Buying a new car and beating the verbal barrage

By Barry Lake

YOU have decided to buy a new car. You head down to the local dealer where a fresh young salesperson approaches you and begins to explain the finer attributes of the shiny new vehicle sitting in front of you.

The words come thick and fast: EFI, disc brakes, auto box, 2.0-liter with 98 kilowatts and 165 Newton metres. But what does it all mean. The Automotive Post explains...

Question: What is front wheel drive (fwd)? What is rear wheel drive (rwd)?

Answer: Nothing to do with steering, this refers to the wheels which transfer the motive power to the roadway. In the past, it was most common for power from the car's engine to be transmitted via gearbox, tailshaft and rear axle to the rear wheels. Now, it is becoming increasingly common in modern cars for power to go directly to the front wheels.

Q: What is a carburetor?

A: This is a device which mixes fuel with air in the correct proportion for efficient combustion within the car's engine. Air wrawn into the engine passes through the carburetor. At one point the air passage narrows into a venturi where the thus-increased speed of the air creates a low pressure area which in turn draws the fuel through a metering jet and mixes it with the air as it enters the engine.

Q: What is electronic fuel injection?

A: Fuel injection is a more modern method than the carburetor of mixing fuel and air. Electronic fuel injection is the latest and most efficient injection system. A high-pressure fuel pump supplies the fuel and this is injected into the inlet ports just before the inlet valves. A preprogrammed computer meters the fuel delivered via the injectors to a degree of accuracy which could not possibly be achieved with a carburetor. The result is better power output and greater fuel economy.

Q: What is automatic transmission?

A: In simple terms, it is a gearbox which changes gear without any input from the driver. There is no clutch or clutch pedal for the driver to operate. A fluid-filled "torque converter" provides slip for starting from rest and this gradually takes up automatically. Ratios are selected either by precalculated pressure within the hydraulic system or, in later versions, by computer control and electronics.

Q: Why are disc brakes better than drum brakes?

A: They are self-adjusting, so that brake pedal height is not lost throughout the life of the pads. The exposed disc cools far more efficiently than the enclosed drums. Worn pads are easier to replace than the linings in drum brakes. And, after driving through water, the water flies off the disc instantly, while water held within a drum brake can seriously reduce braking efficiency.

Q: What is engine capacity?

A: Engine capacity can be explained as the volume of air displaced by one of its pistons as it rises from the lowest point in its stroke to the highest point in its stroke, multiplied by the number of pistons (or cylinders) in the engine.

Mathematically, this is half the diameter of the piston bore, multiplied by itself (squared), multiplied by Pi (3.142), multiplied by the length of the stroke, multiplied by the number of cylinders.

This is usually calculated in centimeters and cubic centimeters, sometimes (as in the U.S.) in inches and cubic inches. Small four-cylinder cars usually have engines between around 1.0 liters (1000 cm3) and 2.0 liters in capacity.

Q: What is torque and power?

A: The relationship between these two confuses many people. In simple terms, torque is the twisting force generated by the engine -- similar to that provided by a cyclist pushing the pedals of a bicycle.

Power represents work done in a given time. It is a function of torque multiplied by the speed of the engine (revolutions per minute, or rpm).

Thinking of the bicycle again, pushing very hard, but slowly, on the pedals (torque) is one thing and this will get you up a steep hill, but pushing hard while pedaling quickly (power) will get more work done -- or cover more distance -- in any given period of time.

Q: What is the difference between petrol-powered and diesel- powered engines?

A: A lot, in fact. While both have pistons going up and down in cylinders, operating the crankshaft via connecting rods, their combustion processes are entirely different.

A petrol engine relies on a spark plug to ignite the fuel-air mixture but a diesel engine -- more correctly known as a "compression ignition" engine -- has a very much higher compression ratio and the fuel-air mixture is ignited by the temperature created when the mixture is compressed to a very high pressure.

Diesel engines, because of the forces involved in this process, are built much heavier and stronger than petrol engines. Diesels also have what is called "direct injection", meaning the fuel is sprayed directly into the cylinder at precisely the right time for correct ignition and combustion.

A fuel pump which operates at extremely high pressure is required for diesel injection.