OK guys, as I mentioned in a previous thread on the G-Tech Pro, I had an idea of how to callibrate out, or correct for the aerodynamic and rolling resistance losses. I tried it out using my Pathfinder (forgive me, please) and it seems to work. I'd be interested in hearing what you guys think.
Basically, I back out these losses by pushing in the clutch and coasting at the end of the HP pull. Upon doing so, there will be a negative acceleration as a result of aerodynamic drag and rolling resistance at this particular speed. Obviously, you'd have to redo the callibration for your individual car. Since the G-tech doesn't print out negative HP, you have to calculate it from the recorded acceleration in G's, (which it does measure). HP = 1.4666*w*G*v/550, which comes by taking the time derivative of the kinetic energy of a moving mass, KE = 1/2mv^2. I can also be done from first principles (def of work and Newton's 2nd law), but this is a simpler starting point. I assume aerodynamic loss goes in proportion to speed to the third power, (which I don't have a reference for, off hand, but that's how it scales.)
Most of the details are in the attached pictures. I will answer questions, however.
Edit: Here was the original thread where this came up.
http://www.svtperformance.com/forum...19&perpage=25&highlight=momentum&pagenumber=2
Some other comments on assumptions. I'm assuming any rolling resistance also goes a speed to the third power, as does the aerodynamic drag. I may be neglecting other parasitic losses that change when the clutch is pushed in. Also, I didn't do any hard shifts to avoid that G-shock that might come in to play.
Basically, I back out these losses by pushing in the clutch and coasting at the end of the HP pull. Upon doing so, there will be a negative acceleration as a result of aerodynamic drag and rolling resistance at this particular speed. Obviously, you'd have to redo the callibration for your individual car. Since the G-tech doesn't print out negative HP, you have to calculate it from the recorded acceleration in G's, (which it does measure). HP = 1.4666*w*G*v/550, which comes by taking the time derivative of the kinetic energy of a moving mass, KE = 1/2mv^2. I can also be done from first principles (def of work and Newton's 2nd law), but this is a simpler starting point. I assume aerodynamic loss goes in proportion to speed to the third power, (which I don't have a reference for, off hand, but that's how it scales.)
Most of the details are in the attached pictures. I will answer questions, however.
Edit: Here was the original thread where this came up.
http://www.svtperformance.com/forum...19&perpage=25&highlight=momentum&pagenumber=2
Some other comments on assumptions. I'm assuming any rolling resistance also goes a speed to the third power, as does the aerodynamic drag. I may be neglecting other parasitic losses that change when the clutch is pushed in. Also, I didn't do any hard shifts to avoid that G-shock that might come in to play.
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