interpreting cars specifications

[rudr_p]

Well, recently I have been looking into car specs and I am unable to understand somethings. I don't understand the power and torque rating. I mean suppose a car has
Power (PS@rpm) 67PS @6200rpm
Torque (Nm@rpm) 84Nm @3500rpm

what does that mean ? will the car deliver that torque at start or at stop?
What will be the average power it will take to run the car?
67hp is that the average power or starting power or something?
basically I am confused

[Dave B.]

I like to think of torque as the ‘ability to do work’. Horsepower, however, can be thought of as ‘how quickly can the work be done’. An average Joe might be able to lift 100 pounds at the gym. A body-builder might be able to easily double that figure. Transfer this to an engine and you’ll get the idea of torque.

Horsepower, on the other hand, is a calculated figure. You arrive at it by using this formula: Horsepower = Torque x Engine RPM / 5252

The published horsepower and torque figures are usually the maximum that the engine can produce in normal conditions.

Technicians can find both these values using a machine called a dynamometer. It’s basically a braking device that loads an engine to test how much power it can make. The results from these tests are what identify the RPM points where the engine makes its most horsepower and torque. You might think that these two points would be the same, but they’re not, because although the mechanical aspects of an engine limit its torque output; the faster it can spin (RPM), the more horsepower it can make. For an example, imagine pumping up a tire with a hand pump. If you pumped only one stroke per minute, it would take a long time to pump up the tire. Pumping faster gets the job done in less time… which is basically how horsepower works.

So, a car with more torque could probably pull a heavier trailer, but a car with more horsepower would be more likely to win a race.

When does the car’s engine deliver the most torque? It depends on the engine and drive-train. An average gasoline or diesel engine will deliver maximum torque at a point usually somewhere between 1500 and 4000 RPM, depending on the design of the engine. Other power sources, like electricity or steam can deliver maximum torque just above 0 RPM. Explaining this concept is way beyond my abilities as a writer, but it’s pretty easy to research on the internet.

As to how much power it takes to run a car, well… it varies, but it’s only a fraction of the car’s maximum power output. Some factors include the amount of weight in the car, accessories like power steering and air conditioning, tire rolling resistance (both design and air pressure), the type and efficiency of the transmission and many other small differences. Some road tests used to include this data, but I haven’t seen it published in years.

I know that all this is pretty general, but maybe it will help!

[rudr_p]

Thanks @Dave B. Thank you for your elaborate explanation, it might have sounded you general but it was very helpful to me. I'll do my further reading on internet.