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Join Date: Apr 2007
Location: Oslo, Norway
Posts: 11
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915 drivetrain HP loss
How many of the Porschehorses are lost in a 915 ZF limited slip gearbox when running the car on a dyno???
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jahu Oslo Norway |
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10-29-2007, 11:56 AM
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Join Date: Oct 2003
Location: Central Fla
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HP loss
We found going from our engine dyno to a 911 with a 915 with a ltd slip to a dynojet 500 rwhp capacity chasssis dyno it lost 15-17 % on the average.
Mike Bruns JBRacing
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The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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10-29-2007, 12:53 PM
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Location: Oslo, Norway
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Drivetrain power loss
Mike,
Thanks for your reply. I am however not quite sure that I follow you in that a % loss implies that the powertrain loss increases with the HP output of the engine. Is this so??
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jahu Oslo Norway |
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10-29-2007, 01:23 PM
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Location: Central Fla
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Loss
The industry calculates a given loss for lets say transaxle is 17-20 %, an automatic trans and rear end with rwd is a certain %, It is more of a parasitic loss
Mike
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The two most useless things to a driver are the braking distance behind you and nine-tenths of a second ago. |
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10-29-2007, 02:52 PM
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Don't take this as gospel, but I think that the actual powertrain loss is calculated from the "run-down" phase after measuring peak HP, believe it's from the time it take to run down the rollers again, but i'm not sure...
A freshly rebuilt 930 with a 915 (2,000 miles on both) fitted with an Gripper 65/40 LSD and an oil pump/internal spray bar kit measured 234 kW at the wheels, drag output measured 48.5 kW for 282.5 kW at the crank (290.5 kW corrected to DIN 70020, according to the operator). Which, at 18% powertrain loss, is somewhat more than I've often seen quoted for a 915, but the LSD and the oil pump do both take power to run. Just a data point.
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'77 S with '78 930 power and a few other things. |
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10-29-2007, 03:43 PM
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Location: Kailua, Bend, & Tamarack
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Why would an LSD make any difference in a dyno test, in which there is no differential action?
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10-29-2007, 04:21 PM
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Location: US
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Although arguably small, the added mass of an LSD will reduce the ultimate power output of the motor, measured at the wheels. Energy is required to increase the rotational velocity of the LSD.
I think this is likely nominal compared w/ the rest of the power train mass. |
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10-29-2007, 06:38 PM
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