Horsepower is not a measurement of how much work is done, it is a measurement of how quickly the work is done. The units of work are ft-lbs, which coinsides with the units of torque. When that unit is divided by time we get power. If you push on an object with a force of 55 lbs for 10 ft. you have applied 550 ft-lbs of work. If that distance was covered in 1 second you would have expended 1 hp. If you push on it twice as hard, it accelerates twice as fast, and you cover twice the distance in the same time resulting in 2 hp. When a 200 lb man applies 400 ft-lbs of torque to a breaker bar, he is applying a force. He has not done any work to the bar until it moves.

As for the sport bikes, the Busa engine in a Harley would definitely out run it on the top end, but at low speeds the HD engine will likely have the advantage because it makes more torque at low speeds. IIRC, the Harley peaks at 85 ft-lbs@3000 rpm, the Busa peaks at 102 ft-lbs @ 7000 rpm. We can't accurately predict what will happen because we don't know what the torque curves look like at very low engine speeds. I have serious doubts that the Busa will make 85 ft-lbs or more at 3000 rpm, but if it doesn't it can be made up for with a gearing change.

 

Part one of the first link says “Horsepower Vs. Torque - Part 1: There is a long-time discussion among racers concerning the question of which is "better"; horsepower or torque. Well, the short answer is that you need both. But horsepower is what you're after if what you want is to accelerate quickly.” It goes on to say almost exactly the same thing as my last example.

I love a good debate

 

Yeah, after reading the posts, MustangGt221 has the right idea, it's just that this is a touchy subject when trying to explain it in simple terms.
In that 302 vs 460 case, all things egual, except the motor, I'm pretty sure the 460 would come out on top. the 302 is much lighter, but at 500HP itll be making most of it's peak torque, and HP at a much higher RPM then the 460. The 460 will much more torque at a lower RPM, and thatll bring it up to speed a little faster than the 302. Rememeber this is if all things are equal, except the engines.

 

New on this one.
It takes torgue to get an object moving (ie 10000lbs trailer)
It then take horsepower to sustain that movement?

 

This example? It might not go far or fast, but it accelerates to it's top speed very quickly.

In the link I posted they don't elaborate much on why HP allows you to accelerate more quickly until later in the discussion. Here's a quick explanation why. Hopefully the visual aids will help.

Based on the argument that both of the engines below were installed in identical vehicles (weight, gearing, body, etc.), you guys are saying that the bottom graph will accelerate faster because it has more power. Before I go much further I'll let you know that the top graph is my truck and the bottom graph is a friend's SVT Focus. My truck has run the 1/4 in 16.8 at about 4200 lbs and the Focus runs about 16.3 at about 3000 lbs. With so much less weight and slightly more power, shouldn't the Focus destroy the truck in a drag race? It doesn't because there isn't much torque compared to the truck engine. At its power peak (3100 rpm), the truck engine is making about 240 ft-lbs of torque. Running through 4th gear (direct drive) and a 3.08 rear axle there will be 240x3.08 = 740 ft-lbs of torque at the rear wheels while making 145 hp. The Focus makes peak power at 6600 rpm, where there is only 120 ft-lbs of torque. If it were equipped with 3.08 gears there would be a whopping 370 ft-lbs going to the wheels. Hardly enough to move the car. If the Focus is regeared to so that its power peak fall at the same speed at the truck engine it would need 2.13 times more gear, or a 6.56 axle ratio. Then when at its power peak it would be sending 790 ft-lbs to the wheels. That's 50 more than the larger engine with more torque and that's why higher HP allows greater acceleration. It's because it allows more torque to be available.

 

I could be wrong on this, but I’m pretty sure it does not make sense to multiply the torque number from a chassis dyno by the gear ratio. Since the original reading was measured at the wheel/dyno interface it already has the gear ratio accounted for. Change your differential up or down and the measured torque goes up and down.

I can see where you would need to multiply through to account for gearing if the number was brake torque and you were trying to come up with a net result.

 

LOL
ok, man, listen to what is actually being said. NO ONE said that HP is the only reason a person can get fast acceleration. In fact just the opposite. Go and read the posts over, and post back, tell us what your conclusion is then. If you have to, forget that MustangGT221 was the one posting. Might make it better for you?
And second, 240*3.08=a joke....Those numbers are at the rear wheels, meaning-numbers shown=numbers you get....or as close as that dyno allowed.
I'm sorry if I come across as a bit of an ---- to you, but you should re-read your last post...it really makes you look like someone who needs to study this a little more.

 

Actually most of the major points made in this thread are very similar. Each person just describes it differently.

Torque in its simplest description is a force applied to change the current state of your truck. If your truck is stopped, torque is the force that makes it move. If you are driving down the road at 55, torque is the force that changes the speed and allows you to accelerate or decelerate.

Horsepower, as mentioned several times, is simply a mathematical formula expressing the rate in which the torque is applied. The quicker (RPM) you can apply/reapply the torque the more work can be done (HP). One of the websites cited had a great analogy using paychecks to represent torque, pay frequency to represent RPM and buying power to represent horsepower.

400 foot-pounds of torque applied by a man with a breaker bar at the rate of two revolutions per minute (0.15 HP) will propel the truck through the quarter-mile in a day or so. The 400 foot-pounds of torque applied at 5000 revolutions per minute in a stock lighting (380 HP) will take the truck trough the same quarter mile in 13.8 seconds.

The available torque is the same. The rate (horse power) is significantly different.

 

The numbers given by a chassis dyno are flywheel numbers corrected for drivetrain losses, they are not what the rear wheels are actually doing. I'm not the one who needs to go back and review the material. The dyno knows how fast the roller is spinning, how fast it is accelerating and how fast the engine is spinning. From that information it calculates the corrected flywheel number, which is shown on the chart. You might be able to figure it out on the Dynojet website, I think they have a "How it Works" section.

I have reread the whole thread 3 times. Like I said, the first post was good and it went downhill from there. Horsepower does not in any way equal acceleration, and even if it did you get more hp by increasing torque. The only thing power does is allow you to operate at higher speeds.

I said previously that 1000 hp is useless if there is not torque behind it, and I stand behind that statement 100%. A 1000 hp engine that makes 100 ft-lbs of torque will not go anywhere unless it is geared to the moon. Gearing increases torque in proportion to the amount it reduces rpm.

 

It would be helpful if we could leave gearing out of this. I thought I had it figured out until this was introduced. How about for simplicity we use a ski boat engine - direct drive from the engine to the prop - no trans, no diff, no gears. If we created an engine that produced 500HP and 100 lbs of torque someone please explain to me what this boat is good for, towing or speed - along with why. My understanding is it is made for speed because a tugboat engine may be 100HP and 500lbs of torque. Obviously tugboats move very slowly, even with that massive torque.

I've gone back and re-read this but am now confused (again ) because gearing has been introduced.

 

Well we are getting off topic here, but I believe a chassis dyno measures torque numbers delivered to the rollers. This number incorporates the various losses in the drive train and accounts for the final drive ratio. Engine (brake) horsepower is typically estimated at 18% higher than rear wheel horsepower. I have heard of some dyno software attempting to measure the spin-down and generate an estimated Break HP but from what I gather this is considered pretty inaccurate and that number is not used frequently.

If you can point me to an example I would be glad to read it. I checked the Dynojet site but did not see a “how it works section”.

You have my full agreement that gearing increases/decreases torque in proportion to the amount it reduces/increases rpm so we can ignore gearing move back to the original subject.

 

This thread is hilarious. What we have here is a whole bunch of people trying to explain a concept to one another that they themselves don't understand. I have never seen a thread on this forum that was so full of misleading, misinterpreted, and just plain wrong information.

Totally wrong. Torque is force. Some examples of force are gravity and magnetic attraction. Both of work fine without some sort of rotation being involved.

The space shuttle rockets put out millions and millions of horsepower. Again, there is no rotation involved. And therefore no torque. If you think there is, where can I put a device on a space shuttle engine that will allow me to measure torque?

Torque is a pretty easy concept to grasp. Horsepower is much, much more advanced. It is an abstract concept, so it's difficult for most people to comprehend. I know that I haven't seen a single person on here who fully understands it.

 

I stand corrected - this guy understands horsepower. These are great analogies.

 

Which is why some of us are on here trying to weed through this to understand it

I do have to disagree with you on one point though. Mustang wrote:
Torque does not move anything unless it has RPM...put the two together and you've got movement.

You responded:
"Totally wrong. Torque is force. Some examples of force are gravity and magnetic attraction. Both of work fine without some sort of rotation being involved."

Torque IS a measurement of movement (rotation) by definition. "The force applied to a lever, multiplied by its distance from the lever's fulcrum, is the torque." In the case of anything related to torque some movement is required, in an engine that movement is the speed on the shaft, or RPMs. An engine at rest has 0 torque because it has 0 RPMs. Gravity and Magnetism do not need rotation because they are the force measures of other things. I'm not going to get into explaining gravity or EM here.

 

Torque is the force only. Go back to my example of the 200-pound guy and the 2-foot breaker bar. This time imagine that the truck is in gear and the brakes are locked down so that it requires more than the 400 foot-pounds to make it move. The guy can sit on the bar and exert 400 foot-pounds of force all day long. The force is there - it does not require movement to exist. Rotation (if any) is a result of the force being applied.

Hey in case you guy were wondering: I’m qualified to discuss these technical topics because I stayed at a Holiday Inn Express last summer….

Sorry I could not help myself.