question on HP and how its measured (LAC)

[Mihnea Cotet]

At 12:16 23/07/2002 -0700, Dupree, Jim wrote:
>Normally the published ratings are crankshaft HP & torque. Most are probably
>calculated and not test stand numbers.
>
>I have been told different thing with regards to hp measured at the wheel. I
>have heard of 15% loss, 25% loss and several different set HP 's loss
>measuring this way. We were told when we dyno'd a 914 track car that there
>was probably about 70hp loss. This is a 3.2L 911 6cyl engine with twin plug
>ignition, carbs and headers. It measures 227HP at the wheels and we were
>told it should be making close to 300 HP at the crank. Is there any standard
>or method for figuring the loss?

I'll have my car ('85 coupe quattro) on a dyno in RWD form on a Bosch dyno
pretty soon and I've already spoken to the shop's owner, who showed me a
dyno graph and told me how everything works. The Bosch dynos measure
power/torque at the wheels and then, after the acceleration, the car has to
decelerate by itself, which translates itself in a negative HP reading.
THAT negative reading is the drivetrain loss actually, and the Bosch dyno
calculates the HP at the crank according to the drivetrain losses. The car
will be dynoed in RWD form because the dyno is a 2WD only so I'll pull the
front driveshafts, use some old outer CV joints to hold the bearings, lock
the center diff and that's all.. of course, this won't ever work on a
Tor$en car...

HTH,


Mihnea