yea thats why people love gears so much cause it makes u feel like u have more torque, like jb said with the math things
hp or tq
- Thread starter shttygtstang
- Start date
Alright fellas, hopefully I can shead some light on this. I wondered about the same thing and had the same questions before and i've read about it and learned enough to help me understand. Torque is what gets you moving, but it's also what keeps you going: Horsepower is a function of torque. Without torque, you have no horsepower...period. The theoretical example of a 1000 hp motor w/ "no torque" is not possible. Here's the formula: Torque=(HP*5252)/RPM. Example...if your car has 220 hp at 4000 rpm, your torque is 288 lbs/ft. Dig? Don't get this confused with "200 hp at 4000 rpm, 300 lbs/ft at 3400 rpm" or something similar...to calculate torque or horsepower, you have to use both at the same rpm....you just generally have max torque at a lower rpm than HP - as far as I know.
You ever see the "250 hp" imports or whatever? That's fine, well, and dandy, but since they're smaller displacement motors, they have to rev a lot higher than we do, so they're hitting that 250 hp at say 7500 rpm (i'm making these figures up, but they should be close - the math is correct though). ((250HPx5252)/7500RPM)=175TQ. Get it? Since Torque is what gets you started, you'd kill that import in a drag race. Race from a roll and he'd have more of a chance, which is why a lot of them prefer to race from a roll or race to top speed, etc.
You ever see the "250 hp" imports or whatever? That's fine, well, and dandy, but since they're smaller displacement motors, they have to rev a lot higher than we do, so they're hitting that 250 hp at say 7500 rpm (i'm making these figures up, but they should be close - the math is correct though). ((250HPx5252)/7500RPM)=175TQ. Get it? Since Torque is what gets you started, you'd kill that import in a drag race. Race from a roll and he'd have more of a chance, which is why a lot of them prefer to race from a roll or race to top speed, etc.
89CopCoupe
Banned
Michael Yount
Mustang Master
Boy, there's lots of 'stuff' in here. It's very difficult to convey in words alone the difference between these two measures. That's why there's so much confusion about them. There is also quite a bit of terminology mis-use in this thread. To everyone that's posted - I'd suggest you do a Google search under "horsepower vs. torque" and spend some time reading. Pay attention to how the terms power, torque, force and work are defined in terms of physics. There's an almost infinite amount of info out there about this. I believe this one sums it up the best during my quick search -- http://www.westechperformance.com/pages/Tech_Library/Understanding/hpvstq.html (edit: the piece I'm referring to is the beginning of the article where descriptions of HP/Torque are provided; as you read on there are statements made about other things that 'experts' might disagree about)
Quick summary - torque is a measure of a twisting force - measured in lb-ft, or a force (in pounds) applied over a lever arm (in feet). HP is a measure of power - or a force applied over some unit of time. When the force applied is a twisting force and it's applied over time, and movement actually occurs, the two are related (the equation was listed above - Torque=(HP*5252)/RPM). If you examine both together over the operating range (rpm) of a particular engine, you will have some idea of the performance characteristics of that engine. However, that's not the whole story. The traction that's available to put the torque to the ground, the gearing that's available to keep the engine working in the fattest part of it's torque curve, and the weight of the vehicle being accelerated all play a part in determining just how quickly the vehicle will accelerate and for how long it will keep accelerating that quickly.
The biggest problem I think is that people look at simply peak numbers - my engine makes X HP and Y torque. That really doesn't tell you much. Knowing at what rpm those peaks occurred starts to help paint a picture. But the problem remains that both numbers vary constantly with rpm - and rpm is usually varying constantly. So you really need to see a graph of how the torque and Hp produced vary with rpm to get a feel for how the engine is gonna react.
In general, as vehicles get heavier, the vehicles that are gonna be the most responsive and fun to drive are those that produce the highest AVERAGE torque figures in the rpm range that you spend most of your time in. As vehicles get lighter, the lack of a bunch of torque at low rpm is less of an issue in terms of the car feeling responsive. Also in general - for cars of a similar weight and with similar traction if they're geared to take advantage of their HP and torque curves - the one that puts down the highest average torque during the period of acceleration will accelerate the quickest, and the one the puts down the highest average HP during the period of acceleration will achieve the highest speed at the end of the acceleration. Clear as mud? Said another way - and again, generalizing - bigt torque numbers will get you moving quicker sooner; big HP numbers will keep you moving quicker longer. And, the faster you're going, the more that aerodyamic drag plays into performance - even more than the weight of the vehicle (another benefit of keeping things smaller and lighter). You want to accelerate quickly through the quarter? Pay close attention to high average torque being available over the rpm range you're using during the run. You want highest top speed? Pay close attention to peak HP, and gear the car so the engine's revving where that peak HP number is produced at the top speed.
The original question had to do with which is more important, and how should the engine be built. And the answer is that it depends on what you're trying to accomplish with the car. For a light car that will only be raced on the track - low rpm torque is less of an issue - because of the car's weight, and because at the track, you can operate the engine in a higher rpm range - where more torque and power are available. As the vehicle's weight goes up, and/or the engine's operating rpm range comes down - and that's what happens with most street cars (they're heavier and they spend more time at lower rpm) - having significant torque available over a wider range of lower rpm becomes more important IF you want to the car to be responsive with smaller throttle openings, and without revving it like crazy.
I knew I was building a street car and I wanted it to be very responsive at low rpm and get reasonable gas mileage. Consequently, I didn't pay any attention at all to making a big peak HP number. I asked my cam designer to help put together a package that made peak torque below 4000 rpm, and peak HP below 5000 rpm - cause I knew I'd spend very little time up there. And I asked for a broad, flat torque curve - with lots of torque available at very low rpm (off-idle). That's what we ended up with - and I've got an engine that doesn't really care what gear I'm in around town - just step on the gas and it squirts forward with authority. I don't have to rev it above 5000 to get good performance. And it gets around 18 mpg city/24mpg highway (a little better if I really try) in a car that weighs about 3300 lbs. with me in it, and with the aerodynamics of a brick. That's what I was after.
Quick summary - torque is a measure of a twisting force - measured in lb-ft, or a force (in pounds) applied over a lever arm (in feet). HP is a measure of power - or a force applied over some unit of time. When the force applied is a twisting force and it's applied over time, and movement actually occurs, the two are related (the equation was listed above - Torque=(HP*5252)/RPM). If you examine both together over the operating range (rpm) of a particular engine, you will have some idea of the performance characteristics of that engine. However, that's not the whole story. The traction that's available to put the torque to the ground, the gearing that's available to keep the engine working in the fattest part of it's torque curve, and the weight of the vehicle being accelerated all play a part in determining just how quickly the vehicle will accelerate and for how long it will keep accelerating that quickly.
The biggest problem I think is that people look at simply peak numbers - my engine makes X HP and Y torque. That really doesn't tell you much. Knowing at what rpm those peaks occurred starts to help paint a picture. But the problem remains that both numbers vary constantly with rpm - and rpm is usually varying constantly. So you really need to see a graph of how the torque and Hp produced vary with rpm to get a feel for how the engine is gonna react.
In general, as vehicles get heavier, the vehicles that are gonna be the most responsive and fun to drive are those that produce the highest AVERAGE torque figures in the rpm range that you spend most of your time in. As vehicles get lighter, the lack of a bunch of torque at low rpm is less of an issue in terms of the car feeling responsive. Also in general - for cars of a similar weight and with similar traction if they're geared to take advantage of their HP and torque curves - the one that puts down the highest average torque during the period of acceleration will accelerate the quickest, and the one the puts down the highest average HP during the period of acceleration will achieve the highest speed at the end of the acceleration. Clear as mud? Said another way - and again, generalizing - bigt torque numbers will get you moving quicker sooner; big HP numbers will keep you moving quicker longer. And, the faster you're going, the more that aerodyamic drag plays into performance - even more than the weight of the vehicle (another benefit of keeping things smaller and lighter). You want to accelerate quickly through the quarter? Pay close attention to high average torque being available over the rpm range you're using during the run. You want highest top speed? Pay close attention to peak HP, and gear the car so the engine's revving where that peak HP number is produced at the top speed.
The original question had to do with which is more important, and how should the engine be built. And the answer is that it depends on what you're trying to accomplish with the car. For a light car that will only be raced on the track - low rpm torque is less of an issue - because of the car's weight, and because at the track, you can operate the engine in a higher rpm range - where more torque and power are available. As the vehicle's weight goes up, and/or the engine's operating rpm range comes down - and that's what happens with most street cars (they're heavier and they spend more time at lower rpm) - having significant torque available over a wider range of lower rpm becomes more important IF you want to the car to be responsive with smaller throttle openings, and without revving it like crazy.
I knew I was building a street car and I wanted it to be very responsive at low rpm and get reasonable gas mileage. Consequently, I didn't pay any attention at all to making a big peak HP number. I asked my cam designer to help put together a package that made peak torque below 4000 rpm, and peak HP below 5000 rpm - cause I knew I'd spend very little time up there. And I asked for a broad, flat torque curve - with lots of torque available at very low rpm (off-idle). That's what we ended up with - and I've got an engine that doesn't really care what gear I'm in around town - just step on the gas and it squirts forward with authority. I don't have to rev it above 5000 to get good performance. And it gets around 18 mpg city/24mpg highway (a little better if I really try) in a car that weighs about 3300 lbs. with me in it, and with the aerodynamics of a brick. That's what I was after.
blackstangt
Member
Torque an horsepower are the same thing but two different ranges. 1 ft/lb of tq is equal to 1 hp at 5252rpm. you want the max hp at the lowest rpm possible, with these cars, you want low end hp, because their torque range is so powerful as it is, if you can get more peak hp at the same or lower hp, it is better than adding that much torque at anything below 5252 rpm. Torque is fun, but horsepower will keep you accelerating throughout the powerband.
Michael Yount
Mustang Master
"Torque an horsepower are the same thing but two different ranges."
That statement isn't any more accurate than saying that height and weight are the same thing, but they start with a different first letter. When people refer to the fact that HP and torque are equal at 5252 rpm, that does not mean Hp and torque are the same thing. Torque is a measure of twisting force. HP is a measure of ability to sustain that twisting force over time. Two completely different things. Torque's units are pound-feet; HP's units are pound-feet/second. Very different.
That statement isn't any more accurate than saying that height and weight are the same thing, but they start with a different first letter. When people refer to the fact that HP and torque are equal at 5252 rpm, that does not mean Hp and torque are the same thing. Torque is a measure of twisting force. HP is a measure of ability to sustain that twisting force over time. Two completely different things. Torque's units are pound-feet; HP's units are pound-feet/second. Very different.
oz
Founding Member
As any good racing engine builder will tell you, you want to maximize the torque in the operating range of the engine - end of story. Determine what operating range you want to run in and build the engine to excel (i.e. run at maximum volumetric efficency) at that RPM.
Another very important thing to remember is this:
Horsepower CAN NOT BE MEASURED... it is derived from the formula given earlier. When you have your car dyno'd the dyno measures the torque and then CALCULATES the HP. It is the same equation for any engine.... My riding lawn mower has 12 hp at 1600 rpm.... therefore they must have MEASURED that it has 39.39 ft lbs of torque at 1600 rpm and CALCULATED the hp to be 12.
What the HP formula also means is this:
1. The horsepower rating will ALWAYS be less than the torque rating at EVERY RPM below 5252.
2. The horsepower rating will ALWAYS be more than the torque rating at EVERY RPM above 5252.
3. The horsepower rating and the torque rating will ALWAYS be EQUAL at 5252 rpm (i.e the dyno curves cross).
No if's and's or buts.
In practice:
Ricers have high reving engines - their maximum hp rating is usually above 5252... - makes sense that they don't have very good torque numbers.
Toyota Celica - 190 hp at 6800 rpm = 146 ft lbs of torque.... not too impressive.
Diesels make power at very low rpms - 600 ft lbs at 1600 rpm = 182.8 hp. lots of grunt but not great accelerators unless they can stay near this rpm when accelerating by shifting a lot. (They usually can not and inherently have a very narrow power band - thus 10+ speeds on big rigs)
My Mustang makes 326 tq at 4000 rpm = 248 hp
At 5200 my Mustang makes 287 hp = 290 tq (less than at 4000 rpm but due to the fact that the HP CALCULATION takes in to account RPM, the HP number is inflated)...
Does any of this make sense? Just remember the equation and that Torque is king and you will be fine.
Another very important thing to remember is this:
Horsepower CAN NOT BE MEASURED... it is derived from the formula given earlier. When you have your car dyno'd the dyno measures the torque and then CALCULATES the HP. It is the same equation for any engine.... My riding lawn mower has 12 hp at 1600 rpm.... therefore they must have MEASURED that it has 39.39 ft lbs of torque at 1600 rpm and CALCULATED the hp to be 12.
What the HP formula also means is this:
1. The horsepower rating will ALWAYS be less than the torque rating at EVERY RPM below 5252.
2. The horsepower rating will ALWAYS be more than the torque rating at EVERY RPM above 5252.
3. The horsepower rating and the torque rating will ALWAYS be EQUAL at 5252 rpm (i.e the dyno curves cross).
No if's and's or buts.
In practice:
Ricers have high reving engines - their maximum hp rating is usually above 5252... - makes sense that they don't have very good torque numbers.
Toyota Celica - 190 hp at 6800 rpm = 146 ft lbs of torque.... not too impressive.
Diesels make power at very low rpms - 600 ft lbs at 1600 rpm = 182.8 hp. lots of grunt but not great accelerators unless they can stay near this rpm when accelerating by shifting a lot. (They usually can not and inherently have a very narrow power band - thus 10+ speeds on big rigs)
My Mustang makes 326 tq at 4000 rpm = 248 hp
At 5200 my Mustang makes 287 hp = 290 tq (less than at 4000 rpm but due to the fact that the HP CALCULATION takes in to account RPM, the HP number is inflated)...
Does any of this make sense? Just remember the equation and that Torque is king and you will be fine.
bluevenom867
I will have images of molesting stuffed animals in
You need torque.
With out torque hp doesn't exist.
Torque is a twisting/turning force.
So take a piece of pipe and try to turn it with out useing any force.
Not possable, is it?
If you had an engine with no torque it would not even be able to start.
With out torque hp doesn't exist.
Torque is a twisting/turning force.
So take a piece of pipe and try to turn it with out useing any force.
Not possable, is it?
If you had an engine with no torque it would not even be able to start.
Michael Yount
Mustang Master
....And to confuse matters even more - this all applies to internal combustion engines whose output turns a shaft. Electric motors produce their peak torque at ZERO rpm..... 
Also, just to clarify - HP and torque can never really be "equal" because they are different quantities measured in different units. But because of the math, the 'number' of lb-ft (torque) is equal to the number of lb-ft/sec (HP) at 5252 rpm.
Dynos that can apply a load to the engine/chassis measure torque, and calculate HP. Inertial dynos (like the popular Dynajets) actually do approximate HP and calculate torque. Built into the inertial dyno's programming are tables that 'know' how much power it takes to accelerate a known mass (the 8000 lb. rollers) to a certain speed in a certain amount of time. By looking at instantaneous acceleration rates, they 'measure' HP, and then they calculate torque based on the equation. There are some dynos that can be used in either inertial or load-based modes.
Also, just to clarify - HP and torque can never really be "equal" because they are different quantities measured in different units. But because of the math, the 'number' of lb-ft (torque) is equal to the number of lb-ft/sec (HP) at 5252 rpm.
Dynos that can apply a load to the engine/chassis measure torque, and calculate HP. Inertial dynos (like the popular Dynajets) actually do approximate HP and calculate torque. Built into the inertial dyno's programming are tables that 'know' how much power it takes to accelerate a known mass (the 8000 lb. rollers) to a certain speed in a certain amount of time. By looking at instantaneous acceleration rates, they 'measure' HP, and then they calculate torque based on the equation. There are some dynos that can be used in either inertial or load-based modes.
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Michael Yount said:....And to confuse matters even more - this all applies to internal combustion engines whose output turns a shaft. Electric motors produce their peak torque at ZERO rpm.....
Also, just to clarify - HP and torque can never really be "equal" because they are different quantities measured in different units. But because of the math, the 'number' of lb-ft (torque) is equal to the number of lb-ft/sec (HP) at 5252 rpm.
Dynos that can apply a load to the engine/chassis measure torque, and calculate HP. Inertial dynos (like the popular Dynajets) actually do approximate HP and calculate torque. Built into the inertial dyno's programming are tables that 'know' how much power it takes to accelerate a known mass (the 8000 lb. rollers) to a certain speed in a certain amount of time. By looking at instantaneous acceleration rates, they 'measure' HP, and then they calculate torque based on the equation. There are some dynos that can be used in either inertial or load-based modes.
are you saying we should all be drag racing with electric motors.you blew my mind. also why does lets say my eclipse make more tq then hp or its about the same.why do some people sacrifice tq on perpose to gain hp
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RydeOn said:
ide cry if my that bike only made 120 hp.it pulls a 8.4 with no n20 in the 1/4 mile and never had a run with it because of traction issues
Michael Yount
Mustang Master
If you can power them, electric motors rock - 20 years from now you guys kids (my grandkids) will be modding the hybrids - and they'll scream!
Your eclipse was boosted - different animal when it comes to torque/hp curve characteristics than naturally aspirated. I'm off to the movies (Bourne) -- someone else can take a stab at what happens to relative curves where boost is involved.
Your eclipse was boosted - different animal when it comes to torque/hp curve characteristics than naturally aspirated. I'm off to the movies (Bourne) -- someone else can take a stab at what happens to relative curves where boost is involved.
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blackstangt
Member
I saw a show with an electric car that destroyed the 500 hp viper in a race, but it weighed like 1800 lbs. Not Fair by weight, but it was fast.
- Jun 2, 2004
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_jb_
New Member
I dont' know if it's the undercoating stuff I used about a half hour ago or if its this thread that is giving me a headache lol
Michael Yount
Mustang Master
bluevenom867
I will have images of molesting stuffed animals in
Maybe we should just put a jet engine in our stangs(Volvo's) and forget about hp and torque.
Thrust baby!
Thrust baby!
Nice job oz - Mike did a good job too.
HP is the ability of an engine to maintain torque as rpm increases. The ability to maintain torque depends on the ability of the engine combination to fill the cylinder with the same amount of air/fuel. As rpm increases, it becomes harder for the short valve events to let enough air/fuel into the cylinder to get the same torque from combusting the mixture. Ever notice how in some engines past the 5252 rpm mark that the torque is falling off but the HP is still climbing?
HP is the ability of an engine to maintain torque as rpm increases. The ability to maintain torque depends on the ability of the engine combination to fill the cylinder with the same amount of air/fuel. As rpm increases, it becomes harder for the short valve events to let enough air/fuel into the cylinder to get the same torque from combusting the mixture. Ever notice how in some engines past the 5252 rpm mark that the torque is falling off but the HP is still climbing?
