Horsepower vs Torque

[GuzziMoto]

I was on another forum, a much less exciting forum full of Honda Kool-aid drinkers, and the topic of horsepower vs torque came up. There was a side aspect of that, what is the best rpm to shift at. I have little faith that the topic will yield very exciting conversation there, but I expect that the same topic here may yield better results. And I enjoy discussing technical things like that.

I find that a fair number of people don't fully understand the relationship between horsepower and torque. Some people say things like "torque is really what is important", or "I would rather have a motor with lots of torque than one with lots of horsepower". They often don't pay attention to WHERE the torque is made, at what rpm, and what impact that has on horsepower and how fast it will then go.

An example, they posted a chart comparing the horsepower and torque between a Honda NC700 and an Suzuki SV650. The Honda only made about 2 lb-ft of torque less than the SV, but because of the difference in rpm where the torque is made the SV killed the Honda on horsepower, making something to the effect of 40% more horsepower.

1/4 mile times I found show the SV kills the NC in spite of the NC having more displacement.

I am sure the NC is easier to ride around town, as is the CTX that shares the motor and drive train. And it does get better gas mileage (by an equal chunk more) in spite of being heavier.

I just find it interesting how the dynamics of torque, horsepower, and rpm, work

 

[czakky]

I've heard dyno guys say that when a torque curve isn't flat that somehow it tells them that there is room for tuning thus more HP is available.... that really messes me up. I have also been told that basically HP is torque multiplied by RPM (over simplified of course).

Also why do drag strip guys always say that it is about how you use the torque to get your 1/4 mile times lower.

Sorry I'm no help, just have more questions.

[LowRyter]

Torque = 5252 X Horsepower / RPM

 

Horsepower = Torque X RPM / 5252

 

essentially HP is power measured over 5252 rpm and TQ is power measured below 5252 rpm.....  the values are equal at 5252 rpm

[Lucky Phil]

Torque is force and horsepower is the RATE at which the torque or force is delivered.

So 2 men pushing say an identical concrete block ( ignoring friction etc ) One can push it twice as fast as the other. Both produce the same force but one has twice the power of the other

Ciao

[Scud]

I didn't know there was Honda Kool-Aid. I assume it's red? 

 

The way torque and horsepower get to the street are, of course, also affected by gearing. For shaft-drive bikes, this is generally fixed. But it can be altered on chain-drive bikes; changing the sprocket sizes has a big affect on how much torque we perceive - or at least when we perceive it.

 

Building on Phil's explanation - this is also why two vehicles with the same horsepower might be able to tow different loads. A diesel truck with 300HP is going have a lot more torque (and at lower RPMs) than a sports car with 300HP. The truck generates more force and can pull the trailer.

 

So back to bikes - I think this is why we hear references to Guzzis being tractors or freight trains. And I like it. I like the brutish power on a steep ascent. I think I am talking myself into a night-time canyon raid... 

[GuzziMoto]

Well, I like Lucky Phils explanation. That is pretty much the way I think of it as well.

As to a truck making 300 hp ( or more likely 300 lb/ft of torque) vs a car making the same amount of power, I think that is more a function of where the torque is in the rpm range and the area under the curve. A broader torque curve can be a good thing in a street car, and even more so in a tow vehicle.

 

Here is a link to a great article from Hot Rod Magazine that talks about the differences.

One of the best parts of that article is that it highlights how people with a lot of understanding on the subject still dis-agree about the difference between HP and TQ.

 

I don't think of the Guzzi motor as an overly torquey motor. It makes good torque, but compare to the Buell X1 I used to own it is not that torquey. Most on here seem to think of the Guzzi motor as a rev'er, and again, compared to previous bikes I have own it is not that either. I think it is very much a mid range motor, with an almost electric motor abundance of power at 5 grand.

 

And yes, Honda Kool-Aid is red.

 

Edit; forgot the link.

http://www.hotrod.com/how-to/engine/hrdp-0401-torque-horsepower-guide/

[Scud]

Here are a couple links to charts for two Fords: a 5.0L Gas Mustang and a 6.7L Diesel Truck.  

 

They both make similar peak HP (370 for Mustang, 390 for Truck). The Mustang peak torque is 352 ft/lbs. The truck makes 735 ft/lbs of torque with a remarkably flat curve. 

 

The diesel only goes up to 3700 RPM, while the Mustang goes much higher - and you can see the HP/TQ intersection at 5252RPM. Note that the HP and TQ curves intersect on the truck's chart at 3000 RPM, but that's because the HP and TQ scales are not the same - if the scales were the same, the HP curve would be far below the TQ curve the whole time.

[LowRyter]

or said another way...all things equal,  a 2.0 liter engine will give you the same power at 6k rpms that a 4.0 liter engine will give at 3k.  One doing it with horsepower and the other with torque.  

[LowRyter]

Well, I like Lucky Phils explanation. That is pretty much the way I think of it as well.

As to a truck making 300 hp ( or more likely 300 lb/ft of torque) vs a car making the same amount of power, I think that is more a function of where the torque is in the rpm range and the area under the curve. A broader torque curve can be a good thing in a street car, and even more so in a tow vehicle.

 

Here is a link to a great article from Hot Rod Magazine that talks about the differences.

One of the best parts of that article is that it highlights how people with a lot of understanding on the subject still dis-agree about the difference between HP and TQ.

 

I don't think of the Guzzi motor as an overly torquey motor. It makes good torque, but compare to the Buell X1 I used to own it is not that torquey. Most on here seem to think of the Guzzi motor as a rev'er, and again, compared to previous bikes I have own it is not that either. I think it is very much a mid range motor, with an almost electric motor abundance of power at 5 grand.

 

And yes, Honda Kool-Aid is red.

I agree with you.  A Guzzi motor is a revver not a puller.  The sweet spot is over 4k rpms.  My EV doesn't go into 5th gear until 80 mph.  

 

I think twins have a limited power range compared to my 4 cyl bike.  You can give a twin top end power, mid range or bottom end torque but you can only do one.  My 4 cyl bike can do all or at least two of three.  

[GuzziMoto]

I think perhaps what makes the Guzzi motor seem like it is a rev'er is that within its allowable rpm range it makes it power more so in the upper half of that rpm range. But on the other side of that is that to me a motorcycle engine that only revs to 8 grand is never a true rev'er. I have ridden/raced Ducati's that rev'ed past 10 grand, some as high as 12 or 13 grand. That is a big twin motor that revs out. I know it is apples to oranges, just trying to explain where I am coming from.

 

That 6.7 Powerstroke chart would be more fun to look at if they used the same scale for HP and TQ. That really highlights the difference between HP and TQ.

[GuzziMoto]

or said another way...all things equal,  a 2.0 liter engine will give you the same power at 6k rpms that a 4.0 liter engine will give at 3k.  One doing it with horsepower and the other with torque.  

That is a cool way to think about it.

 

We used to have a similar view between two strokes and four strokes.

[docc]

One of the great things about this topic is how it invites comparisons, like between two and four strokes, Guzzi and Honda, dynos and seat-of-the-pants.

 

My little Honda GB500 is a good example compared to the "classic" British singles of the same displacement. With four valves and typical Honda engineering, the GB is best "on the cam" at some higher rpm than the lower rpm "power" of the two-valve classics. True to the Honda idiom, it is not at all about "grunt."

 

I love it just the same, but am probably more of a "grunt" rider/driver . . .

 

Oh, and that Honda Kool-Aid? Red indeed. " Ride Red ! "

[dangerous]

easy... give me torque over power any day, look at the Guzzi, shit if a torque bike gets the start on a high HP bike and it should... a decent rider should keep that lead

[PDoz]

easy... give me torque over power any day, look at the Guzzi, shit if a torque bike gets the start on a high HP bike and it should... a decent rider should keep that lead

Not really. The guzzi has a fairly flat torque curve - sitting between 50-60 NM from 3k all the way to 8 K , hence the relatively linear increase in power. So if you take a higher revving bike that also has a flat torque curve of 50-60 NM , they'd be neck and neck right up until the guzzi hit 8K , then the HRB would start pulling away AND STAY IN A HIGHER HP RANGE with every gearchange - so it'd keep pulling away.

[dangerous]

well on paper is one thing imo often reality another, ie on the track is different to around the hills, torque is going to squrt you from corner to corner the high HP bike will still be trying to wind up