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Playing with power

Pratap Ravindran

I think we've got ourselves a metaphor here. Indians love cars with power. Or, more accurately, Indians like cars that they think have power. Which is all just fine but where's the metaphor? Well, there's a metaphor involved because Indians love power (o r, as clarified earlier, what they think is power) in just about everything. You don't believe me?

Try getting into an office -- any office -- without giving the security guys, or whoever the thugs who hang around at the door are, your family history, your height, weight, age and political persuasion and your retirement plans (the last assuming that you survive their interrogation and do get to retire). After all, these people have been hired to ensure that you don't walk away with a PC under each arm and not to draw up your psychographic profile -- but they don't seem to be happy with that. That's because they're into power. Power as in you're-either-at-his-feet-or-at-his-throat.

Getting back to the subject of vehicles and power, have you noticed the way people drive around in some of the wretched SUVs put out by a local truck-maker? They tear around town at high speeds, swaying and bucking all over the place, quite oblivious to the fact that they look like perfect fools trying to hotrod a contraption that, at its best, handles like blanc mange on wheels. But try telling them that...they're convinced that they've got themselves a muscle machine which , of course, makes it all right if they run down half-a-dozen elderly people in any given week. That's power...

The fact is that we don't have muscle cars in India. Not on a mass-produced basis, that is. You'll, of course, come across somebody or the other who has got himself a car that really moves. The odds are that you'll come across this guy stu ck at the same red light that you're stuck at. So much for power...

Which is why I think there's a metaphor involved. When people look for power in cars, they're basically looking for power in non-car-related areas of their lives too.

But is the Indian market hung up on power? Off-hand, I'd say it is. Talk to anybody in the selling end of the auto industry and he or she will tell you that customer queries, sooner than later, will come down to whether a car has power or not.

But what do people mean by power? Are they talking about torque? Or are they talking about cylinder displacement?

The fact is that most people are not very clear about what they mean by power. Let's see whether we can do something about that.

Assume a one pound weight is fixed to the floor. If you try and lift it with one pound of force, you would have expended energy but you would not have done any work. Now let's assume that you loosen the weight and apply sufficient force to lift th e weight one foot. You would have carried out one foot pound of work. And if you've lifted the weight one foot in one minute, the work would have been done at the rate of one foot pound per minute. And if you've hoisted the weight in one secon d, you would have done work at the rate of 60 pounds per minute.

What I'm trying to get you to understand here is that you'll have to deal with three variables -- force, work and time -- when you're evaluating what you call the power of a car.

Let's do a side-step here. Remember James Watt? That marvellous chap who gave the world the steam engine? Watt figured out that an average horse of his time could lift a 550 pound weight one foot in one second, thereby performing work at the rate of 550 foot pounds per second or 33,000 foot pounds per minute. He then went on to publish his findings, stating that 33,000 foot pounds per minute of work was equivalent to the power of one horse. Ergo, horsepower.

Hold on for a minute! We haven't quite finished as yet. In fact, we're just about getting to the fun part. What we'll do now is try and measure the units of force generated by a **rotating** gizmo -- your car's crankshaft, for instance. This ki nd of a force is basically a twisting force and is known as torque. A foot pound of torque is the twisting force needed to support one pound weight on a weightless horizontal bar one foot from the fulcrum.

What you need to understand at this point is that nobody measures horsepower by running an engine on a dynomometer. What people do is measure torque and then calculate horsepower by converting the twisting power of torque into the work units of horsepow er. Let's get back to that one pound weight hanging from a weightless bar. If you rotate the weight one full revolution against a one-pound resistance, you would have moved it 6.2832 feet. And done 6.2832 foot pounds of work.

Now Watt had said that 33,000 foot pounds of work per minute was equal to one horsepower. So we do some basic arithmetic and find out that one foot pound of torque at 5,252 revolutions per minute is equal to 33,000 foot pounds per minute of work which is, in turn, equal to one horsepower.

It should be obvious to you by now that torque -- and only torque -- counts as far as the driver of a vehicle is concerned.

Torque is what you **feel.** And horsepower is what you calculate. You can check this out for yourself. Spool up your car to its peak torque in first gear and then hit the gas. You'll feel the surge. You won't get this feeling if you start from a power p eak.

Let's look at it from another point of view. A car will accelerate hardest at its peak torque in any given gear. It won't do that below peak torque and it won't do that above peak torque. Horsepower, on the other hand, will continue to climb with the rpm even when you're past peak torque. That is, till the torque curve begins to drop faster than the engine rpm is rising.

I think you've got the idea. Enough of it, in any case, to look any salesman who's trying to get you with the old horsepower pitch in the eye -- and turn him down with a sneer.

Having gone on and on about engine torque, let me hit you with a whammy: Engine torque alone doesn't count! What counts is a thing called potential torque multiplication provided by the transmission, the final drive ratio and the tyre diamete r.

Horsepower, being the rate at which torque is produced, is an indicator of how much potential torque multiplication is available. The word potential needs to be stressed here. After all, if a car is not geared properly, you won't be able to use the engine horsepower optimally. The sad truth is that they just don't make cars with infinitely variable gear boxes which hold rpms at an engine's peak horsepower and, therefore, give you the best possible acceleration. So we'll just hav e to make do with finitely spaced fixed gearing. But we have problems here too. Auto makers, owing to considerations like durability, noise, fuel consumption and stuff like that, invariably compromise on the final drive gearing.

And then again, you can't get away from the fact that it's the torque applied by the tyres to the ground that actually accelerates your car, not the torque generated by the engine.

All in all, this whole business of torque versus horsepower is turning out to be quite a can of worms.

So we'll let it be and wind up with two simple things that you should bear in mind when buying a car.

* Check out the power weight ratio. This is the weight of the car divided by the maximum horsepower of the engine. It should give you an index of the accelerating ability of the rig.

* Ensure that the torque is bunched in the low rpm band. In India, that's where you need it.