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 working?

In the US, all light duty vehicles are rated using the same testing procedures defined by the Society of Automotive Engineers. It is horsepower at the rear wheels with all accessories installed (A/C is likely turned off).When you get to medium duty vehicles, I believe the horsepower is measured "at the crankshaft", but again with all accessories (probably not A/C).The important thing is that it is done CONSISTENTLY across all manufacturers.

There is a lot more leniency in the SAE J1995 or J1349 test requirements than most think. Attached is an old J1349 test standards. I have the current J1349 and J1995 standards, but cannot link them. However, not much has changed.J1349 Test StandardPages 10-12 discusses what you are looking for.J1349 requires most accessories while J1995 doesn't. However, that does not mean the manufacturers do not test with accessories on J1995. Some do when they know exactly what the engine is used for making them no different than J1349. They have to use J1995 because they are not building the complete vehicle.

theoldwizard1 wrote:In the US, all light duty vehicles are rated using the same testing procedures defined by the Society of Automotive Engineers. It is horsepower at the rear wheels with all accessories installed (A/C is likely turned off).When you get to medium duty vehicles, I believe the horsepower is measured "at the crankshaft", but again with all accessories (probably not A/C).The important thing is that it is done CONSISTENTLY across all manufacturers.SAE Net Horsepower includes all accessories and emission controls, but is measured at the crankshaft.https://en.wikipedia.org/wiki/Horsepower#SAE_net_power

All manufactures rate horsepower at the crankshaft when it advertised. It is full accessories and emissions.Cars in the 50, 60, 70's were rated with no accessories. That is why if you were to test them today you see they are lower than was advertised and slower then what they should be for rated power.On average when you do a dyno pull in a manual you expect a 10 to 15 percent loss through the drive train. In auto 15 to 20 percent loss. This is average and it varies case by case. I will use my WS6 for an example. It was rated at 320 to crank by GM. It dynoed at 328 bone stock. Underrated by GM. You hear about that one on a lot of cars. It also depends on what kind of Dyno and conditions that day. The rated HP from the manufacture is done in controlled conditions and has to be repeatable.

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.

Rated engine power | Good Sam Community

ShinerBock
Explorer
Nov 14, 2019
There is a lot more leniency in the SAE J1995 or J1349 test requirements than most think.

Attached is an old J1349 test standards. I have the current J1349 and J1995 standards, but cannot link them. However, not much has changed.

J1349 Test Standard

Pages 10-12 discusses what you are looking for.

J1349 requires most accessories while J1995 doesn't. However, that does not mean the manufacturers do not test with accessories on J1995. Some do when they know exactly what the engine is used for making them no different than J1349. They have to use J1995 because they are not building the complete vehicle.
theoldwizard1
Explorer II
Nov 14, 2019
In the US, all light duty vehicles are rated using the same testing procedures defined by the Society of Automotive Engineers. It is horsepower at the rear wheels with all accessories installed (A/C is likely turned off).

When you get to medium duty vehicles, I believe the horsepower is measured "at the crankshaft", but again with all accessories (probably not A/C).

The important thing is that it is done CONSISTENTLY across all manufacturers.

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