Torque and Horsepower - A Primer

[PlatinumZealot]

Gears allows you to change the speed of the various components of power, torque and angular. So gear is very important, but critical, gears can be changed any power you want, because the physical size of the mass, and, above all, the inertia of the rotating gears themselves.

Nope. Gearing changes the speed and torque.. but it cannot increase the power, because you can't create or destroy energy only transfer it from one form to the other.

That is why Energy generation rate or Power is very important.

[PlatinumZealot]

Raptor22/Strad... are you suggesting it doesn't take energy to move something from rest?

If it takes energy (I can assure you; any movement requires energy) and it takes a certain time (again; it does) that means you can describe the motion in terms of power just as well as you can in terms of torque.

I repeat; power and torque are simply two different ways of describing engine output. Using either power or torque to work out acceleration will get you the same answer; as long as you do the maths correctly!

In bold, is very true!! The key word description and measurement of output. In terms of rotating shaft. But I don't know about you guys I am talking about the generation of the torque and speed of that shaft. I was taking it right back to the combustion chambers.

[machin]

N_S, I simply don't see the point of what you're getting at? You can use either energy or forces to describe the motion of an object, neither is right or wrong, but energy (using power) is the simpler, more intuitive, method.

To all the "Torque brigade"; notice how the FIA only specifies a Power limit for F1 KERS? That's because there is simply no need to specify torque or rpm. The single power figure is sufficient to limit performance.

[raymondu999]

Nope. Gearing changes the speed and torque.. but it cannot increase the power, because you can't create or destroy energy only transfer it from one form to the other

Would it not onlychange torque at the axle? I'd imagine the torque figures at the engine side would still be the same.

[machin]

That's right; it only changes torque at the rear axle... but that's exactly the point... acceleration is calculated using the power OR the torque at the driven wheels. Since gearing changes the torque at the driven wheels compared to the engine flywheel it means that a single engine flywheel torque figure (without any speed info) cannot be used to assess the possible acceleration. If you know the engine speed that the torque is generated at you can select a gear ratio based on what road speed you are interested in, then you can start to make comparisons of two engines using the torque figure.

[DumHed]

think of power as a value that incorporates the torque and rpm factors in one number.

[machin]

That's it; one single figure which is unaffected by gearing, thereby making it easy and effective to compare one engine to another.

[xxChrisxx]

I think the only figure that matters is expensive fuel price. Therefore your bank balance FAR is more important than power.

[machin]

[strad]

A battery can be full of energy, but it aint gonna do any work til it's hooked up to a motor with torque to turn the wheels.

[beelsebob]

A battery can be full of energy, but it aint gonna do any work til it's hooked up to a motor with torque to turn the wheels.

/me attaches the battery to a bank of solenoids set up to generate a walking motion.

[DumHed]

A battery can be full of energy, but it aint gonna do any work til it's hooked up to a motor with torque to turn the wheels.

but a cordless drill motor can make more torque than the motor in a Tesla Roadster.

The speed will be low though, because it's not putting out much power.

Any time the car is being accelerated, power is being converted from electrical (or fuel) to motion.

You can generate torque by taping a weight to the front of the tyre, but it's not going to drive the car more than a quarter of a wheel revolution.

[strad]

WAY WAY off track

[machin]

I've added a vehicle acceleration calculator to my website, it allows you to determine the maximum possible acceleration of a typical 1000kg road car at 60mph using user defineable torque data, it takes into account the mass, aerodynamic drag, rolling resistance, drive train efficieny and inertia of all the rotating parts on the car. It automatically sets the gear ratio to achieve the highest possible acceleration at 60mph from the engine data you provide. This allows you to compare two engines from their torque characteristics; whether it be a high reving screamer or a large capacity stroker. (N.B. the program assumes there is enough grip to transmit all the motive force to the road without spinning wheels).

Power, Torque and Acceleration (Half way down the page)

Try putting in 190lbft @ 4500rpm and then 170lbft @ 6000rpm...

[Raptor22]

Raptor22/Strad... are you suggesting it doesn't take energy to move something from rest?

If it takes energy (I can assure you; any movement requires energy) and it takes a certain time (again; it does) that means you can describe the motion in terms of power just as well as you can in terms of torque.

I repeat; power and torque are simply two different ways of describing engine output. Using either power or torque to work out acceleration will get you the same answer; as long as you do the maths correctly!

Machin, we're not arguing that energy is not required. I agree that power provides a means of simple comparison, not arguement there. What we are saying is that what is measured is torque. That is converted to a power number to use as comparison.
When engineers set up a car for the race track they work the gearing to keep the engine within its maximum torque band whilst producing torque at the wheel produce power.
I have never argued that power is unimportant. In fact the formula P=2piNT/60 shows the relationship clearly.
The point that is being missed is that power on its own tells us nothing about performance. We need torque and at what RPM that T is being generated to determine where best power is produce to convert in speed (v).

Red Bull is a driving example. slow on the straight, fast through the corners, especially out of them because they have geared the drivetrain to keep the engine between it torque and power peaks for the better part of the lap.

Petrol heads become fixated on the power but that does not exist unless the energy (fuel) is converted into mechanical energy (measured as BMEP) that produces torque and RPM.

The only really effective ay to compare engine 1 to engine 2 is to measure its BrakeMEan Effective Pressure (BMEP). Thats translates to T and N which yields P for ease of comparison. But P is always presented at XXXXRPM