hp calculation ?

[nize]

i've found a lot of hp calculators based on quarter mile times, trap speeds, and even a very good one based on known torque values;
http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est_intro.html

i'm wondering if there's a way to calculate hp and/or torque based on the following info;
time from 2krpm to 6krpm in fourth gear

anybody know?

[Lawrence Coppari]

You can determine the average horsepower over the range of speed change (linear movement of vehicle) relatively easily. However, you lose all the power that went into making all the rotating parts go faster as well as windage losses.

For a quick calculation you can compute the change in kinetic energy between the two speeds. That change divided by the time that was taken to do it represents the power that reached the pavement minus the energy losses due to air resistance. For the latter you'd have to know the drag coefficient of the vehicle and the frontal area of the vehicle plusthe density of the air. For the rotating parts, you'd have to know moments of inertia of every rotating part in addition to the rotational velocity
changes. There is kinetic energy associated with rotation as well as with linear motion. The inertia stuff is too complicated to do here. Moments of inertia are highly geometry dependent.

But neglecting the air-rotation business you can say (in US units).

Change in kinetic energy = 0.5*m*(vf**2-vi**2) where m is the mass of the car which is the total weight of the vehicle divided by 32.2. Vf and vi are the final and initial velocities of the car in feet/second, respectively. The **2 means squared.

The units of the above are foot pounds. Dividing by seconds gives you ft-lbs/sec, the unit of power. One hp is 550 ft-lbs/sec. Here's a sample calculation.

Car accelerates from 70 to 100 mph in 4 seconds. It weighs 3100 pounds with you in it.

DKE = 0.5 * 3100/32.2 * (146.7**2 - 102.7**2) = 5.281d+05 ft-lbs.

Power = DKE/time = 5.281D+05/(4.0 * 550) = 240 hp

Thus you put an average of 240 hp into the change of speed if you did it in 4 seconds.

There probably is a correction factor that can be applied to account for the losses of spin up rotating parts and power lost to drag of the vehicle. But this is a start.

[pozican]

Nize -- Do this after the dyno day -- Then tweak a final coeffecient to multiply your answer to, in order to get your times to match your dyno times.

Lawrence's example used 70-100.

On the dyno do that -- Plus one more (60-90?)
Then when you try to do your street dyno, you can do the same thing, with the dyno calibration number, and see how close you get.

[nize]

lawrence, that is excellent. thank you.

i am going to try to make an excel spreadsheet to plot the various sections (20-40, 40-60, 60-80, 80-100, 100-120) and then use that info to make a 'street hp' graph. once i have that, i can also make a matching tq graph.

then i can get some more use out of this standalone system;

[ae1969]

Great info lawrence!

You were paying attention in physics. hehehehe

[speedracing944]

Man, my spring break just started. I don't want to look at that stuff during my time off

Speedy