Torque vs. HP

[hoihtah]

i'd say... scsifreek has it about right.... so i won't go into it much.

i drive an integra gs-r which has good amount of hp... but not enough torque.
so... when do i notice this? when i have lots of heavy people in the car.

with just me in the car... i can make the car fly...
but with 4 people in it... it moves like a civic.

in real life... you want them both.
if you want a neck jerking acceleration... make sure you have lots of torque.

think about motorcycle engines...
you never see a motorcycle tow a boat or anything else for that matter...
even though it's got plenty of hp.

that's not only because of it's lack of third or fourth wheel.
it also has to do with the lack of torque. it just wont' happen.

 

[Zenmervolt]

<< Torque <---- If you step on the gas and see your passengers wave their head back thats torque. it always makes me laugh when I see everyone in the car wave their heads back once i step on the gas.


HP<----- While you're going up a hill and you step on the gas it keeps on accelerating now thats when HP plays a large part. You won't see Civics nor Corrolas accelerate much going up the Hill do you? and I aint talking about small hills but more like 35 degree to 45 degree hills.


--Scsi >>

Acceleration, uphill or on level ground, is an action from Torque. Hill climbing is a very good indication of why torque is important. Diesels typically have a high torque/horsepower raion (ie lots of torque, not as much horsepower). An engine with a lot of horsepower but almost no torque will not be good at climbing hills or carrying loads (and hill climbing is really an artificial creation of a high load). This is why trucks and work vans typically have high torque engines, for example, the Ford 5.4 litre V8 in my friend's E-250 has 260 horsepower and 350 lb-ft of torque because in a hauling application torque is more important.

ZV

EDIT: To simplify (perhaps overly), torque is a measure of the ability of the engine to change its velocity. The greater the ability of the engine to change its velocity, the less noticable heavy loads on the vehicle become. Horsepower is a derivative of torque and engine speed.

 

[NonTechGuy]

have you actually watched truck races on TV? those semis? those things FLY without a trailor on the back!

it's really entertaining to watch

 

[audiophan]

more torque = quicker takeoff
more hp = faster top speed

 

[Kntx]

As a few people have already pointed out, Horsepower is simply a function of torque and RPM. It cannot be directly measured.

HP = TORQUE x RPM / 5252

All of this BS, like "Torque is what makes your car go up hills" is crap.


<< which is to say if you increase torque at a given RPM you increase HP >>

<< That is incoorect. When VW had Porsche tune their VR6 for the Eurovan camper torque was increased but HP dropped >

You are the one who is incorrect. Porsche may have increased the PEAK torque, but if HP dropped that means it was making LESS torque at the POWER peak. Take a look at a HP/TORQUE graph someday...

In the end HORSEPOWER is the BE ALL AND END ALL of engine performance measurement.

WHY??? BECAUSE CARS HAVE GEARS!!!!

The only time torque is important is in first gear. This is beacause you are forced to start from a low engine speed. And therefore will have low HORSEPOWER if you have low TORQUE.

At all other speeds, thru gearing you can keep your car as close to the power peak as possible.

TORQUE AND RPM CAN BE CHANGED BY GEARS BUT HORSEPOWER ALWAYS REMAINS THE SAME NO MATTER WHERE YOU MEASURE IT.

Example. Let's say at your CRANK you are making 200 lb/ft at 6000RPM, you are now making ~230 HP.

but at the wheels, after your car has been geared down 10:1.....

your wheels are spinning at 600RPM, still 230 HP, but.... you are putting down ~2010 lb/ft of torque.

get it????

 

[iamwiz82]

This website has a GREAT explanation

 

[Zenmervolt]

<<In the end HORSEPOWER is the BE ALL AND END ALL of engine performance measurement.

WHY??? BECAUSE CARS HAVE GEARS!!!!

The only time torque is important is in first gear. This is beacause you are forced to start from a low engine speed. And therefore will have low HORSEPOWER if you have low TORQUE.

At all other speeds, thru gearing you can keep your car as close to the power peak as possible.

TORQUE AND RPM CAN BE CHANGED BY GEARS BUT HORSEPOWER ALWAYS REMAINS THE SAME NO MATTER WHERE YOU MEASURE IT.

Example. Let's say at your CRANK you are making 200 lb/ft at 6000RPM, you are now making ~230 HP.

but at the wheels, after your car has been geared down 10:1.....

your wheels are spinning at 600RPM, still 230 HP, but.... you are putting down ~2010 lb/ft of torque.

get it????>>

You are right that torque can be multipled by gearing, however, unless you have an obscenely high number of gears torque is very important. Why do you think smaller engine that have a low torque/hp ratio have to spin at 3,000 rpm in top gear at 55 mph? Semis typically have transmissions with more than 15 gears (up to 21 in some cases) because all those gears are necessary to multiply the torque enough to move their loads and achieve sufficient cruising speed. I don't think that the average driver wants to shift through 21 gears, which is where torque comes into play. More torque means that the transmission can be designed such that the engine is only spinning at about 1,500 rpm at 55 mph. Neither horsepower nor torque is the "be all and end all", a good engine balances both torque and horsepower according to the usage demands of the vehicle and the gearing ratios used in the transmission. More torque means the ability for higher gearing, which means lower engine speeds at cruise, which means less wear on the engine and less noise in the cabin of the vehicle, all of which are good things.

ZV

 

[Kntx]

<< Why do you think smaller engine that have a low torque/hp ratio have to spin at 3,000 rpm in top gear at 55 mph? >>



It's because the smaller engine has to rev at 3000 rpm to make enough horsepower to maintain speed.



<< unless you have an obscenely high number of gears torque is very important. >>



With pretty much any 5 speed out there if you shift at the redline, you will end up within 1000 rpm of your power peak. Additionally, with the development of CVTs you can be at your power peak from 0 mph all the way up to and beyond 100 mph.



<< Semis typically have transmissions with more than 15 gears (up to 21 in some cases) >>



Don't forget the high and low range... Anyways, semis have a very narrow rev band. The gears are very close ratio.


All your points are valid. I'm just trying to cut thru all of the misinformation that's floating around. It is my opinion that horsepower is the most useful single number measure of engine performance. I think we can both agree that the best measure is an horsepower graph. If you look at the graph and notice you're making 100 HP at 2000 RPM, you must be making an awful lot of torque as well.

 

[Kntx]

I also just wanted to point out that if you're going up a hill at 30 mph; 500 lb/ft at 2000 RPM isn't going to get you up any easier than 167 lb/ft at 6000 RPM.

(both are ~190 HP)

 

[mithrandir2001]

Wow, a lot of different "opinions" here.

HP is derived from torque. It is not some independent number. That's why some have posted the "Horsepower = (Torque x RPM) / 5,252" formula.

A peak horsepower rating is somewhat meaningless because it's rather one-dimensional. The best way to determine a engine's power is to look at its torque curve. If it is flat from low to high rpms, then the engine is flexible and relatively easy to drive. I like to look at the peak torque rating and rpm. If an engine is rated 180lb-ft @1900rpm, then I know it's probably a turbo/diesel and has great off-the-line pull ability because maximum twist comes at such a low engine speed. A high-strung Honda engine may have its torque peak @5500rpm. That means that the engine feels strongest way up in its rev range...and why small-displacement DOHC engines are often revved like crazy.

And it's not just displacement that affects the shape of the torque curve. My Accord's 2.3L I-4 engine has a fairly flat torque curve for a 4-cylinder. But that's just how Honda tuned the engine. They've given it some low-end torque and given up some high-end power. But that goes with the car, being a mid-size "family" one. A Civic Si has a peaky torque curve because the engine designers expect those drivers to rev the things up frequently. Bottling all that power up at the top rev range helps keep emissions and fuel consumption down at lower revs.

For around town driving, an engine with 160hp @5200rpm, 176lb-ft @ 3400rpm will be more useful than one with 195hp @7200rpm, 154lb-ft @5400rpm...more power is available at low revs, which require less effort to reach. But enthusiast driving, the second engine is preferred because it has a higher rev limit and more interesting character.

 

[NonTechGuy]

horsepower means very little today, they started measuring it at the engine itself rather than at the rear wheel, the MOST accurate measurement of how much power your car has is torque.

cars from the 60s has LOTS of torque but didn't rate very high with horsepower, they were all low reving engines with high compression but when you mashed on the gas you would have instant power which would snap your head against the seat. torque doesn't just determine acceleration in 1 gear, its ALL gears. notice that when you switch gears your RPM will go DOWN and MOST cars of today have very low torque unless they are running at least 4k RPM.

 

[OS]

You guys are making this way too complicated. Torque is basically a measure of how fast you have to spin the engine to get good power out of it. High torque engines you don't have to rev very high to get power and vice versa.

 

[cipher00]

<< I think of it like this:

Torque gets you there, horsepower keeps you there.

'Nuff said. >>



Can someone confirm that this is reasonably accurate? (Obviously an oversimplification). Cuz I still have trouble following the more complex explanations.


Yes, it is an oversimplification, but I can confirm that this is reasonably accurate.

 

[KokomoGST]

<< HP = TORQUE x RPM / 5252 >>



Yup... like buncha folks have said, looking at the torque AND horsepower curves on a dyno are important...
but it seems there are a lot of "fishy" dyno charts in ads these days. According to the formula, no matter the circumstances, your torque and HP curves should share a point or crossover each other at exactly 5252 RPM ALWAYS!

Outersquare is being to simple... torque is the amount of twisting/rotational force put into the drive wheels of your car. Horsepower is a measure of "work" from high school physics so it is directly related to torque. Also, it means nothing if all that torque/hp isn't put to the ground... whether the drive wheels are front, rear, or both. That's why awd cars launch like rockets, they have an easier time putting power to the ground... and why rwd also rocks for launches if done right.

I definitely agree that looking at the wheel hp/torque curves along with weight are the only ways to get a good picture of a car's "power"

 

[NonTechGuy]

the torque max is not always 5200 or whatever
on cars with turbos like porches the number is higher up like 6000 and cars that are just old school (60s style) have the most torque at a lower rpm like 3500

my dad's Oldsmobile Cutlass Supreme 86 redlines at like 5k, there's no way they would set the redline below the maximum torque level
[edit]terrible grammer[/edit]

 

[Thegonagle]

Nobody said that the torque peak is always at 5252 RPM, just that the line for HP and the line for torque will always intersect at 5252 RPM. You can spot a phony torque graph within a 1/10th of a second if you know this.

It?s all in the formula. You can?t have horsepower without both torque and RPM.

 

[NonTechGuy]

so wait what does that mean?

 

[Thegonagle]

That you should have paid attention in math class.

I'll be back. I've got to find some graphs.

 

[Beau]

Bah!!! You're all wrong!

Horsepower is measured by hooking numerous teams of horses to the bumper of the car and pulling in opposite directions. You keep adding horses 'till the horses can out pull the car.
Torque is measured by hooking the powered wheels to a pully system to and placing horses on a platform that is raised by the spinning wheel on the pully system. Keep adding horses to the platform until the car can't lift it anymore, then measure the weight and height of each horse and devide by the number of horses used.

 

[Zenmervolt]

<<All your points are valid. I'm just trying to cut thru all of the misinformation that's floating around. It is my opinion that horsepower is the most useful single number measure of engine performance. I think we can both agree that the best measure is an horsepower graph. If you look at the graph and notice you're making 100 HP at 2000 RPM, you must be making an awful lot of torque as well.>>

I'd want a horsepower and torque curve, but you are certainly correct that the curve is more important than the peak value in determining the nature of an engine. If peak numbers are identical, then personal preference for the feel of an engine comes into play. I prefer a high-strung engine that runs readily to redline, but others prefer the more relaxed pull of a low-speed engine that hates revving hard. (Think Honda motorcycle vs Harley.) And I always tend to think of heavy hauling when I think of torque, which is why I pointed out the 260/350 hp/torque ratio of my friend's E-250, the horsepower isn't that far from an S2000's 240, but the torque is nearly 200 lb-ft more than the S2000's 153 lb-ft, a rather significant difference. Finally, you're absolutely right about a semi's power band, there's typically about 2,000 rpm between idle and redline so the gears are more necessary there than in a car.

ZV

 

[Thegonagle]

<< Bah!!! You're all wrong!

Horsepower is measured by hook numerous teams of horses to the bumper of the car and pulling in opposite directions. You keep adding horses 'till the horses can out pull the car.
Torque is measured by hooking the powered wheels to a pully system to and placing horses on a platform that is raised by the spinning wheel on the pully system. Keep adding horses to the platform until the car can't lift it anymore, then measure the weight and height of each horse and devide by the number of horses used. >>


Hey! You sunk my battleship! :disgust::|

J/K

 

[silverpig]

Torque and HP can also be very misleading. Take the Yamaha r6. It's got a 600 cc inline 4 cylinder engine that can produce 120 HP. I work at a golf course in the summer, and we have 4 cylinder diesel tractors that can only put out maybe 30-35 HP. The difference is, the tractor maxes out at about 3000 rpm (that's really pushing it, I don't like putting it above 1750 rpm), whereas I think the r6 redlines somewhere about 12000-14000 rpm. Now, you could say that the r6 is more powerful than this diesel tractor, and in a way, it is. The bike can get up to 150 mph no problem, while the tractor can motor along at a whole 15 mph, but we've used those tractors to haul huge fallen trees around; something that you couldn't get the r6 to do without an act of god.

 

[Zenmervolt]

<< Torque and HP can also be very misleading. Take the Yamaha r6. It's got a 600 cc inline 4 cylinder engine that can produce 120 HP. I work at a golf course in the summer, and we have 4 cylinder diesel tractors that can only put out maybe 30-35 HP. The difference is, the tractor maxes out at about 3000 rpm (that's really pushing it, I don't like putting it above 1750 rpm), whereas I think the r6 redlines somewhere about 12000-14000 rpm. Now, you could say that the r6 is more powerful than this diesel tractor, and in a way, it is. The bike can get up to 150 mph no problem, while the tractor can motor along at a whole 15 mph, but we've used those tractors to haul huge fallen trees around; something that you couldn't get the r6 to do without an act of god. >>

That has to do with the hp and torque curves (r6 makes all power at high rpm, tractor at low rpm) and transmission gearing. If the engine in the r6 was geared such that maximum speed was 15 mph, it would probably be able to haul things as well as the tractor does. Of course, 13,000 rpm at 15 mph would be rather annoying and quite detrimental to the engine since it's not going to like being around redline for a long time.

ZV

 

[Kntx]

<< I'd want a horsepower and torque curve >>



Well ya, that's what I meant anyways.

If you know one, you know the other.

 

[Beau]

<< That has to do with the hp and torque curves (r6 makes all power at high rpm, tractor at low rpm) and transmission gearing. If the engine in the r6 was geared such that maximum speed was 15 mph, it would probably be able to haul things as well as the tractor does. Of course, 13,000 rpm at 15 mph would be rather annoying and quite detrimental to the engine since it's not going to like being around redline for a long time. ZV >>




In theory, wouldn't the tractor be able to reach the 150 mph using the right gear ratio? It may take a few more gears, but all that power is going to turn the higher gears more effectively than the R6's.