Power vs torque

[Bignige]

I can differentiate them in my head but buggered if I can put it into words.

How does one describe them?

[comm_SS_V8]

Power Definition:

1. A measure of work being done.
2. The rate at which work is being done. In mechanics, power is measured as torque times speed and expressed in units such as horsepower or watts.

Torque Definition:

1. The measure of a force-producing tension and rotation around an axis.
2. A twisting force which may or may not result in motion.

>> Edited by comm_SS_V8 on Monday 24th October 22:45

[ringram]

HP = Torque * RPM / 5,252

So if you get enough RPM you are going to have good HP. Its torque that accelerates and wins the traffic light races. You use gearing to put the car into the power band. HP is the rate at which torque is applied.

Basically torque rules.

[stevieturbo]

Or another way I once read....

HP determines how fast you hit the wall when you crash.
Torque determines how many walls you keep knocking down.

Trains, busses etc have huge torque, but relatively low power. They can pull huge loads, but at slow speeds.

Motorbikes make relatively huge amounts of power, but no torque. So they can go fast, but they dont ahve any torque to pull any weight..

[sid447]

http://vettenet.org/torquehp.html

http://impulsengine.com/performance/m

www.car-videos.com/articles/horsepower_torque.asp

[stu harris]

Power for show , torque for go

[P47ThBolt]

Why is the merc c320 as fast as the 5.5AMG version 50 - 75 probably where most people do their overtaking? I guess it is down to how you measure performance.

It is also about how wide or narrow the torque and or the power band is i.e. the delivery/what is on tap and for how long. You often hear about a nice straight torque curve. The point is smaller capacity TD's )and TD's in general in the past)like the golf offer big torque in a narrow band so the accelerative affect is strong but brief before you have to change gear again.

Big grunty V8 =strong accelerative affect maintained over a long period of time. That is why our cars feel liek they will just keep on accelerating.

Once on the move torque rules if you want big mid range grunt. That is what makes the rally bred turbo charged Jap weapons or S/C AMG's Astons, HSV's so quick a good mix of power and big torque - in essence getting a smaller and lighter engine to reproduce power and torque characteristics of a NA V6/V8.

Also the HSV/Holden beasties are big heavy cars.. you need big torque to get them moving quickly ask an RX8/Civic Type R driver why lack of big torque is not good.. you need to drive everywhere with your hair on fire and needing ear plugs...to access the largely power driven performance. Fine for a race track bloody wearing eveyday.

If you use 0-60 and 0-100 as performance benchmarks that will drive you a certain way to set your car up. Just don't be surpised in the 'realworld' when a car set up with good mid range gets the better of/closer to you than you expect.

0 - 100 is a better indicator of strong on going acceleration through the gears but look at Autocar 30 - 70 times at the rear more indicative or real world oomph ( cars with good 30 -70 tend to have good 0-100 as well).

Wait for the new BMW 335d. Might be a BMW and diesel but it will go like hell. The 535d 30 - 70 is only a second behind a stock VXR and I bet the gap does not get any bigger until the VXR is up into 3 figs.

Before eevryone starts on about not same cars its BMW etc etc. this is just an illustrative measure of how torque affects peformance when set up right without the same matching big power.

I am sure the experts will give a better description of the right mix of power and torque and curve shapes etc.

In essence big low down torque that is availabel right through teh rev range with big top end power on top. I understand that is the best way to go for maximum oomph on the road.

[cptsideways]

The torque is amount the engine twists in the engine mounts, this changes as the revs build up. Easy to see when a cars on the dyno. ;0


BHP is whats produced at the other end and is that much twist multiplied by the revs, more at more revs is more bhp etc.

[ringram]

Depends on the torque curves. You want area under the curve.
Ill take the one with the most torque over the widest RPM range.

Also small desiels dont rev high, civic type R revs well high so maintains high torque over a longer period.