Spool and lag discussion
02-21-2008, 11:59 AM
#22
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The curve of that P-drag plot is dependent on RPM not HP
If there was a connection between the amount of power being transfered and P-drag the curve for P-drag would change at just above 5600 RPM where all the power curves flatten out. The curve is a nice smooth parabola that indicates it is only related to RPM.
I should have stated in the original post that the losses will vary with RPM, but not with power.
That 217hp drag estimate is at 7800rpm. At 5000 rpm the drag is just above 80hp.
That P-drag plot is useful as an estimate for comparing peak hp numbers at different RPM, but the only way to really know the losses is to run the engine on an engine dyno then on a chassis dyno and overlay the plots. The difference between the two will be the drivetrain loss. Losses will vary with RPM but not with power.
I should have stated in the original post that the losses will vary with RPM, but not with power.
That 217hp drag estimate is at 7800rpm. At 5000 rpm the drag is just above 80hp.
That P-drag plot is useful as an estimate for comparing peak hp numbers at different RPM, but the only way to really know the losses is to run the engine on an engine dyno then on a chassis dyno and overlay the plots. The difference between the two will be the drivetrain loss. Losses will vary with RPM but not with power.
02-21-2008, 12:05 PM
#23
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So, based on that you're saying a stock car makes only 30hp at the wheels at 7k?
Run a 7a Coupe motor to 7500RPM and you'll see a hell of a lot less drag.
160hp to start with, and it can certainly rev to 7500 loaded up on a dyno, which if things were only RPM based would mean they'd grind to a halt at that speed with the fixed drag you're proclaiming..
More power = more gear face/bearing load = more friction = heat = energy used to make that heat = less power at the wheels.
160hp to start with, and it can certainly rev to 7500 loaded up on a dyno, which if things were only RPM based would mean they'd grind to a halt at that speed with the fixed drag you're proclaiming..
More power = more gear face/bearing load = more friction = heat = energy used to make that heat = less power at the wheels.
02-21-2008, 12:18 PM
#24
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I'm not saying it. Your graph is.
If a variable that affects P-drag changes the curve for P-drag must change as well. The curve does not change at 5600rpm when the power curves change so P-drag can't be related to HP.
The P-drag being calculated by the dyno software may be incorrect. It may be estimating losses that are too high.
The P-drag being calculated by the dyno software may be incorrect. It may be estimating losses that are too high.
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