Car engine torque

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  • #1

Main Question or Discussion Point

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?
 

Answers and Replies

  • #2
688
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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
586
2
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
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 dont have the power at each RPM or speed.
 
  • #6
688
1
Welcome to you back. well i guess you mean multiplied by rev/s not rpm. The problem is i dont 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
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. Im 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
2,017
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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).
 
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