Quote:
Originally Posted by 8cd03gro
Loss to heat as a percentage of power output decreases as power increases because inertia of the drivetrain and friction remain the same regardless of power output. This does not mean loss is a constant because some forces are variable, but the impact of constant forces become less apparent as power increases. These are just hypothetical and in no way accurate as it leaves out a loooottt of variables, but as an example
Let's say I is the force required to overcome the inertia of the drivetrain, it is a constant. Y is the total power output of the engine and X is the power at the wheels. Just for simplicity we will assume a 12% loss due to variables other than inertia. In this oversimplified example the function of total power output to determine wheel hp would be
X = 0.88Y-I
As Y increases, I remains the same. So, let's say I is 10hp, and Y is 400hp.
X = 0.88(400)-10
X = 342 or 85.5% of crank horsepower.
Now we'll increase crank output to 500
X = 0.88(500)-10
X = 430 or 86% of crank horsepower.
Now, again this is massively oversimplified, but you get the idea. Some of the factors that drain hp are constant and some are variable. As you increase power, the constants have less of an impact as far as percentage loss is concerned.
Any engineers, feel free to correct me. My expertise lies in econometrics, not engineering.
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I think your general premise here is correct. It is somewhat simplified but I think sound in principle.
We are also forgetting about the dynos themselves. There is a lot that goes into maintaining and operating a dyno properly. I have little experience with chassis dynos but am involved with a lot of engine testing on engine dynos. Who is to say these chassis dynos are even properly maintained and calibrated. There are so many variables with these chassis dynos. I am very skeptical of them. They are only good for delta comparisons.
The only numbers I really believe are the crankshaft power numbers that come from Ford and GM, in terms of these two cars. Those numbers are correct.