let’s clarify what power and torque are, to do this we will bring some simplified examples, so, first, we will answer these questions:
What is the torque of an engine?
The driving torque, or torque, is the measure of the rotating force that the motor itself can deliver, this force is measured in Nm (newton per meter). A motor with a drive torque of 100Nm, theoretically, is able to lift a weight of 9.8Kg “hanging” from a one-meter-long arm connected to the motor shaft.
A motor with 200Nm would theoretically be able to lift a weight of 19.6Kg “hanging” from a one-meter-long arm connected to the motor shaft. This is the driving force of the engine.
What is the power of an engine?
The power of an engine, both internal combustion (gas, petrol, diesel, etc.) and electricity is the product of the engine torque multiplied by the rpm.
Simplifying the concept as much as possible, let’s say we have two motors with the same torque value, one with the ability to rotate up to 2000 rpm and one with the ability to rotate (with the same torque) up to 4000 rpm. ; the second engine, despite having the exact same strength as the first, will have practically double the power of this one.
If a backhoe motor had the same driving force (the same Nm) but could rotate up to 6000 rpm, this would have 3 times the power of the first motor.
Motor-bicycle analogy
If the difference between these two important parameters is still not clear, let’s try to make an analogy with what happens to two cyclists who travel the same climb.
The first cyclist places a weight of 10 kilograms (torque) per side on the rotating pedals and goes at a certain speed.
The second cyclist, on the same climb, puts the same force on the bicycle pedals but rides at a higher speed; the second cyclist is delivering the same torque as the first but is delivering higher power. If we introduced the third variable (time) we would introduce the concept of energy, but we are not interested in this subject of ours.
Incidence of torque and power in-car acceleration.
To understand how these two fundamental values affect the car’s acceleration parameter, for example, the classic 0-100, let’s try to imagine what happens to the engine, gearbox, and vehicle. Let’s simplify the discussion as much as possible, omitting for example the frictions involved (grazing, rolling, and aerodynamic), and let’s hypothesize to test the acceleration of a car on a perfectly flat road.
Let’s simplify again by talking about a naturally aspirated engine (not turbo) which therefore has no delays in delivering the engine torque and we begin to understand what happens.
For example, let’s say you have 2 engines capable of delivering 100Nm of torque with first gear engaged at idle speed (always on a flat road, without slopes) and fully depress the accelerator pedal. The first motor will begin to “push” the mass of the vehicle with the equivalent force of 100 Newtons per meter and the vehicle will begin to accelerate.
Going up the revs, the engine of the first vehicle (let’s assume the same as the previous example, therefore with a maximum speed of 2000 rpm) will accelerate the vehicle with a certain progression, however, once the rotation speed of 2000 rpm has been reached, it is necessary to pass at the second gear ratio otherwise there would be a stop of the acceleration and a constant speed.
Remember that the first gear of an automotive gearbox is the one that multiplies the engine torque to the maximum but reduces the speed of the wheels to the maximum. The second gear will achieve a higher speed of the wheels but with a lower force than the first gear, it goes without saying that the vehicle will also continue in the second gear in its acceleration phase but with a lower thrust.
Let’s now see the second vehicle which has an engine with the same driving force but which is able to turn at double the speed, or 4000 rpm.
This engine will be able to push the vehicle with the first gear engaged for a longer time than the previous one, exactly double, the vehicle will be able to count on the maximum thrust coming from the first gear engaged for twice the time compared to the first vehicle.
The power is much higher and this allows you to keep the most effective acceleration ratio (first gear) for longer in order to have to shift to second gear once the maximum engine speed has been reached, in this second case, 4000 rpm. minute.
Two completely different engines with the same power.
As a curiosity, let’s compare two completely different engines (but with identical maximum power) mounted on two equally different vehicles; An Iveco Cursor 13-380 and a Ferrari F355 Berlinetta.
The first engine (turbo diesel) delivers 380hp just like the Ferrari (aspirated petrol) The first delivers very high torque at low rpm, that is 1800Nm at a speed between 900 rpm and 1500 rpm.
The F355 delivers a very “low” torque but at a very high rotation speed; 360Nm at 5800 revolutions per minute. Let’s see the rotation speeds at which the two engines deliver the same power of 380hp; up to 1500 rpm the engine of the Iveco Cursor, 8200 rpm the speed of the Ferrari F355.
As you can see, Ferrari’s rpm is about 5 times higher than the Iveco truck’s rpm, but the Cursor’s torque is 5 times higher than the F355 ‘s engine torque. Here is an example of how two motors with identical power can be completely different not only from the construction point of view but also in the way of delivering the same maximum power value.
How to increase the maximum torque of the engine?
To increase the maximum torque of the diesel or petrol engine, it is necessary to introduce more fuel into the combustion chambers, this increase in fuel also requires an increase in comburent; if we talk about turbodiesel or turbo-petrol engines, the concept is quite similar.
By intervening in the electronic management (tuning) we can increase the amount of petrol or diesel injected by the injection system and increase the turbo boost pressure to bring an adequate amount of compressed air necessary to burn all the petrol or diesel.
How to increase the maximum engine power?
To increase the maximum power of the diesel or petrol engine, it is necessary that the increase in fuel and comburent not only take place at the maximum torque speed but also be extended to the higher speeds where the engine expresses the maximum power.
By intervening as before and following specific digital maps, we can manage both the maximum torque values and the maximum power values obtaining excellent performance (remember how the acceleration phase above works?).
Example of torque increase without power increase.
If by way of example, the quantity of fuel and comburent were increased only at medium-low revs, there could be an increase in torque without necessarily having an increase in maximum power.
By increasing the amount of fuel and combustion agent only at very high revs, you could have an increase in power without necessarily having a significant increase in maximum torque (generally, except in rare cases of sports engines, maximum torque is available at medium-low revs. and not at maximum rotation speeds).
By way of example and theoretically, if the engine speed were increased with the same injection and supercharging parameters, a significant increase in maximum power could be obtained without the need to increase the maximum torque value.
Conclusion
We hope that these examples may have been useful to better understand what these two values (torque and power) invade every technical data sheet and every car magazine represent.
