I am assuming its the RAC Horsepower figure youre talking about which is often listed alongwith with metric hp, similar to to what we have german PS ratings alongwith hp in our indian brochoures RAC horsepower
This measure was instituted by the Royal Automobile Club in Britain and used to denote the power of early 20th century British cars. Many cars hence had names such as "40/50hp", which indicated the RAC figure followed by the true measured power.
RAC horsepower cannot be given as a proportion to metric power. Instead, it is derived from dimensions of the engine and certain assumptions about engine efficiency. When invented, it gave a rough guide to its true power rating; as new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations which used the rating for tax purposes.
RAC h.p. = {D^2 * n}/2.5 where
D is the diameter (or bore) of the cylinder in inches
n is the number of cylinders
This is equal to the displacement in cubic inches divided by 10pi then divided again by the stroke in inches. WL & WL-T are model codes for the Ford 2500cc diesel engines; naturally aspirated and turbo variants. |