Horsepower or Torque ? never quite got it.
Discussion
As I understand it torque is a measure of twisting force and horsepower is a measure of work done.
Is there a simple "seat of the pants" way to illustrate these two forces, something that would make a 10 year old understand the difference would suit me :-)
e.g. If I am at rest in my car and I accelerate. Is it torque that is accelerating the cars mass up through the gears but then horsepower overcoming the air friction once I get to a high speed.
What would be better and why ?
1. 200bhp 300ftlbs torque
2. 300bhp 200ftlbs torque
Is there a simple "seat of the pants" way to illustrate these two forces, something that would make a 10 year old understand the difference would suit me :-)
e.g. If I am at rest in my car and I accelerate. Is it torque that is accelerating the cars mass up through the gears but then horsepower overcoming the air friction once I get to a high speed.
What would be better and why ?
1. 200bhp 300ftlbs torque
2. 300bhp 200ftlbs torque
Torque for low down acceleration.
BHP for top end high speed.
There are obviously lots of other contribting factors such as car weight, aerodynamics etc, but say you had two of the same car, one with an engine with 200BHP and 300lbs/ft torque, and one with an engine with 300BHP and 200lbs/ft torque, the one with the greater amount of torque would accelerate faster from a standstill, but the one with more BHP would go quicker once it reached its optimum speed.
I'm sure other people will have their take on this, but generally speaking, this is it.
BHP for top end high speed.
There are obviously lots of other contribting factors such as car weight, aerodynamics etc, but say you had two of the same car, one with an engine with 200BHP and 300lbs/ft torque, and one with an engine with 300BHP and 200lbs/ft torque, the one with the greater amount of torque would accelerate faster from a standstill, but the one with more BHP would go quicker once it reached its optimum speed.
I'm sure other people will have their take on this, but generally speaking, this is it.
Think in terms of specific vehicles. Trucks have massive torque to give them the strength to pull lots of weight but they won't get to 60 very quickly. A motorbike has lots of BHP and will hit 60 very quickly but won't pull lots of weight behind them.
In terms of driving cars I prefer a good torque figure to a higher BHP figure. I've driven Hondas with Vtec engines which have high BHP but lowish torque. They go quickly but only once you've wound up the engine. Compare that with my BMw Z4 with it's straight six. It has lots more torque in comparison to its BHP. It pulls well from low revs in any gear and accelerates hard from higher revs. Six cylinder engines produce significantly more torque than a four cylinder engine. That's my understanding of it anyway.
In terms of driving cars I prefer a good torque figure to a higher BHP figure. I've driven Hondas with Vtec engines which have high BHP but lowish torque. They go quickly but only once you've wound up the engine. Compare that with my BMw Z4 with it's straight six. It has lots more torque in comparison to its BHP. It pulls well from low revs in any gear and accelerates hard from higher revs. Six cylinder engines produce significantly more torque than a four cylinder engine. That's my understanding of it anyway.
If you set up kind of a winch with a large spool and small spool then attach a weight on a rope to it you should be able to demonstrate the difference.
The idea is to lift the weight by the same distance in the same time using the small spool and big spool. This is horse power.
The small spool will need to be turned faster to achieve the same time but it will be easier. Low torque and high rpm.
The small spool will can be turned slower but will take more effort to do so. High torque and low rpm.
I think that is correct - I stand by to be corrected.
The idea is to lift the weight by the same distance in the same time using the small spool and big spool. This is horse power.
The small spool will need to be turned faster to achieve the same time but it will be easier. Low torque and high rpm.
The small spool will can be turned slower but will take more effort to do so. High torque and low rpm.
I think that is correct - I stand by to be corrected.
if an engine makes 100ft lbs of torque then surely the gearbox ratios, the final drive ratios and the wheel/tyre size must totally change that figure out of all recognition, different lever lengths and all that ?
Surely it must be this torque at the wheels that as a driver you will feel 99% of the time, is the only time you would experience max power when you are flat out in a gear ?
Surely it must be this torque at the wheels that as a driver you will feel 99% of the time, is the only time you would experience max power when you are flat out in a gear ?
Think of 2 piles of bricks.
The first pile is moved up the hill by a little man. He picks up a brick at a time, but runs really, really fast.
The second pile is picked up all at once by a sumo bloke in a nappy. He carries the lot, but takes an age to climb the hill with them.
They both get to the top at the same time.
The little guy is a 600cc bike engine screaming at 18000 rpm.
The sumo bloke is a big lazy V8.
The V8 can do more *work* per cycle, but the bike engine can do far more work cycles in a given time.
Torque is the instantaneous twisting force the engine can apply.
Revs is simply how many times per minute it can apply that force.
BHP is twisting force multiplied by how many times that force can be applied in a given time (eg, torque x revs)
What you really want is something that has bucket loads of torque and revs to the moon...
The first pile is moved up the hill by a little man. He picks up a brick at a time, but runs really, really fast.
The second pile is picked up all at once by a sumo bloke in a nappy. He carries the lot, but takes an age to climb the hill with them.
They both get to the top at the same time.
The little guy is a 600cc bike engine screaming at 18000 rpm.
The sumo bloke is a big lazy V8.
The V8 can do more *work* per cycle, but the bike engine can do far more work cycles in a given time.
Torque is the instantaneous twisting force the engine can apply.
Revs is simply how many times per minute it can apply that force.
BHP is twisting force multiplied by how many times that force can be applied in a given time (eg, torque x revs)
What you really want is something that has bucket loads of torque and revs to the moon...
tpivette said:
So you can have high horsepower with little torque - cos your making all your HP through revs.
But can you ever have high torque and low HP ? If you build for torque will HP take care of itself ?
But can you ever have high torque and low HP ? If you build for torque will HP take care of itself ?
To continue with the same theme, a Harley has a relatively high torque value and a pretty low amount of HP. In the case of the Harley it's to do with a high flywheel mass (it stores energy) and the cylinder layout.
Imagine a sumo wrestler (torque) and a Amir Kahn (BHP). If the Sumo can get hold of Amir he'll be able to shove him backwards in one smooth push whereas Amir would use lots of short jabs to move the Sumo wrestler back.
You generally design for torque or outright BHP although as engine size increases you'll naturally get more torque anyway.
Put your elbow on the table, arm horizontal. Now lift the heaviest weight with the hand that you possibly can, raising it slowly over a period of 10 seconds. OK.
Now double the weight. You can't lift it because your arm can't deliver any more torque.
Go back to the original weight and lift it twice in 10 seconds. Easy!
That's the difference between force (torque) and power (work done in a fixed amount of time).
Now double the weight. You can't lift it because your arm can't deliver any more torque.
Go back to the original weight and lift it twice in 10 seconds. Easy!
That's the difference between force (torque) and power (work done in a fixed amount of time).
tpivette said:
So you can have high horsepower with little torque - cos your making all your HP through revs.
But can you ever have high torque and low HP ? If you build for torque will HP take care of itself ?
But can you ever have high torque and low HP ? If you build for torque will HP take care of itself ?
Case in point, early/mid 80's big US V8s. Huge things, huge torque. 160-200bhp.
It's torque at the wheels that dictates how fast you car accelerates.
An 8000rpm petrol with 200bhp and 150lbft will be just as fast as a 4000rpm 200bhp diesel with 300lbft because the gearing will be different and the torque going to the wheels will be the same (assuming everything else is equal)
An 8000rpm petrol with 200bhp and 150lbft will be just as fast as a 4000rpm 200bhp diesel with 300lbft because the gearing will be different and the torque going to the wheels will be the same (assuming everything else is equal)
Go for torque over bhp; it's the driveable factor. It's about acceleration without having to change down to get the revs. Horsepower is how the car's top speed; realistically how often are you going to use that?
scientifically, torque is twisting motion on the propshaft via gearbox etc from the crank = acceleration. horsepower is how hard the pistons are hit by the explosion from the petrol.
scientifically, torque is twisting motion on the propshaft via gearbox etc from the crank = acceleration. horsepower is how hard the pistons are hit by the explosion from the petrol.
So - as my screen name would suggest - I have a Corvette, late 80s, only has 245Bhp but I believe they were building for torque. I like how it drives and it does pull quite well out of corners.
The newer vettes - like my mates C5 - are significantly faster accelerating and his top end is higher.
I got some figures from wikipedia, i was expecting his LS1 to have much more power and torque.....wrong, torque is about the same in both. Looking at those figures and by looking at the previous arguments then these 2 cars should accelerate similarly but the top end should be much better on the LS1. Wrong it wins everywhere, top end and acceleration. HP must be the answer, which is exactly what i didnt think !
L98= 250hp and 330-350 ft lb
LS1= 350hp and 335-365 ft lb
The newer vettes - like my mates C5 - are significantly faster accelerating and his top end is higher.
I got some figures from wikipedia, i was expecting his LS1 to have much more power and torque.....wrong, torque is about the same in both. Looking at those figures and by looking at the previous arguments then these 2 cars should accelerate similarly but the top end should be much better on the LS1. Wrong it wins everywhere, top end and acceleration. HP must be the answer, which is exactly what i didnt think !
L98= 250hp and 330-350 ft lb
LS1= 350hp and 335-365 ft lb
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