Power vs torque

[Guest mightymax]

I cannot figure this out maybe some fellow forum members can help me out....

What influences power and torque?

1.)For example running increases stamina/endurance while wieght lifting increases strength for human...

For cars what mods increase power or torque???

OR

2.)Is it dependent on the nature and characteristics of the ECU?e.g.power fc vs possumlink

OR

3.)Can the tuner trade off power and torque?

Foe example:car A: 100kw(power) and 50nm(torque)

car B: 50kw and 100nm(torque)

Which car would have a advantage on a flat surface and a steep slope?

[Warpspeed]

Torque is a twisting force, just the same as you would apply with a spanner to do up a nut.

Fifty foot pounds of torque is like a fifty pound weight on the end of a one foot spanner. Or five pounds of force on the end of a ten foot spanner.

This is simply a force pushing, pulling or twisting on something.

Power is the rate of work being done, or force times speed. If you do something twice as fast, it requires twice the power.

So, power equals torque times speed. expressed Ft-lb x RPM.

A long time ago a guy calld James Watt got himself a genuine hairy horse, and did some measurements to see how much weight his horse could lift or drag in a certain time.

He decided that his horse could lift a 550 pound weight one foot each second, and this has now become the standard unit of horsepower. True !

We now have the formula , Horsepower = Ft-lb x RPM / 5252

Getting back to internal combustion engines, torque is twisting force only. The main factor deciding torque for a non supercharged engine, is the size of the engine, that is the bore, stroke, and number of cylinders.

Power for a heat engine is the rate at which air and fuel can be burnt in a given time. So power has more to do with airflow through the engine than the size of the engine.

I small high reving motorcycle engine can make a lot of power because it can spin so fast, but will not have a lot of torque because it is small.

A huge truck engine will make a lot of torque because it is big. But because it cannot spin fast the power will be relatively low.

A gearbox can reduce the speed of a shaft and increase the torque at the same time, but the power remains almost exactly the same.

So a one hundred horsepower motorcycle engine fed through a reduction gearbox can produce the same torque and RPM as you would get straight from the one hundred horsepower truck engine.

Does that help ?

[hungry6]

arhhh u got it all wrong!!!

torque is what moves your car down the road, and power is what moves it out of the show room!!!!

[Warpspeed]

Too true.

A lot of guys on this forum brag about what power they are making at the wheels, but if you ask them what torque they have, you usually get a totally blank look.

[Guest mightymax]

Thanks guys so the force that pulls u back when u accelerate is due to power or torque?

[GTR King]

Fact : Torque rules the street, Horse Power rules the strip.

Simple aint it.

[Warpspeed]

Torque is the twisting force that turns the wheels and accelerates the car. Sometimes called tractive effort.

Power is tractive effort times speed.

GTR king is pretty right in his statement. Torque = acceleration, power = speed.

[matlowth]

Okay - easiest way to get more torque is to increase capacity. Now how do you do that on a motor? Increase the boost.

If you want more power, you play with your mixtures, let the motor breathe better, etc etc...

matt

[b2barker]

Power=Torque*RPM*a constant

If you make good torque at high RPM you make good power, and can take better advantage of gearing.

My last car was a Civic VTiR, which had bugger all torque, but peak torque was over 6000RPM, leading to peak power of 118kw at 7200rpm.

I am driving a 3L diesel lowlux hire car at the moment, which has heaps of low torque but this drops off well below the 4500 redline:uh-huh: . It can accel up a steep hill in fourth at 1700 rpm, but would do a 0-100 in 15 seconds.

Power is all about where your torque is in the RPM range.

As an aside dynos don't measure power they measure torque and calculate power from this and tyre rpm or tacho rpm.

[sparc]

http://www.autospeed.com/A_0755/page1.html

[GTR King]

Hey Sparc thats me m8`s Dave Adams car, That thing is a Torque MONSTER :]

Runs 9 seconds all day , think its injected with NOS :]

[whatsisname]

Originally posted by b2barker

As an aside dynos don't measure power they measure torque and calculate power from this and tyre rpm or tacho rpm.

Exactly! I'm glad someone pointed this out.

[MegaGTS4]

In the future we all might end up driving cars that have a engine that has a capacity of 2cc and does 1000000 rpm and through a reduction gearbox creates enough torque to drive a car!

Wonder what it would sound like at 1000000 rpm though!!

MEGA

[JimX]

Originally posted by Warpspeed

Torque = acceleration, power = speed.

You got that around the wrong way. With a lot of power you can gear it down for very quick acceleration, but without the torque your top speed will suffer. So on a simplistic basis, you could say that power=acceleration and torque=top speed. Of course gearing affects this, but that's the basics.

A lot of people talk about fast drag cars which have a lot of torque, but these also have a shitload of power. Take a look at a Mack truck. It has mammoth amounts of torque but not too much power (on a relative scale). They accelerate like slugs but can still get up to well beyond highway speeds. You're not going to run a 9s quarter mile on a normal truck engine no matter what your gearing is.

[Warpspeed]

Well jim your half right.

I still say torque = acceleration. Which gear gives the greatest rate of acceleration, first gear or top gear ? Why ?

Tractive effort is what accelerates the vehicle.

Now if you want to talk about the fastest way to cover a certain distance, that is different thing altogether. What you need is the HIGHEST AVERAGE SPEED to cover a given distance in the shortest possible time.

For this you need high power, because time becomes an important part of the problem. So yes, high power is the most significant factor in getting a low ET, or high terminal speed.

So power = speed.

[JimX]

Warpspeed,

Torque is the only thing acting on your wheels, so you're splitting hairs here. The simple reason why your car accelerates slower in a taller gear is because you are reducing the power to your wheels. Have you ever seen a dyno chart? The torque curve stays fairly flat all the way along, but the power goes up with the speed and eventually tapers off. If what you were saying was true it'd be the other way around.

What I'm saying is if you have a high powered engine with not a lot of torque, you can compensate for a lack of torque with gearing, which will improve your acceleration but won't improve your top speed unless you had a really short ratio, and you lengthen it to the point of finding the engine's torque limits.

Once you're past the threshold of your maximum torque, no amount of gearing will increase your top speed. Even if you're not redlining, eventually there will be a gear ratio that will limit the vehicle's top speed. It is a lack of torque here that's stopping you going any faster, not power. Therefore you could say that the amount of torque governs your top speed.

Your example actually illustrates this. You're talking about a high terminal speed. You're using power to accelerate to this speed, not maintain it. So yes, you need a high powered engine to get to that point as quickly as possible, but the actual speed you can reach is a reflection of your torque.

Even most normal cars have enough power and torque to keep accelerating way beyond the standing quarter mile so it's not a very good example. I have ridden 250cc motorcycles that can accelerate quite quickly to about 130kph, but the top speed is like 150 and the acceleration from 130-150 is much less than from 0-130. When at 150 in top gear, the engine is way below redline but it just won't go any faster even if you drop it back a gear. These bikes have high powered engines (40hp or so) but very little torque, which is why they can't go any faster.

I maintain that I am entirely correct, and even your example proves this. If I'm half correct then that means you're also half correct, which means we're both correct? That doesn't make any sense

[Warpspeed]

I have read through what you said a few times, and cannot disagree, I think we are looking at the same problem from a different angle.

For instance you say when you go up a gear the power to the wheels drops because engine RPM drop. Quite true, I had never really thought of it quite like that.

And as you say if the torque curve is (almost) flat, then the torque at the wheels will drop because the reduction ratio through the gearbox is less in the higher gear. It is really saying the same thing but looking at it from a different perspective.

When gearing a competition car for maximum performance it is the power curve that is most important. Gearchange points should be either side of the maximum peak power point so maximum area through the power curve can be used in each gear.

The torque multiplication through the gearbox will be maximum under these conditions in each gear, giving greatest acceleration.

If you only rev it to the engine torque peak at the same road speed, you will be in a much higher gear, and actual acceleration will be less.

[GTR King]

Warp u sumed it up with this statement, I was wondering who would get it right first 10 points.

"Gearchange points should be either side of the maximum peak power point so maximum area through the power curve can be used in each gear. "

totaly true. thats how i geared my car

my car only uses a 1500 rpm rev range

[Guest (_W.4.S.P._)]

this is a great topic ,,

For cars what mods increase power or torque??? c'n'paste

so torque will get increased by a longer stroking engine or by a larger cubic capacity

and

power will increase by getting more revolutions per minute onto the rear wheels ?( motor, g box , diff ? )

umm ,, side Q? ... what stops a cummins turbo deisel from reving to 9000 per min? roller bearing the thing and put it in a gemini and bombs away ????