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<< Previous Message No. 28 Next >>
Author: dr funda
Time: 01/09/00 12:50 PST
This is a reply to message no. 27 by rok
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Current Topic:
Diesel engine torque and horsepower conversion formulas
rok,

You have brought out a very good issue that seems to confuse a lot of us so I think I'll discuss this one in detail:

Short answer:

100PS@3500rpm (DIN) ~ 98.632Hp@3500rpm (SAE Net)
24.5kg-m@2000rpm (DIN) ~ 174.8lbf-ft@2000rpm (SAE Net)

The SAE Gross numbers are impossible to get without knowing the equipment to which the engine is attached. A typical passenger car eats away about 20% of the gross engine output so if you must guess, divide the SAE Net numbers by 0.8 to get some idea what the SAE Gross numbers might look like.

Long answer:

First of all, there are TWO definitions of horsepower in SAE J1349, Gross and Net. The SAE Gross is the engine output measured at the shaft, without the transmission and other power-robbing attachment; while the SAE Net is the net output after all the power-robbing add-ons have been taken into account. The DIN 70020 standard, however, is always NET, that is, the output after the overhead.

Because you already have the DIN numbers, I'll assume that this diesel engine is already installed on a vehicle, since the DIN rating can not be defined without knowing what kind of equipment the engine is attached to. The SAE Net horsepower is roughly the same as DIN, with some minor uncertainties and a small 1.0139 scaling factor.

The uncertainties come from the fact that these standards use different test methods under slightly different environments. For example, SAE J1349 calls for 77°F(25°C) and 29.38 in(746.3mm) Hg; while DIN 70020 is performed under 20°C and 750mmHg. The 1.0139 factor comes from the converstion of  the 'standard' horsepower (745.7W) used in SAE to the metric horsepower (735.5W) used in DIN.

Since the environmental variables are very similar between SAE and DIN, it is safe to believe that most engines behave simillarly under these two conditions. So, to convert DIN horsepower to SAE Net, simply divide the DIN number by 1.0139.

The SAE Gross, remains unknown, becuase we don't know how much power the overhead is robbing. In the short answer, I suggested 20% but that is a very very rough guess. The data has to be obtained from the manufacturer. (Note: The SAE Gross has not been used in the US since 1972)

I hope this clarifies a thing or two. If you have any question, feel free to let us know.


eFunda Staff





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