Horsepower or Torque? DIN or SAE?
Date: Tuesday, November 18 @ 08:39:52 EST
There are basically two differences between a DIN and a SAE horsepower rating:
One difference is in the parameters for a measurement: Horsepower is defined as work done over time. One SAE horsepower is the amount of power necessary to lift 550 pounds 1 foot in 1 second, or 33,000 lb.ft./minute. One DIN horsepower is the ability to lift 450000 kg one cm in one minute. For the same power the SAE measurement is thus 98.629% of the metric DIN measurement. 100 SAE hp = 101.42 DIN hp = 74.6 kW
If you see the term bhp, it just means "brake horsepower", which is the actual usable horsepower delivered to the rear wheels of the car. It is so named because a brake is applied to determine how much pressure is needed to stop or absorb the power. Bhp could reference either DIN or SAE horsepower. Often, however, brake horsepower is measured with no load from a chassis or any accessories attached to the engine whatsoever. It’s also called gross horsepower.
In vehicles, torque measures the turning force generated at the wheels. A high horsepower rating generally indicates the ability to sustain higher top speeds, while torque signifies a vehicle's acceleration and ability to pull heavy loads.
Horsepower is effectively torque times rpms, with the exact formula being
HP = Torque x 2 x Pi x rpm (Pi=3.1416…)
so if you keep the same amount of torque and double the revs, you double the effective horsepower. This is why most engines have the highest horsepower rating at higher RPMs. And along those lines, you can have an engine that has lots of horsepower at higher RPMs, but not much energy at lower RPMs where it counts off the line, so often torque ends up being a more interesting measurement than horsepower.
The other difference is in the engine configuration for the test: While DIN (Deutsche Industrie Normen) 70020 and thereunder DIN 6270 requires the efffective HP to be measured on an engine in standard production configuration, i.e.: with stock intake and exhaust, fan and waterpump or cooling blower, fuel pump, fuel injection pump and no electric load alternator, in the U.S.,vehicle manufacturers can test for horsepower and torque in a variety of ways. SAE J1349 Engine Power Test Code – Spark Ignition and Compression Ignition – Net Power Rating Standard specifies a basis for net engine power rating, and a method for determining net full load engine power with a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.
The current test, which originated in the early '70s and was last reviewed in 1995, allows OEMs to claim horsepower and torque figures higher than what most owners will actually experience. The SAE –Society of Automotive Engineering - Power Test Code Committee , is currently revising its standard for measuring horsepower and may suggest that OEMs have an independent observer verify the numbers they claim for horsepower and torque. The standard will also set a procedure for how to test torque, which is also heavily advertised by car manufacturers.
According to SAE, the revised standard is expected to be written by the end of 2003. An SAE advisory committee will then decide whether to adopt the procedure and the use of outside witnesses, such as Underwriters Laboratories Inc., to verify OEMs' claims.