Torque vs BHP

[Jahee]

I've been thinking about this for a while now, i know most of this wouldnt technically be possible but just theoretically, if you had an engine with say 500BHP and 0 lb / ft of torque what would its characteristics be? and likewise what would the characteristics be for an engine with 0BHP and 500 lb / ft of torque

all responses will be appreciated

 

[Apex]

Impossible.

HP = Torque * RPM / 5252

 

[MikeMike]

Originally posted by: Apex
Impossible.

HP = Torque * RPM / 5252

thread over

 

[tfinch2]

Originally posted by: Apex
Impossible.

HP = Torque * RPM / 5252

/thread

 

[Jahee]

ok i see, i guess what im trying to establish is the differences between torque and horsepower? been confused about that for a while now?

 

[Heisenberg]

Torque is force multiplied by distance, horsepower is well...power. You could have a motor with just torque and no horsepower, but it could do no work (i.e. move a vehicle). You cannot have a motor with horsepower and no torque.

 

[MikeMike]

torque gets you up to speed
horsepower keeps you there.

 

[Apex]

Originally posted by: MIKEMIKE
torque gets you up to speed
horsepower keeps you there.

Horsepower is how fast you hit the wall, torque is how far you take the wall with you.

 

[jagec]

Horsepower's the only *real* measure. If you have the horsepower curve, you have everything. But people try to take two numbers (peak hp and peak torque) and use that as an abbreviated way of describing the performance of an engine, assuming it behaves like most gas engines do.

If an engine produces horsepower over a broad range, it seems "torquey" because you don't have to constantly shift to keep it in the powerband. If it's peaky, it feels gutless at RPM levels below peak. But proper gearing fixes this.

 

[Viperoni]

Torque is the accelerating force that pushes the car forward. The more torque a car's engine has higher up in it's revband, the more horsepower it has.

In terms of acceleration, it's best to have as much torque (or HP, whatever) as possible as high as possible in your revband to maximize acceleration as you upshift through the gears.

 

[91TTZ]

Originally posted by: Jahee
I've been thinking about this for a while now, i know most of this wouldnt technically be possible but just theoretically, if you had an engine with say 500BHP and 0 lb / ft of torque what would its characteristics be? and likewise what would the characteristics be for an engine with 0BHP and 500 lb / ft of torque

all responses will be appreciated

500 HP and 0 feet of torque is impossible, but 0 hp and 500 lb/s of torque is possible.

Let's say you had an engine with 1 lb of torque and 500 hp. Its twisting force wouldn't be much as all, but it would spin very, very fast.

 

[Jahee]

Let's say you had an engine with 1 lb of torque and 500 hp. Its twisting force wouldn't be much as all, but it would spin very, very fast.

aha, and how about if the figures were reversed? lots of torque and say 1hp

 

[91TTZ]

Originally posted by: Jahee

Let's say you had an engine with 1 lb of torque and 500 hp. Its twisting force wouldn't be much as all, but it would spin very, very fast.

aha, and how about if the figures were reversed? lots of torque and say 1hp

The engine with 1 lb of torque and 500 hp would be easy to bog down. You could simply stop it from turning when it tried to start. But if you did let it spin up, you'd break your arms off trying to stop it since it would be spinning so fast and producing so much power.

The engine with 500 lbs of torque and 1 hp would spin extremely slowly but would be almost unstoppable. But it will never rev up high. If it did, it would have more HP.


Vehicles that need to get a heavy load moving are better suited by diesel engines, since they're torquey. A tractor trailer might have only 400 hp, but it has about 1,600 lbs of torque. If you ever look at their tachometer, they have a very narrow power band. My friend had a truck, and I think from about 900-1800 rpm was its useful powerband.

 

[Jahee]

i see, ok i thought it would be something quite like that but just needed clarification thanks that was very helpful

 

[Caesar]

This thread has a pretty good explanation/discussion

 

[Zenmervolt]

Originally posted by: jagec
Horsepower's the only *real* measure. If you have the horsepower curve, you have everything. But people try to take two numbers (peak hp and peak torque) and use that as an abbreviated way of describing the performance of an engine, assuming it behaves like most gas engines do.

If an engine produces horsepower over a broad range, it seems "torquey" because you don't have to constantly shift to keep it in the powerband. If it's peaky, it feels gutless at RPM levels below peak. But proper gearing fixes this.

Actually you have it backwards. Torque can be measured directly, HP is torque applied over time.

Torque is a force, which can be measured. HP is power, which must be back-calculated from force and time. And actually, if the HP is flat over a broad range, the engine is not at all torquey. If the torque curve is flat, the HP curve just keeps going up. If the HP curve is flat, the torque curve just keeps dropping.

ZV

 

[Jahee]

thanks that link to the thread cleared it up some more, appreciated!

 

[essasin]

All you need to know is that you can really feel torque and not so much hp. Which is why there is no replacement for displacement!

 

[91TTZ]

Originally posted by: Zenmervolt

Originally posted by: jagec
Horsepower's the only *real* measure. If you have the horsepower curve, you have everything. But people try to take two numbers (peak hp and peak torque) and use that as an abbreviated way of describing the performance of an engine, assuming it behaves like most gas engines do.

If an engine produces horsepower over a broad range, it seems "torquey" because you don't have to constantly shift to keep it in the powerband. If it's peaky, it feels gutless at RPM levels below peak. But proper gearing fixes this.

Actually you have it backwards. Torque can be measured directly, HP is torque applied over time.

Torque is a force, which can be measured. HP is power, which must be back-calculated from force and time. And actually, if the HP is flat over a broad range, the engine is not at all torquey. If the torque curve is flat, the HP curve just keeps going up. If the HP curve is flat, the torque curve just keeps dropping.

ZV

Actually, a Dynojet measures horsepower directly and back-calculates torque. That's because the formula they use to measure horsepower measures the change in acceleration of a known inertia. It then takes the engine's RPM reading and back calculates the torque.

If you've ever watched a dyno where the tach hookup fell off, you'd see that the dynochart measures the HP but has no torque component.

 

[Zenmervolt]

Originally posted by: 91TTZ

Originally posted by: Zenmervolt

Originally posted by: jagec
Horsepower's the only *real* measure. If you have the horsepower curve, you have everything. But people try to take two numbers (peak hp and peak torque) and use that as an abbreviated way of describing the performance of an engine, assuming it behaves like most gas engines do.

If an engine produces horsepower over a broad range, it seems "torquey" because you don't have to constantly shift to keep it in the powerband. If it's peaky, it feels gutless at RPM levels below peak. But proper gearing fixes this.

Actually you have it backwards. Torque can be measured directly, HP is torque applied over time.

Torque is a force, which can be measured. HP is power, which must be back-calculated from force and time. And actually, if the HP is flat over a broad range, the engine is not at all torquey. If the torque curve is flat, the HP curve just keeps going up. If the HP curve is flat, the torque curve just keeps dropping.

ZV

Actually, a Dynojet measures horsepower directly and back-calculates torque. That's because the formula they use to measure horsepower measures the change in acceleration of a known inertia.

How can you directly measure something that includes time as a necessary componant?

(Answer: You can't.)

Instantaneous torque can be measured, but instantaneous HP cannot be. As you point out, a Dynojet measures a change in acceleration (i.e. it's not measuring HP) and then from that change in acceleration it back-calculates both HP and Torque.

This is similar to a speedometer. A speedometer does not actually give you an instantaneous readout of your speed, rather, in modern digital versions it measures speed over avery tiny distance (i.e. the circumference of whatever spinning thing the sensor bases its readout on), and in older mechanical versions the measurement is based on the effect of a spinning magnetic cup around a different magnet that is mounted on a spring.

ZV

 

[91TTZ]

Originally posted by: Zenmervolt
How can you directly measure something that includes time as a necessary componant?

(Answer: You can't.)

Instantaneous torque can be measured, but instantaneous HP cannot be. As you point out, a Dynojet measures a change in acceleration (i.e. it's not measuring HP) and then from that change in acceleration it back-calculates both HP and Torque.

ZV

The answer is actually easier than you think: a Dynojet doesn't give realtime results. It performs a measurement over time and then spits out the result afterwards. It uses a formula to directly solve for Power.


It's based off the simple formula:

Power = Energy/Time

The dynojet computer knows the mass of the drum and its rotational speed. Therefore it knows its energy at any given moment. The computer knows the time, and measures how fast the drum gains kinetic energy. Once it measures how fast the drum gained kinetic energy, it has solved the equation for Power.

I was involved in a lengthy discussion about this on another forum, and I finally emailed Dynojet. Here is the email:

-----Original Message-----
From: xxx yyyyy [mailto:xxxx@hotmail.com]
Sent: Wednesday, January 19, 2005 9:08 AM
To: autosales@dynojet.com
Subject: Question about the physics behind the Dynojet

This is a pretty simple question, but it's one that I've seen with many
different (and therefore many incorrect) answers.

Does the dynojet directly measure horsepower and then back-calculate torque
by taking the RPM reading into account, or does it directly measure torque,
and then calculate HP by taking the RPM reading into account?

Thanks,

xxx xxx (me)

Their reply:

The Dynojet inertia dynamometer directly measures horsepower and calculates
torque by using engine rpm. Now, the Model 224xlc with eddy current can also
use it's torque cell to directly measure torque via the torque cell.


xx yy
Dynamometer Marketing & Sales
Dynojet Research, Inc.
2191 Mendenhall Drive Suite 105
North Las Vegas, NV 89081
T(800) 992-3525
F(702) 399-1431



*Keep in mind that if you did not have a tach pickup, the dyno could still solve for Power, but it would give you no torque readout, since the equation directly measures power and not torque. It knows how fast you spun that drum, but it doesn't know your gearing or how fast your engine was turning. If the dyno directly measured your engine's torque and back-calculated horsepower, it would be unable to do that if you had no tach reading.

 

[Zenmervolt]

Originally posted by: 91TTZ
The dynojet computer knows the mass of the drum and its rotational speed. Therefore it knows its energy at any given moment.

No, it does't know the energy at any given moment, it knows the energy over a given short period of time because it can't measure instantaneous speed.

ZV

 

[jagec]

Originally posted by: Zenmervolt

Originally posted by: jagec
Horsepower's the only *real* measure. If you have the horsepower curve, you have everything. But people try to take two numbers (peak hp and peak torque) and use that as an abbreviated way of describing the performance of an engine, assuming it behaves like most gas engines do.

If an engine produces horsepower over a broad range, it seems "torquey" because you don't have to constantly shift to keep it in the powerband. If it's peaky, it feels gutless at RPM levels below peak. But proper gearing fixes this.

Actually you have it backwards. Torque can be measured directly, HP is torque applied over time.

Torque is a force, which can be measured. HP is power, which must be back-calculated from force and time. And actually, if the HP is flat over a broad range, the engine is not at all torquey. If the torque curve is flat, the HP curve just keeps going up. If the HP curve is flat, the torque curve just keeps dropping.

ZV

I said "broad", not "flat". As in, a broad peak, compared to a thin, sharp peak.

Torque is directly measured, but the number means little without the corresponding RPM value...which is a unit of 1/time, and thus your conversion to HP. Pick an engine that makes the horsepower you need, and gear it down to get your desired torque. I think the best example I read was that of a waterwheel...it has insane torque, but only turns at a few RPM or so. The horsepower rating of those things is very low. If you take an engine that produces the same horsepower, but at (say) 7000RPM, you can just gear it down to that RPM value, and you'll get the same torque. And in a much smaller package.

Originally posted by: Zenmervolt

Originally posted by: 91TTZ
The dynojet computer knows the mass of the drum and its rotational speed. Therefore it knows its energy at any given moment.

No, it does't know the energy at any given moment, it knows the energy over a given short period of time because it can't measure instantaneous speed.

ZV

The two amount to the same thing, assuming your sensors are accurate enough (ie, fast enough to register tiny changes in time). And if your sensors aren't, just make the drum heavier.

 

[lyssword]

Torque = for dump truck, helps to move heavier cars. Horspower = for sports car