I believe we start the HP guage out at 20% driveline
friction, which is kinda the old standby number.
Anecdotally, I've seen that most "net" numbers on typical
cars measured on chassis dynos come in around 15-18% below
the rated values, once the car is up to snuff. Most cars
start off a bit below where they belong.
The AWD has to add some significant drag I'd think. For
round numbers I'd go towards 25% or so. For frontal area,
don't be too scientific, just measure your car's height and
width and subtract for the space under the car between the
tires. That should get you close.
To be sure your numbers are on, be sure your weight of car
and driver are correct. And of course your testing method
needs to be done properly too. Measure from 0 to the top of
second gear. Short shift first, since we'll be looking at
the performance through all of second for the data. First
gear has too much slip at the tire and the lower speeds make
the multiplications less accurate for HP. Third gear
introduces more aero drag, and besides, the room it takes to
run through the whole RPM band in third is just too much.
So 2nd is the way to go. Make sure you are going straight
on level road. Before you get to really analyzing your
data, be sure to set the end speed on your run to the exact
end speed you reached at the top of second gear. (This will
probably be a very small adjustment as long as you are on
level road, since unlike an autocross run we don't have to
contend with oversteer and understeer.) These procedures
should get you a good accurate number, for your conditions.
No matter how you set your parameters, with or without
driveline friction or aero drag, you should be sure to test
on the same piece of ground and as near the same conditions
as possible to assure that your results are comparable.
--Byron
800-775-9511
FstrMnky wrote:
>
> In the HP gauge what was the default "drivetrain friction" setting? Was it
> 10% or 20%.
>
> Also: anyone have any idea what the "drivetrain friction" setting should be
> for an awd subaru. SUBARU???? yes, that was not a typo. i know some scuby
> drivers use the geez so speak up please. I know the Cd=0.35 but what about
> the frontal area? my HP #'s are way off.
>
> thanks in advance
>
> Johnny
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