Easily Determine Torque and Horsepower (w/out dynamometer)

[Dooder]

Over the past couple of weeks, I have been working on a physics project to find the horsepower and torque of my car without the use of a dynamometer. Attached is my work and a link to my research. I encourage anybody to take a look who may be interested in finding the torque or horspower of their car in different sections of their drivetrain, or anybody who is just interested in the physics behind it. http://bit.ly/1WwQ9AM.

I would like to start off by saying there are MANY variables that go into a calculation like this such as torque lost to friction, RPM range, gear the driver is in, rear diff. ratio, etc. After researching different concepts, I discovered that someone can find the torque of their car at the rear wheels simply by using the equation (values in metric units), linear acceleration found by filming speedometer in slow motion and using A=V/T:

Torque = Mass (of car) x Linear Acceleration (of car) x Radius (center hub to ground)

The above equation is derived from a basic equation for finding torque:

Torque = Force (perpendicular to pivot) x Distance (from pivot)

By substituting force with F=MA, there is no need to directly calculate turning force. After using the above equation and converting the torque from metric units (Nm) to imperial units (ft lbs), and then figuring out the ratio of the gears the torque is emitted through, someone can also find the theoretical horsepower of their engine (actual value of engine will be more because of drivetrain loss ~%15), using the equation:

Horsepower = (Torque x RPM) / 5252

Thanks for reading and leave a comment if you have anything to add, this thread will be a work in progress as I simplify the calculations and make it easier to find the acceleration of a car. Also attached are a couple pictures of the setup I used to determine the acceleration for later analysis with LoggerPro.

[havelegs]

Wow, this is very interesting.

[rvadim76]

Long reading but interesting indeed. Will provide my feedback once I am done ))

[Mr. Stacy]

To be safe, I would recommend wearing a helmet with a face-guard at the minimum. Even a small fender bender might find you with an iPhone embedded in your forehead.

[rvadim76]

Ok..QQ: what was your top numbers for TORQUE and POWER (at redline) ?

Do you think you can do the same computation by doing data log (SCT or Diablo Sport or any similar) devices?

Thanks

[rvadim76]

Originally Posted by Mr. Stacy

To be safe, I would recommend wearing a helmet with a face-guard at the minimum. Even a small fender bender might find you with an iPhone embedded in your forehead.

That's why I prefer a data-log

[velocity149]

Really cool concept. The only problem you'll find, is that the visual measurement (slow-mo of speedometer) will not be very accurate. the Speedo lags when under quick acceleration, as does the tach.

[rvadim76]

I think similar concept is being used by some portable devices which are capable to estimate the power & torque. Keep forgetting what dev. is capable to do so.
But I agree, really cool idea!

[rvadim76]

So how did you estimate the 295.19 ft lbs at the crank? Is it MAX torque or it's related with 2500rpm?

If I simply estimate:
Horsepower = (295 ft lbs x 6000 RPM) / 5252 I get 337 hp at 6000 RPM which could be truth for the rwhp, but not for the crank hp, so I am a bit confused, I guess I am missing something..

[nosmr2]

Originally Posted by rvadim76

I think similar concept is being used by some portable devices which are capable to estimate the power & torque. Keep forgetting what dev. is capable to do so.
But I agree, really cool idea!

Like one of these: http://www.gtechpro.com/ss_fanatic.html

[CapeCruisin]

Originally Posted by rvadim76

So how did you estimate the 295.19 ft lbs at the crank? Is it MAX torque or it's related with 2500rpm?

If I simply estimate:
Horsepower = (295 ft lbs x 6000 RPM) / 5252 I get 337 hp at 6000 RPM which could be truth for the rwhp, but not for the crank hp, so I am a bit confused, I guess I am missing something..

Check out his slideshow.
Also, L99 = 400HP, LS3 = 425HP

[Dooder]

Originally Posted by rvadim76

Ok..QQ: what was your top numbers for TORQUE and POWER (at redline) ?

Do you think you can do the same computation by doing data log (SCT or Diablo Sport or any similar) devices?

Thanks

Yes, those devices are designed to make this process easier. Being that I had to create a project from scratch and understand the physics behind how such devices work, I wanted to figure out a way that allowed anybody to find the torque and hp of their car with things they have around the house; i.e. smartphone, wooden ruler, computer.

I have not yet tested 4k-5k rpm range which should be max torque and power. I'll make sure to update thread when I do.

[Dooder]

Originally Posted by rvadim76

So how did you estimate the 295.19 ft lbs at the crank? Is it MAX torque or it's related with 2500rpm?

If I simply estimate:
Horsepower = (295 ft lbs x 6000 RPM) / 5252 I get 337 hp at 6000 RPM which could be truth for the rwhp, but not for the crank hp, so I am a bit confused, I guess I am missing something..

I calculated 295.19 ft lbs as a result of power from the engine (not torque at crank). The diagram in the presentation is just to get an understanding of how I calculated the torque (based on rear wheels), from the rear wheels back through rear diff, back through trans, and finally as torque resulting from engine. This value is mainly useful for calculating the horsepower of the engine, and does not reflect how much torque the engine is actually creating.

Earlier in the thread I had mentioned drivetrain loss which I estimated to be around ~%15. When you estimated hp using "(295 ft lbs x 6000 RPM) / 5252 = 337 hp", you were using the torque produced at 2500 rpm. There would be significantly more torque at 6000 rpm.

[rvadim76]

Originally Posted by Dooder

I calculated 295.19 ft lbs as a result of power from the engine (not torque at crank). The diagram in the presentation is just to get an understanding of how I calculated the torque (based on rear wheels), from the rear wheels back through rear diff, back through trans, and finally as torque resulting from engine. This value is mainly useful for calculating the horsepower of the engine, and does not reflect how much torque the engine is actually creating.

Earlier in the thread I had mentioned drivetrain loss which I estimated to be around ~%15. When you estimated hp using "(295 ft lbs x 6000 RPM) / 5252 = 337 hp", you were using the torque produced at 2500 rpm. There would be significantly more torque at 6000 rpm.

OK got it. Pls keep us updated I will be waiting for 4-6K rpm results

Thank you!