Calculating Car Engine Torque: A Guide to Plotting the Torque Curve

In summary: You can measure things like manifold pressure and air flow too.Do you have an engine horsepower vs rpm curve ? Often, the manufacturer will publish these.If so, you can compute the torque at any point with the relation: power = torque X rpm.If you don't have this graph, let me know. There are other things we can do.
  • #1
I have a car engine specs and I wanted to estimate the torque at each speed and plot the torque curve.

I have calculated the road load or the running resistance force for all gears at different RPM's and found the speed (m/s) for each RPM.

How to estimate the torque of the engine in order to plot the torque curve?
 
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  • #2
welcome to PF.

Do you have an engine horsepower vs rpm curve ? Often, the manufacturer will publish these.

If so, you can compute the torque at any point with the relation: power = torque X rpm.

If you don't have this graph, let me know. There are other things we can do.
 
  • #3
Studen8989 said:
I have a car engine specs and I wanted to estimate the torque at each speed and plot the torque curve.

I have calculated the road load or the running resistance force for all gears at different RPM's and found the speed (m/s) for each RPM.

How to estimate the torque of the engine in order to plot the torque curve?
There are programs, such as "Desktop Dyno", for estimating engine power. Accuracy can be quite good, if you have enough data about the engine to input. What specs do you have -- bore & stroke, camshaft, compression, cylinder head volume, ...?

Bear in mind, results are maximum (full throttle) torque values. This applies to software calculations and physical (dynamometer) measurements. (It's easy enough to do a dyno run at part-throttle, but you would have to specifically request it from the dyno operator.)
 
  • #4
I have estimated a gear ratios for this design.

I have different RPM's of the car and I have calculated they're corresponding speed at each gear at each RPM. And I also have calculated the road load at each gear and at each RPM.

I need to find the torque I have the running resistance force, mass, Cd, Cw.
 
  • #5
edgepflow said:
welcome to PF.

Do you have an engine horsepower vs rpm curve ? Often, the manufacturer will publish these.

If so, you can compute the torque at any point with the relation: power = torque X rpm.

If you don't have this graph, let me know. There are other things we can do.

Welcome to you back. well i guess you mean multiplied by rev/s not rpm. The problem is i don't have the power at each RPM or speed.
 
  • #6
Studen8989 said:
Welcome to you back. well i guess you mean multiplied by rev/s not rpm. The problem is i don't have the power at each RPM or speed.
Like pantaz said, there are software packages available for this. I use "Engine Analyzer" when I have time to tinker with these things. If you had the data pantaz mentioned, I could try to set something up if I can find a few minutes. The camshaft lift and duration is important for the shape of the power curve.

What is the make and model of the car?
 
  • #7
edgepflow said:
Like pantaz said, there are software packages available for this. I use "Engine Analyzer" when I have time to tinker with these things. If you had the data pantaz mentioned, I could try to set something up if I can find a few minutes. The camshaft lift and duration is important for the shape of the power curve.

What is the make and model of the car?

Im trying to build up my own car, I just have some issues with stability. I am trying to build a 1.8L TDCi, 0-60mph is around 5.67sec and 50-70mph is 5.4 secs. However, it has bad fuel economy and top speed performance.

anyway thanks
 
  • #8
I know this isn't answering the question (because in reality getting an accurate answer without measuring anything will be a fluke anyway).

Why not just stick it on a dyno? Runs can be had for about £30-60, the US will probably be equavilant ($100 maybe).
 

1. What is engine torque?

Engine torque is a measure of the rotational force produced by an engine. It is typically measured in pound-feet (lb-ft) or Newton-meters (Nm) and is an important factor in determining a vehicle's acceleration and towing capabilities.

2. How is engine torque calculated?

Engine torque is calculated by multiplying the force produced by the engine (in pounds or Newtons) by the distance from the center of the crankshaft to the point where the force is being applied (in feet or meters). This calculation can be done at various engine speeds to create a torque curve.

3. Why is it important to plot the torque curve?

Plotting the torque curve allows you to visualize how much torque the engine is producing at different speeds. This information is crucial in understanding how the vehicle will perform in different driving situations and can also help with tuning the engine for optimal performance.

4. What factors influence engine torque?

Engine torque is influenced by several factors, including the size and design of the engine, the fuel-air mixture, the ignition timing, and the exhaust system. Other factors such as temperature and altitude can also affect engine torque.

5. How can I use the torque curve to improve my vehicle's performance?

By analyzing the torque curve, you can identify any areas where the engine may be lacking in torque and make adjustments to improve performance. For example, if the torque drops off at higher engine speeds, you may need to adjust the fuel-air mixture or ignition timing to provide more torque in that range. Additionally, using the torque curve can help you determine the appropriate gear ratios for your vehicle to optimize acceleration and towing capabilities.

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