Rated engine power
How do manufacturers, presently, determine how to rate their engine's crankshaft horsepower? Is the cooling fan engaged and drawing air? Alternator charging? Power steering pump and A/C installed and ...
Forum Discussion
Groover wrote:
On a related subject I would still like to know what the difference is between "certified horsepower" on the medium duty and apparently not certified horsepower in pickups. Also, why do diesels consistently dyno much closer to rated horsepower than gas engines? There should be only one way to rate horsepower and that is at the rear wheels with all standard items on. On diesels that should probably include numbers just before and just after particulate filter cleaning.
"Certified power" just means that they had a third party SAE licenced person witness them do the J1349 or J1995 test.
As far as power at the wheels, this is not possible for all applications. For instance, Cummins certifies the power of their engine and sends it to Peterbilt to sit in a warehouse until that specific engine and power level is needed for a truck that is ordered. Peterbilt then puts the engine into the truck that can have one of thousands of different cab, trans, PTO, and drive line configurations. If they put a fifth wheel on it, then it is a complete tractor and they would have to dyno every one that comes off the floor with a different configuration. If they don't put a fifth wheel or box on it, then it is not a completed vehicles and it gets sent to a final builder who would up-fit the truck with various different things that would also effect power output. In some cases, the final builder is the customer.
