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Torque vs Horsepower

K

kevinthenerd

Platinum Member
There are a million arguments going around the Internet talking about torque and horsepower. I hope this clears them up. Let me know what you think of what I just made...

Let me know if http://kevinthenerd.googlepages.com/torque_vs_hp.html works first.

If that fails, try http://www.geocities.com/k_durette/torque_vs_hp/

Also please include your background level in physics so I can know if I need to tone it up or down. Ideally I'd like to target this to the level of understanding of a novice mechanic.
 
put in simple terms torque is how much, as in how much load it can move, or in a engine the max amount it can turn on the shaft

HP is how fast, can the load can be moved, or really accellerated

torque really determines a cars top speed (along with gears)
HP is how quick it gets to it's top speed
 
Originally posted by: AdamK47
Horsepower sells the car. Torque wins the races.
Click to expand...

Tell that to those people with 200hp/400torque Diesels.

I prefer about a 50/50 match, with a looooong powerband. The Z06 engine is a nearly ideal example of this :

505HP / 470 Torque / 7000Rpm Redline = drag burner + power all over the tach = speed on the track!
 
well a late 1960's mopar 426 STREET hemi, had about 480 HP, and about 490 pounds of torque

it had more hp than that if you wanted to rev it up past redline..........................

 
The "torque vs HP" debates are more of curve shapes rather than one or the other. In general, torquey engines generate thier peak torque closer to normal driving speeds (ie: 2000-3000RPM) where as "HP" engines generate peak power higher in thier RPM band, closer to where you'd be if you were racing.

In your engine's example, there's a "sweet spot" of about 3500-5500 RPM. I've found this to be a good place for an all around daily driver. Low enough that it gets there quickly when you need it, but not so low that you end up with a castrated top end. In my truck's engine, I have a sweet spot of closer to 3000-4500RPM* (see here: http://krcperformance.net/marty_dyno/alex.jpg ) which I personally like as it's even closer to my normal driving. Now, compared to my dad's diesel (black line: http://www.kennedysdynotune.com/images/banksgraph.gif , he's got gobs or torque right at the driving RPM. But the party's over just where it starts. Which makes it a downer in the "fun to drive" and "performance" areas, but makes it great when you really do want to pull a house around. (example: http://www.rvusa.com/specbase/...AB605%7D_jayflight.jpg )

It all has to do with WHERE you want the power and when you want it. Personally, I like it right where I got it.

Now, this is where turbocharging gets interesting. It works great because the power's not there until the air gets moving, which is also it's down side. More air=more fuel. So if you don't need the power, pumping less air is good, right? Right. But when you need it, that little air compressor needs to get air to give air, so there's a bit of lag. During the 80's turbo boom lag was a constant struggle. During the 90's heat taken from the exhaust by the turbo caused emissions difficulties because the cat warmed up slower, so they fell out of use. It'll be interesting to see where this latest turbo boom goes.

*note that on the track I shift at about 5200-5300 RPM which brings me down to about 3500RPM. Note where those RPMs lie on that curve.
 
Originally posted by: Summitdrinker
put in simple terms torque is how much, as in how much load it can move, or in a engine the max amount it can turn on the shaft

HP is how fast, can the load can be moved, or really accellerated

torque really determines a cars top speed (along with gears)
HP is how quick it gets to it's top speed
Click to expand...

Wrong.
 
Originally posted by: Arkaign
Originally posted by: AdamK47
Horsepower sells the car. Torque wins the races.
Click to expand...

Tell that to those people with 200hp/400torque Diesels.

I prefer about a 50/50 match, with a looooong powerband. The Z06 engine is a nearly ideal example of this :

505HP / 470 Torque / 7000Rpm Redline = drag burner + power all over the tach = speed on the track!
Click to expand...

You wouldn't need a wide power band if the transmission was set up better, but for the current transmission, it's not so bad for cornering since you can't really pick what rpm you want accurately. It's still not torque that allows the car to accelerate, though. It's power.
 
Originally posted by: Demon-Xanth
The "torque vs HP" debates are more of curve shapes rather than one or the other. In general, torquey engines generate thier peak torque closer to normal driving speeds (ie: 2000-3000RPM) where as "HP" engines generate peak power higher in thier RPM band, closer to where you'd be if you were racing.

In your engine's example, there's a "sweet spot" of about 3500-5500 RPM. I've found this to be a good place for an all around daily driver. Low enough that it gets there quickly when you need it, but not so low that you end up with a castrated top end. In my truck's engine, I have a sweet spot of closer to 3000-4500RPM* (see here: http://krcperformance.net/marty_dyno/alex.jpg ) which I personally like as it's even closer to my normal driving. Now, compared to my dad's diesel (black line: http://www.kennedysdynotune.com/images/banksgraph.gif , he's got gobs or torque right at the driving RPM. But the party's over just where it starts. Which makes it a downer in the "fun to drive" and "performance" areas, but makes it great when you really do want to pull a house around. (example: http://www.rvusa.com/specbase/...AB605%7D_jayflight.jpg )

It all has to do with WHERE you want the power and when you want it. Personally, I like it right where I got it.

Now, this is where turbocharging gets interesting. It works great because the power's not there until the air gets moving, which is also it's down side. More air=more fuel. So if you don't need the power, pumping less air is good, right? Right. But when you need it, that little air compressor needs to get air to give air, so there's a bit of lag. During the 80's turbo boom lag was a constant struggle. During the 90's heat taken from the exhaust by the turbo caused emissions difficulties because the cat warmed up slower, so they fell out of use. It'll be interesting to see where this latest turbo boom goes.

*note that on the track I shift at about 5200-5300 RPM which brings me down to about 3500RPM. Note where those RPMs lie on that curve.
Click to expand...

If I can get an engine that stays reliable at 10000 rpm, I don't mind if I have to rev it there to make power because it's going to HAUL when it does. (Again, it's up to the transmission to get there without lag.) Otherwise, the driver shouldn't really care about how fast the engine is spinning unless they're looking for a particular sound or something else irrational like that.
 
Originally posted by: kevinthenerd
Originally posted by: Arkaign
Originally posted by: AdamK47
Horsepower sells the car. Torque wins the races.
Click to expand...

Tell that to those people with 200hp/400torque Diesels.

I prefer about a 50/50 match, with a looooong powerband. The Z06 engine is a nearly ideal example of this :

505HP / 470 Torque / 7000Rpm Redline = drag burner + power all over the tach = speed on the track!
Click to expand...

You wouldn't need a wide power band if the transmission was set up better, but for the current transmission, it's not so bad for cornering since you can't really pick what rpm you want accurately. It's still not torque that allows the car to accelerate, though. It's power.
Click to expand...

I disagree. A wider powerband reduces the need for an eleventy billion speed transmission that needs to shift every 0.5 seconds to keep the engine in the power band. On a tight and curvy road, it lets you drop it into a gear, and keep both hands on the wheel, letting the engine pull you out of the corner just before dragging you down in the next.

If someone designed a CVT that could handle high power/torque, have low drivetrain losses, is light, and is reliable, then you could concievaly program a sports car to go to peak power, and stay there until the RPM drops below or goes above the limits of the ratios.
 
Originally posted by: Summitdrinker
why am I wrong , explain

you know we all went thru this subject once before here, maybe it was a few years ago
Click to expand...

Torque doesn't determine a car's top speed whatsoever. Top speed requires the engine to fight air resistance, and that requires a certain amount of energy expenditure per time (power). If you'll look at my graphs, you'll realize that torque can be "created" out of nothing simply with a gear. It's the product of torque and engine speed that really matters (power).

(You're right on this point: horsepower does determine the acceleration of a vehicle, but more specifically it's the average horsepower throughout the power band that matters as discussed in the link.)
 
Originally posted by: kevinthenerd
If I can get an engine that stays reliable at 10000 rpm, I don't mind if I have to rev it there to make power because it's going to HAUL when it does. (Again, it's up to the transmission to get there without lag.) Otherwise, the driver shouldn't really care about how fast the engine is spinning unless they're looking for a particular sound or something else irrational like that.
Click to expand...

That's where efficiency and mechanical longevity kicks in. Those low revving diesels get 20+MPG doing thier thing. If you took a high revving 4 banger and stuck on a 3:1 gear set, you'll be worse off than just dropping in a big block gas engine with a broken fuel line.
 
Originally posted by: Demon-Xanth
If someone designed a CVT that could handle high power/torque, have low drivetrain losses, is light, and is reliable, then you could concievaly program a sports car to go to peak power, and stay there until the RPM drops below or goes above the limits of the ratios.
Click to expand...

That is precisely what I'd like to design.
 
air resistance is part of load, just like weight

torque along with optimal gearing determines top speed, when your out of torque your all done

years ago I told a young man this, he was all turbo hp is it, with a turbo 4 banger, he laughed at me at first about top speeed is torque related, but the next day he came back and said I made a good point. why?, he claimed his car would do 145 mph tops speed, but if he flipped the headlight on which ment the hidden headlights poped up, the drag slowed the car down almost 10 mph, it couldn't even hold it's speed, ya i go, not enough torque for the increased load
 
Originally posted by: Demon-Xanth
Originally posted by: kevinthenerd
If I can get an engine that stays reliable at 10000 rpm, I don't mind if I have to rev it there to make power because it's going to HAUL when it does. (Again, it's up to the transmission to get there without lag.) Otherwise, the driver shouldn't really care about how fast the engine is spinning unless they're looking for a particular sound or something else irrational like that.
Click to expand...

That's where efficiency and mechanical longevity kicks in. Those low revving diesels get 20+MPG doing thier thing. If you took a high revving 4 banger and stuck on a 3:1 gear set, you'll be worse off than just dropping in a big block gas engine with a broken fuel line.
Click to expand...

First of all, compression ignition is just naturally better at what it does. You have no losses in the throttle, and you typically run very lean, which is conducive to complete combustion. You can extract more of the heat as work with a higher expansion ratio... W=integral(pdV)

Second of all, dropping in the high-revving 4 banger would result in high losses, but the weight would be significantly less. My focus here isn't on fuel economy but on performance. Yes, it will be less efficient because you'll be wasting a lot of energy pumping and scraping oil at high speeds. This is why economy motors are designed for low-end operation. When the motor spins slowly you lose less power, and you tend to burn cleaner. You also tend to waste less with less spark advance.
 
I'm going to pull up some fun filled numbers:
'99-03 Cummins 5.9 ISB in a Ram.
245HP, 460LBft of torque. Moves around an 8000LB vehicle getting 15-20MPG (based on real numbers) Max HP is around 2500RPM
'01 Honda Prelude. 200HP, 156LBft of torque. Gets 22-27MPG (EPA) pushing around 3000LBs. Max HP is around 7000RPM

So lets take a 2.8:1 gearset and put it on the Honda. That puts us at 437LBft of torque with peak HP at 2500RPM. Not too shabby. BUT, to do that it now has to turn alot faster than it did in the Honda just to keep the vehicle moving. Afterall, that truck is going to require a lot more to push it through the air. Lets just say, about a 2.5:1 ratio. Afterall, it's a brick. That MPG will fall accordingly, putting the Honda down into the 10MPG range and having to scream like a banshee all day long. Your gearing just killed the high RPM ceiling, so your powerband isn't wider (it'll actually be narrower). And the only thing you can argue is a 500LB weight savings on a vehicle that's made to be closer to 15,000LBs.

That's a losing proposition.

Of course, when you do the reverse (putting the Cummins in the Prelude) the reality comes out just as stupid.
 
Originally posted by: Summitdrinker
air resistance is part of load, just like weight

torque along with optimal gearing determines top speed, when your out of torque your all done

years ago I told a young man this, he was all turbo hp is it, with a turbo 4 banger, he laughed at me at first about top speeed is torque related, but the next day he came back and said I made a good point. why?, he claimed his car would do 145 mph tops speed, but if he flipped the headlight on which ment the hidden headlights poped up, the drag slowed the car down almost 10 mph, it couldn't even hold it's speed, ya i go, not enough torque for the increased load
Click to expand...

His gearing didn't put him in his power band obviously. If he had a gear that was 1:1 instead of 0.9:1 (for example), he would have had that much more torque to the wheels for a given engine torque, and he would have been spinning a higher engine speed to develop the necessary power.

I think you might want to look at the link again.
 
Originally posted by: Demon-Xanth
I'm going to pull up some fun filled numbers:
'99-03 Cummins 5.9 ISB in a Ram.
245HP, 460LBft of torque. Moves around an 8000LB vehicle getting 15-20MPG (based on real numbers) Max HP is around 2500RPM
'01 Honda Prelude. 200HP, 156LBft of torque. Gets 22-27MPG (EPA) pushing around 3000LBs. Max HP is around 7000RPM

So lets take a 2.8:1 gearset and put it on the Honda. That puts us at 437LBft of torque with peak HP at 2500RPM. Not too shabby. BUT, to do that it now has to turn alot faster than it did in the Honda just to keep the vehicle moving. Afterall, that truck is going to require a lot more to push it through the air. Lets just say, about a 2.5:1 ratio. Afterall, it's a brick. That MPG will fall accordingly, putting the Honda down into the 10MPG range and having to scream like a banshee all day long. Your gearing just killed the high RPM ceiling, so your powerband isn't wider (it'll actually be narrower). And the only thing you can argue is a 500LB weight savings on a vehicle that's made to be closer to 15,000LBs.

That's a losing proposition.

Of course, when you do the reverse (putting the Cummins in the Prelude) the reality comes out just as stupid.
Click to expand...

What did that prove? Diesels are more efficient. I already said why.
 
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