DRIVE TRAIN POWER LOSSES:
DRIVE TRAIN POWER LOSSES:
In general, allow about 30-40 HP for internal consumption and driveline losses (alternator, compressor, etc.).
GRADE RESISTANCE:
Add all of the above power requirements at a given speed to determine how much horsepower total is being consumed.
To determine how much power is left for climbing grades, take the engine's maximum output horsepower at the corresponding RPM speed, subtract
the power required for driving on level road, and the difference can be applied to climbing (gradeability).
Power required to climb a grade is:
HP = percent grade x GVW x MPH / 37,500
A 35,000-pound bus on a 6% grade at 60 MPH requires:
HP = 6 x 35,000 x 60 / 37,500 = 336 HP
Using the above figures for level ground at 60 mph, one concludes that to climb a 6% grade in a 35,000 pound coach at 60 mph would require about
336 + 73 + 38 + 40 = approx. 487 HP.
The same coach on the same grade at 50 MPH requires only 387 HP.
ALTITUDE FACTOR (air density):
Remember also that a Naturally Aspirated (non-turbo) engine loses approximately 3% of its horsepower per 1,000feet altitude (above sea level).
This means that a NA coach that can climb a 1-1/2% grade at a given speed at sea level, will lose power and speed as it climbs due to the "thinner" air. At 11,000feet your 210hp engine has about 140hp. Heat also plays a part, cooler air is more dense and makes more power.
Also note that nowhere is the term "Torque" mentioned, as it has no value here.
People will tell you that a diesel's pulling/climbing power is in its torque, not its horsepower, WRONG!
Torque is useful for calculating horsepower, and you need to add RPM to get those horsepower numbers.
Torque is force, and is not a measure of work. Horsepower is work, and this is how you calculate how much speed/hill/etc. you can handle.
The torque at the wheel is what really matters, and this is dependent on gearing, which is determined by RPM and horsepower, not engine torque.
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VAGABOND’S HANDBOOK
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