TRUCK SERVICE MANUAL
to the discretion of the supplier. The additives must be
Brake Horsepower = Lbs. (on Dyno. Scale) x Engine
RPM
antifoaming, anti corrosive antigumming.
The fuel,
additives, and color dye must be non-toxic and non-
Dynamometer Constant
harmful to personnel.
Example: Dynamometer in operation has brake constant
Chemical And Physical Requirements
of 500. Scales show a reading of 50 pounds and
tachometer shows engine rpm of 1600.
Kinematic Viscosity at
Brake Horsepower = 50 x 1600 = 160
100 deg F Centistokes, ASTM D445 .................... 2.5 3.3
500
Viscosity at 100 deg F [38 deg C] Saybolt Universal
The above formulas apply to engine dynamometers only.
(SUS), ASTM D2161 ........................................ 34.4 37.0
Where chassis dynamometers are used, a factor of
Specific Gravity at 60 deg. F, ASTM D287......... 820.830
approximately 25% must be used to compensate for
Gravity, Degrees API, 60 deg F, ASI M D287 ........ 41-39
gear ratios, tire size, etc.
Flash Point, P.M., Closed Cup, ASTM D93 160 deq F Min).
Procedures of Converting Horsepower
Color, ASTM D1500 ............................................. 2 Max.
1. All horsepower ratings In fuel pump data are
Cummins test ratings. Cummins test horsepower ratings
Water ASSTM D01796 ............................................. .005
are made at 500 ft. [152 m] altitude and 80 deg, F [26.7
Corrosion, ASIM D130....................... Must Pass Class 1
deg. C] temperature, therefore, test horsepower is about
4% below the ratings made at sea level and 60 deg. F
Galvanic Corrosion, ASTM-5322-1 ................ Must Pass
[15.6 deg. C]. To convert sea level horsepower ratings
Sulphur % Weight, ASTM-P129, D1552 .................... 0.4
to your location (see Table 5-1-1) deduct 3% per 1000 ft.
Distillation at 20% point, ASTM-D86 ...... 440 deq. F Min,
[305 m] above Sea Level and 1% per 10 deg. above 60
deg. F [15.6 deg. C].
Sediment - Using a 10 Micron filter, 22,260 particles per
millileter are permissible. Using a 40 Micron filter, 195
Notes:
particles per millileter are permissible. Using a 50
a.
Turbocharged engines develop the stated
Micron filter, 5 particles per millileter are permissible.
horsepower from sea level to the altitude given in engine
Mobile Oil Company Type MC L-41 is one source that
operators manuals.
meets the above requirements.
b. All engines derated in power only, or in power and
Instruments
speed combined, need not be converted for any
difference between Cummins and Sea Level standards.
A fuel pump cannot be calibrated with any greater
precision than that of instruments on the test stand.
2. Data given in Table 5-1-1 is Intended as a guide to be
Pressure, speed and flow measurements must be very
used In the conversion of horsepower as expressed in
accurate, since these are the factors which determine
one system to that of another system. Standard test
the pump characteristics.
conditions vary from one system to another as noted.
The instruments on a fuel pump test stand and engine
Note: The Din (German) horsepower ratings includes fan
test stand have the accuracy required for precision
horsepower whereas the other systems listed do not
calibration and testing when new, but this accuracy must
include the horsepower required to drive the engine
be periodically checked and maintained.
cooling fan or the battery charging generator. In general,
approximately 10 percent adjustment of horsepower
General
rating will make up the difference, When the horsepower
CAUTION
required to drive the fan and the generator is known, the
exact adjustment in net horsepower may be made.
Cummins Engine Company, inc.
assumes no
responsibility of damage if fuel pump is calibrated to a
3. Including differences in altitude and temperature in
different specification than listed for a specific engine
the standard test conditions, the following conversion
model and Pump Code.
must also be made in addition to the conversion from the
difference in Ft. Lbs./Sec., so the total conversion
Formula to Determining SAE Brake Horsepower
becomes
Evaluation of engine performance during testing is for
Cummins, SAE or British HP = Metric or Din
the most part, based on accurate horsepower readings.
Therefore, it is imperative that the following formulas be
(German) HP x .9863
used with test procedures.
The basic formula to
Metric or Din (German) HP =
Cummins, SAE or
determine brake horsepower is as follows:
British HP x 1.0139
Brake Horsepower = Torque In (Ft. Lbs.) x Engine RPM
Note: The above conversion disregards the very slight
5252
percent difference in relative humidity between Cummins
Most engine dynamometer manufacturers provide a
and SAE or British systems.
figure known as a "brake constant" with each
4. Units of measurement conversions from one system
dynamometer. The constant simplifies the process of
to another.
computing brake horsepower since only engine rpm and
the scale reading (in pounds) need be found by the test
mechanic. The formula used with a known constant Is
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