The airbag is a "passive restraint safety system" for cars. Air bags are available for the front (passenger and driver) and for the side, and are designed to inflate only on severe frontal or side collision. The system works in the following manner - there are sensors in front of the car, which on impact activate a small hermetically sealed container of solid sodium azide. The sodium azide ignites in a controlled manner generating a large amount harmless gas. The gas, which is generated in less, then 0.05 seconds, inflates a porous bag that protects the occupant from hitting the steering wheel and dashboard. The porous bag deflates again so fast that the deflation begins even the before the inflation is entirely complete, and is complete in 15 -20 seconds. The system is designed to inflate only on a certain minimum impact. (approximately equivalent to hitting a wall at around 15-19 mph.

Bore is the measurement of the diameter of each cylinder, and stroke is the distance the piston travels one-way within the cylinder. By first determining the area of the cylinder and then multiplying that by the stroke, you can obtain the displacement for each cylinder. Multiply that by the number of cylinders for the total engine displacement (engine size).

Coils springs form a part of the contemporary space-saving suspension system of the car. These are thick, coiled steel springs that carry the weight of the car. By varying the thickness and type of steel, different levels of comfort, handling and load-carrying ability can be provided.

Compression ratio is the ratio of the combustion chamber (cylinder) volume with the piston at the bottom and the piston at the top. Ratio refers to how much the fuel-air mixture in the cylinder needs to compressed before ignition. The higher the compression ratio normally means greater power. A typical petrol engine has a compression ratio of 8:1 or 9:1, while a diesel engine has a ratio of 20:1

Catalytic converter is a device fitted to the exhaust of a car to reduce the toxic emissions (incompletely burnt fuel) like carbon monoxide and Nitrous oxide from the engine. The system consists of metallic or ceramic honeycomb structure over which various catalysts are coated (the honeycomb structure increases the total surface area, thus allowing maximum catalyst to come in contact with the emitted pollutants). The catalysts used are palladium and platinum metals - which convert the unburned fuel and carbon monoxide into carbon dioxide and water, and rhodium - which converts nitrogen oxide gases into nitrogen and oxygen.

A catalytic converter can reduce harmful emissions of a car by 60 to 90%, although it causes a slight increase in the amount of carbon dioxide. A car fitted with a catalytic converter, necessarily needs to use unleaded fuel, since the lead in the fuel forms a film over the catalysts, damaging the converter and rendering it ineffective.

The differential houses a system of gears (bevel and ring) in the transmission system of the car, which enables different wheels to run at different speeds. While cornering the outer-wheels cover a larger distance and needs to turn faster than the inner wheels. The differential allows wheels on the same axle to turn at different rates.

This is measured in cc or litres, and refers to the total volume of all the cylinders in the engine. Volume of the cylinders and therefore the engine capacity is calculated by multiplying the area of each cylinder with the length of the piston stroke. Larger the engine capacity, greater is fuel that can be burned in each cycle, resulting in greater power to the car.

Refers to the number of wheels to which the engine's power is distributed. Normally the engine power is directed to only one axle (either the back or the front) thus distributing power to only two-wheels. In a front-wheel drive the engine rotates only the front-axle, while in a rear-wheel it rotates the rear-axle. In a four-wheel drive the engine power is distributed to both the axles (and therefore to all the four-wheels) thus affording greater traction especially required for off-road vehicles.

The fuel-injection system, like the carburetor prepares the correct mixture of air and fuel for the engine. The system receives fuel from the fuel-tank through a mechanical pump. This fuel is received under relatively low pressure, and is injected into the engine under higher pressure, at a precise, pre-determined time. A multiple-point fuel injection system means each cylinder of the engine has a separate electronically controlled fuel injector. The system ensures that there is always the right air-to-fuel ratio in the engine, to ensure optimum combustion under varying conditions.

Traditionally engine cylinders had two valves - one for intake of the fuel-air mixture and one to let out the exhaust. Contemporary engines have multiple valves (usually four per cylinder) to facilitate better flow of the fuel/air mixture into the engine and exhaust gases out of the engine.

The transmission system essentially "transmits" the turning movement of one shaft to another shaft, and is ultimately responsible for the power reaching from the engine to the wheels. Transmission is done through a pair or even three gear wheels. The ratio of the number of teeth on the gear wheels is termed as the gear ratio, which in turn determines the torque ratio (the turning force on the out-shaft as compared force on the input shaft).

An exhaust-driven pump (i.e. the turbine driving the pump uses the hot gases of the exhaust) which compresses intake air and forces it into the intake manifold at higher than atmospheric pressures. The increased air pressure allows more fuel to be burned and results in increased horsepower being produced. A turbo-charged engine consumes slightly more fuel, but gives greater power to the car.

This indicates the total volume of all the cylinders put together in an engine.
Example:
Number of cylinders = 3
Diameter of cylinder = 9 centimeters
Length of cylinder = 10 centimeters

Note: 3.1416 is a constant called 'pie' and is used in calculating area or volume of geometric figures like cylinder.

A horse power is the power of one horse, or a measure of rate at which a horse can work. A 10 hp engine for example do the work of 10 horses.

Now work can be done slowly or fast. The rate at which work can be done is called power.

The horsepower output of an engine is measured in terms of BHP or Brake Horse Power. The name is derived from the braking device which is used to hold the engine stationary while it is trying to move, while the horse power is measured in labs on a dynamometer.

The BHP of an engine indicates the amount of power an engine can produce at a certain engine speed at wide open throttle (or accelerator fully pressed down)