What is Horsepower
What is horsepower?
If you've spent any time around cars or car people you've heard the term horsepower. Horsepower is very important to some car owners. For race car, muscle car and high performance car fans, the more horsepower the better. Horsepower means power and power means fast. Up until 1971, engines were advertised with what is called brake horsepower (Bhp). In 1972, this all changed.
The term horsepower was coined by an engineer named James Watt. Watt was using horses to lift coal from coal mines and wanted a way to measure the power available from different horses. He found that, on average, a mine horse could perform 22,000 foot-pounds of work in a minute. He then increased the number by 50 percent and came up with a measurement of 33,000 foot-pounds of work in one minute. This measurement eventually became known as horsepower.
Muscle car owners love to brag about horsepower. A 1969 Ford Torino Cobra comes equipped with a 360 hp engine. A 1974 Pontiac Catalina comes standard with 155 hp engine. Which car would you rather own? If you like to read classified ads for cars, (and who doesn't) you may notice that older cars seem to have higher horsepower engines. This really isn't true. Although the Cobra most definitely has a more powerful engine than the Catalina, the two horsepower ratings are not representing power the same way.
Up until 1971, engines were listed with what is called brake horsepower (Bhp) Brake horsepower is a calculation where the engine horsepower is measured at the point of output with no load from a chassis or any accessories and with fuel and ignition operations under ideal conditions. Brake horsepower is often called gross horsepower today. This figure was often used for advertising purposes up to 1971.
An accessory is anything attached to the engine, by any means, which is not required for basic engine operation. By this definition, this would include a power steering pump, smog pump, air conditioning compressor and an alternator.
Ideal conditions, often called laboratory conditions, are standardized settings for use during horsepower measurement. During the 1960s they consisted of a barometric pressure of 29.92 Hg and a temperature of 60 degrees F.
Net horsepower, also called road horsepower, (Rhp) is a calculation where horsepower is measured after the load from a chassis and accessories. Essentially, this is the power available at the drive wheel or wheels of a vehicle. This type of horsepower is also called SAE net horsepower.
The SAE or Society of Automotive Engineers is a group responsible for setting various standards within the automobile manufacturing industry. Founded in 1905, the SAE publishes many new, revised, and reaffirmed standards each year in three categories: Ground Vehicle Standards, Aerospace Standards, and Aerospace Material Specifications. Standards allow entire countries to talk to each other in a common language.
Horsepower ratings on engines were becoming a bit misleading in the late 50s and early 60s. The average car owner does not think about how much power is needed to run an A/C compressor or an alternator. Automatic transmissions and electric accessories also became popular in the late 60s and early 70s which sucked even more power from the engine. To keep comparisons on equal footing, the SAE decided to step in and began rating engines with the entire car attached. As a result, horsepower seemed to drop on many popular American muscle cars. Although two cars could be identical, the 1970 model would have a higher horsepower engine rating than the 1972 model. Most people understood the change, but some car owners were outraged and began buying pre-1971 cars so they could brag their engine ratings. Don't be fooled. A 1972 Chevelle SS will get you from 0 to 60 just as fast as the 1971 model.
