Car Glossary India - Index B

Brake horsepower or BHP is a commonly used unit for measuring power of a car engine. This unit of measurement traces back to the days of the industrial revolution, when a steam engine was rated by how many horses it replaced. It is slightly different from the unit Horsepower (HP). The higher the BHP figure, the more powerful is the engine.

Bore/stroke ratio is related to the engine speed. The bore is the diameter of the cylinder and the stroke is the length that piston travels. A piston engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel), whereas it is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel). An oversquare engine is generally more reliable, wears less, and can be run at a higher speed. An undersquare engine usually has a lower redline than an oversquare one, but it generates more low-end torque. Engines are designed to have high bore to stroke ratios to spin fast and achieve top speed as well as to maintain piston speed and friction.