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You know, of all the tutorials I've read online, I still don't get the difference between HP and TQ. I have somewhat of an idea, but it's very blurry. Can someone clarify this matter? I try to think really really hard but I still don't understand =) I know Torque is defined as a turning or twisting force, that's fine... measured in foot pounds (the force exerted on an object at a 90 degree angle at one foot -- if i'm notmistaken) and horsepower... something about moving 33lbs one foot in one minute. But how does this all relate to the power an engine makes? And whats better? A car with 500lbs of tq and 100 HP, or a car with 500 HP and 100 lbs of tq? (i know its probably not possible, but you get my drift) Who has the advantage?

 
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i think i understand it a little... torque, is how hard the horsepower is put to the wheels. thus most highly tuned cars are like 450 hp and 500 torque, but i could be wrong...

 
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The way that I understand it it that TQ is what gets you going. HP is what keeps you going faster. A car with 500 lbs TQ and 100 HP will have a good start off the line but will not get the same speed as a 500 HP car. A car with 500HP and 100 lbs TQ won't have that great of a start off the line but with time it will be traveling faster than a car with 100 HP.

Think about this a Z24 and a 00 and earlier SI had about the same 1/4 mile times. The Z24 had 150 HP and 155 lbs TQ. The SI had 160 HP and (135/140 lbs TQ [IMG]i/expressions/face-icon-small-confused.gif[/IMG] ). I had seen very few and I mean few SI that can beat a Z24 in the 1/8 of a mile but in the 1/4 mile is a different story.

Lastly HP is derive by torque. TQ and HP are the same at 5200 rpms.

 
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The way I understand it is that if you have a car that has 500lb of torque and 100hp. then you are better at short distances such as quarter mile times. The 500hp and 100lb of torque would be better at mid range and top speed. I could be way off and if so, I would love for someone to correct me.

 
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Another way to think about this is to look at heavy duty trucks. If you notice they have LOTS of TQ and not as much HP. The reason for this is that the amount of TQ will help them move all the weight that they are pulling.

 
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It's all about torque curve. If you make all your torque low in the rpm range, yoy'll have no horsepower and your speed will suffer dramatically (diesel motor). You can jump off the line, but that's all you do.

If you move all your torque up high in the rpm range (high revving motor), you'll dog at the line unless you rev the heck out of the motor. However, once you get into the torque range high in the rpm range, you'll be hauling ***.

Think about the difference between a harley and a sport bike. Both can make the same horsepower (on the order of 100 hp). The harley, with it's low torque range, can jump off the line for about 5 feet, then it's done. A sport bike has to rev to 5,000 rpm and dump the clutch to get it to jump off the line. Once it's moving though, lights out for the harley, it's left in a cloud of dust as the sport bike revs to 10,000 rom. The harley needs more torque to make the same horsepower as the sport bike because it makes the horsepower lower in the torque curve.

It's all about torque curve, baby...

 
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This has nothing to do with anything, but the '00 Civic Si had 111 lbs of torque.

OK...GAME ON!!!

 
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Horsepower is measured from Torque. That's how the Dyno works... it measures the torque your wheels put in the rollers, then runs it through the equation
Horsepower=Torque*RPM/5252.
Your engine has more torque that HP below 5252, and more HP than torque above 5252. That's why lots of torque leads to low end, but you need the HP to keep the car going once the RPMs run up. When you're looking at advantages of more torque VS HP, it's relative. A car that generates 500 ft-lb of torque at 1500 RPM and doesn't maintain it is pretty useless. The key is to maximize the time you spend near the top of your torque curve... then the HP will go with it. Look at the M3 for example... it pulls almost constantly from 2500 or so all the way to the redline.
The funny thing is we have a torque-biased engine (more stroke than bore), and we still make more HP than torque.
Numbers don't tell the whole story... you need to be able to hold those values as well. I don't know that I've ever seen a Z24 dyno chart, but the if I remember right, the B16 holds almost max torque for a while once it reaches it, which brings the horsepower up with it. Since power is time dependent, the longer you can hold the maximum force you're applying (torque) the more power you can generate.

 
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Basically you drive torque but the dealer sells you HP. HP= (TQ*RPM)/5252. Thats how you figure out HP. You can have more TQ than HP if the max TQ is at a lower RPM. 5252 is the number where the TQ and HP graph cross each other. But other than that there really is no relation. Honda engines have max TQ at a high RPM so thats why they have such high HP numbers.

 
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I'm not very clear with all this explanations, so basicly, torque = acceleration and HP = top speed??

 
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horsepower is derived from torque...all it is, is a way to express torque and rpm together.

 
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i've just always heard that tq wins races, not hp.

 
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Torque is the rotating force. Horsepower is a unit of power, which is force/time. Force = mass * acceleration. Horsepower is derived from torque * speed of rotation (RPM). So horsepower is the rate at which torque is applied.

 
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To be honest with you, torque is a decent measurement of power... but it is misleading. The reason you look at horsepower and people talk about horsepower, is because it gives you a BETTER idea of the performance of a car. If we all looked at torque, we would be wrong in our assumptions. Now horsepower isn't the end all, since weight plays a factor, as well as torque curve... or even more so WHERE the power is being made.

That's the reason HP is such a big deal. And no, torque doesn't win races, but HP will give you a better idea of what kind performance you can expect, and hp/weight an even better idea.

Let's take an example.

Mustang GT and S2000 is one of the classics that's always good at making this point.

153 lb/ft and 2,650lbs VS 302 lb/ft and 3,300lbs.

2650/153 = 17.32
3300/302 = 10.92

Now looking at torque and weight, you would think the S2000 would get it's but kicked and hard! But that's not the case... in fact, the S2k is slightly faster than a Mustang GT. So let's take a look at horspower numbers....
2650/240 = 11.04
3300/300 = 11.00

Now that makes a bit more sense. Now throw in power curve, and the fact that the S2k's power is up top (which is where you spend most of the 1/4 mile) you see why the S2k is slightly faster. So HP isn't just some number we should all ignore. If you really WANT to look at torque, you have to look at gearing, wheel torque, weight, and wheel circumference.

 
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So basically S2000man01, what matters is in what RPM range the motor will spend its time running through the gears and also the cars weight. The Mustang GT shows that it has a higher TQ/weight ratio...so that means it takes off quicker, but when racing, that power isnt as efficiently applied as the S2000's? Good explanations guys, so I take it this is the bottom line: Torque is a measurement of an engine's power ALL BY ITSELF. But HORSEPOWER takes into account engine speed and weight and makes ANOTHER unit of power which describes HOW well torque can move the car when you take into account torque gearing and so forth? Still a tiny bit confused..... why do Honda engines, in general, always produce low torque numbers? Is that necessarily a good thing? Is it just Honda's high revving engine building philosophy that helps achive high HP #s? What if Ford made high revving V8s? I just threw in there like 10 milliontheories...just trying to understand this better.

 
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Here's a text book answer:
Power (such as horsepower) is a measurement of Work/Time. Work is Force*Distance.

Torque is Force*Torque Arm. For example, if you have a 3 meter pole with a pivot at one end and you apply 5 Newtons an the other end, then you will have 15 Newton*Meters of Torque.

Thus, Power is the ability to do work and Torque is rotational energy. So, if you have no torque, then you will not be able to get off the line simply because you do not have the ability to turn your wheels. If you have no power, then you will not be moving. So, when you ask about 500 torque or 500 horsepower. Basically, it depends on the weight of the car and the diameter of its wheels. If it is light weight with a small diameter, then the 500 hp car will win. However, if it's a heavy car with larger wheels, then the 500 torque will be a better choice. However, this only applies for smaller distances such as quartermiles. For very long distances, it is the other way around. Basically, you can think of it this way:
500 torque + 100 hp is like driving your car in 1st gear only
500 hp + 100 torque is like driving your car in 5th gear only
As you can probably tell, the first one will be great for getting off the line, but the second would be great for high speeds.

So, over all, in racing terms, torque will get you off the line and horsepower will make you go fast.

 
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ok, here's the down and dirty, horsepower is how much work the engine is doing.
Horsepower, as stated earlier is a function of torque.

So, the higher the horsepower, the more work the car is doing per minute, and work equates to a change in momentum, therefore, more horsepower means higher top speed, and better acceleration. 1 horsepower equals 33,000 foot-pounds of work in one minute, so moving 33,000 pounds of wieght 1 foot in 1 minute, (33,000lbs X 1Ft X 1 Minute) or anything multyplied together to get 33,000.

So, if an engine produces 100 ft/lbs of torqe, and is running at 2000 rpms, then it would be making (100 X 2000)/5252 = 38.09... Horsepower. the number 5252 comes from a series of conversion that aren't really important so we'll just ignore that. So, if your engine produces 500 ft/lbs of torque and only 100 horsepower, that means that it doesn't rev very high, (big v8 motor) The reason why these produce so much torque is because of they have a long stroke, therefor it's a bigger lever operating on the crank shaft, but since it's bigger it can't rev as high because it will break.

ANYWAY, getting off topic, but torque has nothing directly to do with "launching you" it is all to do with the horsepower, since that's what is actually moving your car, SO for the best launch of your car, you want to drop the clutch at the peak horsepower, the reason why we don't usually do this is because are tires would just sit there spinning. The reason why high torque helps, is that it allows a greater gear ratio to be used, which lets you accelerate quicker.

Now you ask "then why don't trucks have small engines that rev high if torque does't matter" The reason for this is that if trucks were driving around at 6000 RPMS they'd break down pretty readily, also as mentioned above, they'd need very short gears because the small engine wouldn't have the power to turn a taller gear.

WITH all that being said, I probably confused more of you then I helped, I'll re-edit this, and post a excell spread sheet that will clear things up.

-Mark

Edit: I attached a spreadsheet, you have to rename it to .xls though cause it wouldn't let me upload it otherwise...