Lexus: Horsepower vs. Torque
09-23-12, 09:11 AM
#48
In the U.S. the Society of Automotive Engineers (SAE) has, since 1903, defined one horsepower as the ability to lift 33,000 pounds one foot in one minute, or 550 pounds one foot in one second.
In Germany, however, the horsepower was established as the ability to lift 45,000 kg (there are 0.4536 kg to the pound) one centimeter (2.54 cm to the inch) in one minute, which translates to 98.629% of an SAE horsepower, and you'll just have to trust us with the math. The Germans, by the way, standardized the horsepower through a system of measurement called "JS," the abbreviation for the German term for horsepower, now classified as "DIN."
In Germany, however, the horsepower was established as the ability to lift 45,000 kg (there are 0.4536 kg to the pound) one centimeter (2.54 cm to the inch) in one minute, which translates to 98.629% of an SAE horsepower, and you'll just have to trust us with the math. The Germans, by the way, standardized the horsepower through a system of measurement called "JS," the abbreviation for the German term for horsepower, now classified as "DIN."
09-23-12, 09:20 AM
#49
In the U.S. the Society of Automotive Engineers (SAE) has, since 1903, defined one horsepower as the ability to lift 33,000 pounds one foot in one minute, or 550 pounds one foot in one second.
In Germany, however, the horsepower was established as the ability to lift 45,000 kg (there are 0.4536 kg to the pound) one centimeter (2.54 cm to the inch) in one minute, which translates to 98.629% of an SAE horsepower, and you'll just have to trust us with the math. The Germans, by the way, standardized the horsepower through a system of measurement called "JS," the abbreviation for the German term for horsepower, now classified as "DIN."
In Germany, however, the horsepower was established as the ability to lift 45,000 kg (there are 0.4536 kg to the pound) one centimeter (2.54 cm to the inch) in one minute, which translates to 98.629% of an SAE horsepower, and you'll just have to trust us with the math. The Germans, by the way, standardized the horsepower through a system of measurement called "JS," the abbreviation for the German term for horsepower, now classified as "DIN."
09-23-12, 11:58 AM
#50
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If you could design two engines that have the same maximum HP output, but very different torque - say one producing 100lb/ft with 200hp and the other one producing 500lb/ft with the same 200hp, and put them into exact same cars and design gearing that allows for the fastest acceleration and highest top speed - the two cars will accelerate exactly the same and reach exact the same top speed. No matter what the amount of torque is, an engine will provide maximum acceleration at the RPM range where its making the most HP - and if you could design gearing that always keeps the engine RPM where its making 95-100% of its HP both cars will accelerate and feel exactly the same, just one is going to stay at say 2k RPM and the other will stay at 10k. Obviously this will require a ridiculous amount of gears or a very tricky CVT with a wide range of gear ratios, therefore its very unpractical and can't really be made for real world applications.
Also, what I said is only true if these engines weighed the same, were mated to transmissions that were of the same weight, and shifts between gears were instant.
Also, what I said is only true if these engines weighed the same, were mated to transmissions that were of the same weight, and shifts between gears were instant.
that's exactly my point. with ideal transmission and similar weight, it is the peak HP that matters and torque has nothing to do with the performance of the car. a higher HP car will always be faster, and quicker.
it amazes me how many people have wrong concept of how stuff works. even this lexus
speaker..
1st of all. horse power is a unit of energy.
2nd of all, hours power over time is work.
Last edited by seanlee; 09-23-12 at 12:03 PM.
09-24-12, 10:38 AM
#52
i guess the misunderstanding is from whether it is wheel torque or engine torque.
from the wheel point of view.
E= torque X angle moved. as you can see, to move faster or reach higher speed, you need more Energy.
and engine of the car provides torque at a giving RPM, which is the energy, and its unit is HP (or watt). the torque of the engine at certain RPM has little meaning because it will be re covered by shift gears. the wheel torque can be manipulated by gearing. However, something you cannot manipulate is energy because conservation of energy (unless you bring in quantum physic). that is, giving a fix amount of energy, you can have more torque, or rotate faster. if you want more torque and rotate faster? get more energy.
of course, the feeling of acceleration is actually over a period of time, which is Work (N). and work is a integration of energy over time. to speak from engine point of view, it is the HP produced over a period. this period just happens to be when engine revs from low to high, and since HP is a product of Rev and Torque, one could also say it is a torque curve. . However, the fact stays: more HP gives your more wheel torque at the certain wheel speed. most car has torque curve rather flat, so a torque value gives your a idea of how much "push" you can feel. ( while HP will increase in linear as engine RPM goes higher, you won't feel that because your car is also rotating at higher speed so your 'feel' stay the same).
technically, you could throw the entire "torque curve" out of the window if you car has electric engines. ideally, your engine will be producing constant (HP) and the CVT should cover that to speed or wheel torque. if you look at some electric bus, there is no "torque curve", it is a straight line.
with CVT, the torque curve on the ICE car is actually a lot less meaningful. take maxima for example. when you push it, the engine stays at a constant RPM (where maxim HP is produced), your car accelerate by the change of ratio in CVT. the torque curve of the VQ35 engine, in this case, is entirely useless, the car can have 20 lb ft of torque from 1500 to 5000 for all i care, and it will be just as fast as long as the maximum HP is the same. (well, that is if we hold the break and release the car when engine reaches desired RPM)
anyways. a 1000 HP car with 200 lb ft of torque engine, if driving and geared property, will beat 1000 lb ft of torque but 200 HP engine all day everyday.
if you have different opinion, say it scientifically instead of " i am an engineer". as a fellow engineer and Master in engineering degree, i thought you know better.
from the wheel point of view.
E= torque X angle moved. as you can see, to move faster or reach higher speed, you need more Energy.
and engine of the car provides torque at a giving RPM, which is the energy, and its unit is HP (or watt). the torque of the engine at certain RPM has little meaning because it will be re covered by shift gears. the wheel torque can be manipulated by gearing. However, something you cannot manipulate is energy because conservation of energy (unless you bring in quantum physic). that is, giving a fix amount of energy, you can have more torque, or rotate faster. if you want more torque and rotate faster? get more energy.
of course, the feeling of acceleration is actually over a period of time, which is Work (N). and work is a integration of energy over time. to speak from engine point of view, it is the HP produced over a period. this period just happens to be when engine revs from low to high, and since HP is a product of Rev and Torque, one could also say it is a torque curve. . However, the fact stays: more HP gives your more wheel torque at the certain wheel speed. most car has torque curve rather flat, so a torque value gives your a idea of how much "push" you can feel. ( while HP will increase in linear as engine RPM goes higher, you won't feel that because your car is also rotating at higher speed so your 'feel' stay the same).
technically, you could throw the entire "torque curve" out of the window if you car has electric engines. ideally, your engine will be producing constant (HP) and the CVT should cover that to speed or wheel torque. if you look at some electric bus, there is no "torque curve", it is a straight line.
with CVT, the torque curve on the ICE car is actually a lot less meaningful. take maxima for example. when you push it, the engine stays at a constant RPM (where maxim HP is produced), your car accelerate by the change of ratio in CVT. the torque curve of the VQ35 engine, in this case, is entirely useless, the car can have 20 lb ft of torque from 1500 to 5000 for all i care, and it will be just as fast as long as the maximum HP is the same. (well, that is if we hold the break and release the car when engine reaches desired RPM)
anyways. a 1000 HP car with 200 lb ft of torque engine, if driving and geared property, will beat 1000 lb ft of torque but 200 HP engine all day everyday.
if you have different opinion, say it scientifically instead of " i am an engineer". as a fellow engineer and Master in engineering degree, i thought you know better.
I've had to give this 'lecture' to so many gearheads in the past that it becomes tiresome.
09-24-12, 11:08 AM
#53
Except Audi does that in their R18 LMP car that just got completely pwnt by gasoline Toyota. 
https://www.clublexus.com/forums/car...in-brazil.html
https://www.clublexus.com/forums/car...in-brazil.html
This does nothing to disprove what I said.
Technically speaking, yes, you can have a high-powered engine that doesn't have much peak torque if it revs high enough, but that's not really a problem as far as performance goes. Just put in some shorter gears, and you now have all the torque you need at the wheels. And in fact, this type of engine may well have some advantages in that it's probably smaller and lighter. That's part of why super-high-revving engines with high HP-to-displacement ratios and low torque are used in F1 cars.
Technically speaking, yes, you can have a high-powered engine that doesn't have much peak torque if it revs high enough, but that's not really a problem as far as performance goes. Just put in some shorter gears, and you now have all the torque you need at the wheels. And in fact, this type of engine may well have some advantages in that it's probably smaller and lighter. That's part of why super-high-revving engines with high HP-to-displacement ratios and low torque are used in F1 cars.
http://en.wikipedia.org/wiki/Audi_R10_TDI
Diesel engines have been used very successfully in Le Mans racing for many years now.
Diesel engines have been used very successfully in Le Mans racing for many years now.
The discussion is obviously about road-going cars, and in the realm of road-going cars, what I said remains true. The alternative of a high-revving otto cycle engine isn't a favorable option because no road-going car is going to hold their engine in a high RPM band at all times, and the transmission that would allow a computer to do so for your daily driver is impractical.
So, to reiterate. We're not talking about driving on a race track. We're talking about what's useable day in, day out, at all engine speeds, in the conditions people encounter in their commute. In which case any example from Le Mans or F1 goes out the window.
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