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I need help to figure out how to turn acceleration data into Horsepower/Torqueby soundengineer
Tags: horsepower torque 
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#1
Dec1908, 01:01 PM

P: 33

I have a vehicle with some known info...
weight: 3400lbs Speed at a specific time: see data in chart linked below overall gear ratio: 2.922 Tire size: 25.68 inch Radius RPM at speed: see data in chart linked below heres the data Acceleration Data via Google Documents where do I start?? I dont mind doing math....but I need some help understanding what I need to do and where I need to start. I probably want to do this over a 1 second sample so that I dont have to do any x1000 or /1000 math in there... I can convert the speed into Kph and the mass I can do in kg if it makes it easier I hope to come up with a basic understanding of the math involved and do a little chart of Horsepower and torque vs RPM in the end 


#2
Dec1908, 02:08 PM

P: 539

I tried to a car analysis at one time. Here is a link with a lot of formulas:
http://www.rdrop.com/~/larry/download/formulas.pdf See if this helps. I couldn't see your car data. 


#3
Dec1908, 03:31 PM

P: 33

not really...I can find all of those formulas and I understand them on their own.... its making them work together to get my formula here... I know the mass and I know that it accelerates a certain amount over a given time.... how do I calculate horsepower for that given time... I can set it at 1 second or 10 seconds....I dont care about teh interval...al I want to know is how to get from acceleration of 12mph in one second to horsepower value for that tme 


#4
Dec1908, 04:11 PM

P: 539

I need help to figure out how to turn acceleration data into Horsepower/Torque
Did you try looking for any dyno chart data for your stock vehicle online? This could simplify your task tremendously.
I'll take a better look at your question when time permits. 


#5
Dec1908, 04:19 PM

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P: 41,369




#6
Dec1908, 04:26 PM

P: 539

Acceleration of the car is caused by a force. When the force acts over a certain distance it does work. If you assume that the acceleration is constant, then the force is constant: force = mass x acceleration. When you accelerate your car and it moves over a distance d, work is done: Work = force x distance and has units of joules (energy). Now, it takes your car some amount of time to traverse this distance. Power is the rate at which work is applied: power = work / time and has units of joules per second (or watts). Horsepower conversion: 1 hp = 750 watts (approx.).
Don't forget that the car has to overcome numerous frictional forces so this may complicate your analysis. Does this give you a better idea? 


#7
Dec1908, 04:30 PM

P: 146

I did this for a math experiment to test horsepower of cars and compare them to manufacturers data.
I fitted a curve to the data as a function of time, then used that as position function x(t). from there there are many ways to get to power as a function of time; remember a car's power changes with time (it is not constant). 


#8
Dec1908, 07:09 PM

P: 33

I redid the URL you should be able to see it now....I forgot to put it in share mode 


#9
Dec1908, 07:20 PM

P: 33

I get this...... I just have a hard time with understanding the units force = mass x acceleration what units are force? is mass LBS or KG what is the acceleration unit? so work(joules) = (mass x acceleration) x distance how can I get the distance? tire diameter math and speed correct? and does that need to be in inches? feet? meters? so...Power(watts) =((mass x acceleration) x distance) / time(in seconds?) and that whole thing... watts * 0.00134102209 = Horsepower or watts / 745.699872 = Horsepower am I correct in the math formula?? if yes..then I just need help with the units of measure being used in my variables 


#10
Dec1908, 07:28 PM

P: 3,016

Force should be in Newtons or poundforce. You need to get the mass of your car instead of weight. I would go with metric units for now. Covert your weight to Newtons and then divide by local gravity 9.81 m/s^{2} should be fine.



#11
Dec1908, 07:40 PM

P: 33

3400 * 4.4482216 = 15123.95344 newtons / 9.81 = 1541.6874046890927624872579001019 rounded = 1541.6874 (what unit???) and what about the acceleration part... what formula is my acceleration? and what are my units for acceleration? 


#12
Dec1908, 07:48 PM

P: 3,016

mass=kgs
acceleration should be in meters per second squared. But you do not have acceleration, you have the vehicles speed (or velocity) at various times. You need to come up with a formula or function that relates the sample velocities to time. 


#13
Dec1908, 07:57 PM

P: 33

1 pound = 0.45359237 kilograms (google) and taken 3400lbs * 0.45359237 = 1542.214058 kilograms even though it doesnt quite match up to the previous math 1541.6874 kg? as far as the acceleration... difference in velocity over difference in time ? correct?? this formula just popped back in my head... so (dV2dV1)/(dT2dT2) velocity in meters/second and time in seconds which gives me the acceleration in m/s^2 so...Power(watts) =(([mass_in_kg] x [(dV2dV1)/(dT2dT2)]) x [meters_traveled]) / time(in seconds) 


#14
Dec1908, 08:24 PM

P: 3,016

Looks pretty good to me. (dV2dV1)/(dT2dT2) will get you the average acceleration and hence the average force and hence the average power.
You might be able to get a better approximation of acceleration by plotting a portion of your data in excel and finding a regression line and then using that to find the work done. But, that is only if you want to. 


#15
Dec1908, 08:40 PM

P: 33

I have plans on using the data to solving for horsepower in vehicles at the dragstrip... lets me know if the vehicle is running it tip top shape or if we need to adjust some things to get a little more power out of it.. we know what it does at its best...and we know what to adjust to compensate for various weather/climate conditions to get back to that....we've only figured that stuff out from the dyno....if we can come up with a dyno on the dragstrip then we can run a better race one thing I dont get Power(watts) =(([mass_in_kg] x [(dV2dV1)/(dT2dT2)]) x [meters_traveled]) / time(in seconds) what is my bold type time in seconds? where do I get that value? 


#16
Dec1908, 08:54 PM

P: 3,016

I believe that should be the same time as used in the formula for acceleration. Think about it, you want to know how much Work (Force*displacement) this thing does PER second (Power). So if your force was calculated over a certain time interval (and then work with a corresponding distance interval) than you need to divide that work by THAT time interval to get Power over that interval.



#17
Dec1908, 09:04 PM

P: 33

so a recap to make sure this is right ((([mass_in_kg] x [(dV2dV1)/(dT2dT1)]) x [meters_traveled]) / [(dT2dT1)seconds])* 0.00134102209 = Horsepower Torque = (Horsepower x 5252)/RPM then I can plot them both in excel and do some comparisons :) 


#18
Dec1908, 09:53 PM

P: 33

ok...so I think I did some bad math somewhere...
seconds/rpm/mph/gear/dv/dt/distance/HP 7.52 3551 22.37 2.922 0.62 0.07 0.65 0.83 7.65 3605 22.99 2.922 0.62 0.13 1.34 1.71 obviously my HP math is wrong somewhere =(((3400*0.45359237)*(DV/DT)*Distance)*DT)*0.00134102209 I also reupdated the Data in the google documents page you are looking at data in line 10/11 


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