sometimes with just a slight of hand. Allowing a motor to spin at a higher speed and develope more horsepower means little if you seldom use that range. We had this discussion somewhat, a time ago and I tried ( unsuccessfully as usual) to point out that tractors have little to do with torque ratings and more to do with horse power.
The difference between a car and a tractor ( other then one being a diesel obviously) is that the horse power rating is given in the say, 2600 range where the PTO does all of it’s work at about 540 rpm. For a tractor manufacturer to quote a horse power rating of 50 for example at 3500 rpm vs 40 for some one else at 2500 rpm would probably get him laughed out of the room. It means little to potential buyers unless they know the gearing too and are happy with a diesel doing 3500 while the PTO spins at 540.
Yet, we as car owners all get excited over 305 hp at 6800 rpm. Who the heck is using it ? And, this is for a truck of all vehicles. IMho, that’s why torque has become more meaningful to many. If we treated horse power with the same respect and quoted it within our normal working range, we might take it more seriously…like we do with other applications…tractors, generators etc. are all hp rated and torque numbers are not usually in the discussion.
I’m curious @dagosa. Under what driving conditions would a Nissan Altima be utilizing 300+ horsepower? And more importantly could anyone driving on public roads drive at the 300+ horpower rating for even 10 seconds?
@RodKnox. My point exactly. The “new” Colorado has a 305 hp motor at a very high rpm. My Tacoma is rated at 236 hp at over 1500 fewer rpm. The Colorado has a six speed trans, the Tacoma a five speed. The towing limits are within 500 lbs ( 6500 vs 7000) and the 0 to 60 times are within .3 seconds ( 7.7 vs 7.4 ) est. So, where is this 70 extra horsepower used…to go 115 mph instead of 105 mph probably on the Autobahn. Horsepower numbers for cars, and now trucks, have become a rating that’s difficult to compare and almost meaningless…and that’s too bad. IMho, that’s why many have an “infatuation” with torque…at least it’s a comparison within a “sane” working range. The PTO on a tractor and the limited working range of a generator have a way moderating the range so HP then becomes more meaningful. So, your Altima may never realize the advantage.
Is the “new” Colorado perhaps simply somewhat heavier than your Tacoma? Weight matters when it comes to zero to 60 acceleration.
Why else would my motorcycle with 32 horsepower and around 19 ft lb of torque be able to go from zero to 60 in around 6 seconds or so?
It seems to me that there is not only a general bloat when it comes to power but also the weight of cars and trucks is being bloated to match, pretty much cancelling out any benefit from the higher horsepower.
The Nissan Altima with “300+ HP”. By itself that really doesn’t tell me much. If the car weighs upwards to 5000 pounds, it’s going to be left behind at intersections by 30 horsepower motorcycles.
Put that motor in a 1600 pound roadster and it will leave 30 horsepower motorcycles in its dust.
“I just think KW is more honest because it works for me,it gives me an idea of what the engine is truly capable of,didnt know a human could generate a HP(thought champion cyclists could do maybe 0.4) anyway a sq meter of good PV array will generate on the order of 750 watts(or convert sunlight to electricity)on a bright day,wow,close to a HP(can get my teeth in that one!)suddenly the future is a bit brighter.”
@kmccune, You realize these are directly comparable figures, right? 1HP= 3/4 KW and 1KW = 1.33 HP. The fact that one is defined as 550 Ft*Lb/sec (and the other is defined in joules/sec, right?) is a historical footnote. A fit adult male human can output > 1HP in a short burst fairly easily, but will quickly get winded working that hard. A horse can output 1HP over a 40-hour work week–a completely different thing.
(I found HP much more convenient than KW when I was setting up gear ratios on my bicycle. Assuming:
Max weight of bike+rider+gear = 275#
Max output (for 10 min duration or less) = 1/3 HP
I calculate that I can pedal up a hill at 0.67 ft/sec vertical gain. If I knew the max road gradient on my trip, I can figure out what gear ratio will let me spin at least 60 RPM in doing so!)
