my dyno sheets from today (and a quick question)
07-07-2002 | 11:35 AM
#12
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Joined: Jun 2002
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QUOTE
Cheuk in Seoul:
The run down test is not bad but it still will not account for all the drivetrain / frictional losses.
I use a standard of 15% for manual trannies... I think that most will agree with this number for Dynojets.
Why wouldn't it?The run down test is not bad but it still will not account for all the drivetrain / frictional losses.
I use a standard of 15% for manual trannies... I think that most will agree with this number for Dynojets.
The internall friction generated from a run down test includes your CV joints and all the gears, which are rotating when in neutral, only with the clutch depressed are the gears not moving.
07-07-2002 | 12:29 PM
#13
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Joined: Nov 2001
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I forgot exactly why... it's been a while since I looked at the Dynojet manual. I think it has to do with a couple of things. First the losses are different depending on if the drivetrain is under load or not. Also if the negative hp run is made with the car in neutral, the gears are not being driven, so all the frictional losses from the gears being driven are not accounted for. It's been a long time since I did a negative hp run but I think I did it with the clutch depressed but with the tranny still in 4th gear. All in all the negative hp runs become guestimates... pretty close but still an approximate number. We usually tell the customer who makes wants a negative hp run that the number is the mimimum hp that is lost in the drivetrain.
Most people try not to muddy up the picture by sticking to hp at the wheels... because that is what counts.
I should add that with the clutch depressed you disengage the drivetrain from the flywheel. When you put a car in neutral you disengage the transmission. So for an accurate drivetrain loss test, the clutch should be pressed in and the transmission should remain in gear... spinning with the tires / differential.
Most people try not to muddy up the picture by sticking to hp at the wheels... because that is what counts.
I should add that with the clutch depressed you disengage the drivetrain from the flywheel. When you put a car in neutral you disengage the transmission. So for an accurate drivetrain loss test, the clutch should be pressed in and the transmission should remain in gear... spinning with the tires / differential.
07-08-2002 | 02:02 AM
#14
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Makes sense that the internal friction should be higher with load, but all modern gearboxes are constant mesh gear boxes, so the gears are always rotating except when your at a stop and the clutch is depressed.
But a run down test is still the most accurate way to know what the internal friction is outside of dynoing at the wheels and then pulling the motor and dynoing at the flywheel...and I really don't think anyone here really wants to do this tongue.gif
But a run down test is still the most accurate way to know what the internal friction is outside of dynoing at the wheels and then pulling the motor and dynoing at the flywheel...and I really don't think anyone here really wants to do this tongue.gif