Question about horsepower for car

In summary, the conversation discusses the amount of horsepower needed for a diesel car with a 250HP motor and weighing 3,500 pounds to go up a slight incline at an average speed of 20 mph. While the minimal power can be calculated using standard formulas, cars have additional inefficiencies due to friction, air drag, and other losses. A rough estimate of the work done to raise the car up the incline is provided, and it is noted that the horsepower equivalent is relatively modest. It is also mentioned that wind resistance should be taken into account when calculating the net force, and a formula for this is provided. Overall, a ballpark number for horsepower based on the given parameters is difficult to determine without more specific information.
  • #1
scott22
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I am wondering how much horsepower would be needed, or generated (not sure which term is right), if a diesel car with a 250HP motor, and weighs 3,500 pounds, is going up a slight incline (maybe 2 or 3 degrees) averaging 20 mph? Thanks.
 
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  • #2
The minimal power is given by the usual formulas for an inclined plane, but cars are quite inefficient and you have additional losses for friction, air drag, and other losses that are impossible to quantify with the parameters you gave.
 
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  • #3
A first cut would be to just estimate the work done raising the car as it goes up the incline.
20 mph is about 30 ft/sec and a 3 degree incline is about 1 foot in 15, so the car is raised 2 ft per second.
You will find that the horsepower equivalent is surprisingly modest.
 
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  • #4
Thanks for the info! Is it at all possible to get a ballpark number for horsepower based on the parameters I have given. If so, a thousand thanks!
 
  • #5
In 60 seconds, your car is going up 2ft/sec x60sec =120 feet.
It weighs 3500 pounds, so the work done in one minute is 3500x120 foot pounds= 420,000 foot pounds/minute.
Google one horsepower, it is 33,000 foot pounds/minute, so...
 
  • #6
Etudiant has given you most of it, you might also consider adding an estimate of wind resistance. The equation to calculate the net force would be:

99a6015b6a230860c9b1517b238e5de9.png

Wikipedia: Drag Equation

You can estimate the car's drag coefficient to be somewhere between 0.25 - 0.30 but is dependent on make/model and you will also need frontal area. You can look up some typical make/model drag area values (product of C.d and A) here: Wikipedia: Automobile Drag Coefficient

Once you calculate the drag force, calculate power (Power = force * velocity); for 20 mi/hr this number may be small, but at 40 mi/hr and up it will increase dramatically (velocity squared term).
 
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1. What is horsepower and why is it important for cars?

Horsepower is a unit of measurement used to describe the power and performance of a car's engine. It is important because it determines how much work the engine can do in a certain amount of time, which directly affects the car's speed and acceleration.

2. How is horsepower calculated for a car?

Horsepower is calculated by multiplying torque (force) by engine speed (RPM) and dividing the product by 5,252. This calculation is based on the original definition of horsepower, which is the amount of power needed to lift 33,000 pounds one foot in one minute.

3. What is the difference between horsepower and torque?

Horsepower and torque are both measures of engine power, but they represent different aspects of performance. Horsepower is a measure of how fast work can be done, while torque is a measure of the twisting force that makes an object rotate. In simple terms, horsepower determines how fast a car can go, and torque determines how quickly it can get there.

4. How does horsepower affect fuel efficiency?

Horsepower and fuel efficiency have an inverse relationship. This means that as horsepower increases, fuel efficiency decreases. This is because a more powerful engine requires more fuel to maintain its performance. However, advancements in technology have allowed for more efficient engines with higher horsepower, so the relationship is not always linear.

5. Does horsepower affect the overall performance of a car?

Yes, horsepower is a key factor in determining the overall performance of a car. It affects the car's speed, acceleration, and towing capacity. However, other factors such as weight, aerodynamics, and transmission also play a role in performance. A car with high horsepower but poor aerodynamics or a heavy weight may not perform as well as a car with lower horsepower but better overall design.

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