[s-cars] Accurate Drive-Train Loss on UrS?

[Ian Duff]

Shouldn't a dyno be able to measure drivetrain loss? Run the drivetrain up
to some predetermined rate, then put the clutch in. The dyno should be able
to load the driveline down until it's at rest, and to measure how much power
it is extracting to spin it down.

My question is, will the dyno be measuring the HP needed to spin the
driveline at each driveline RPM point, or will it be measuring the friction
the driveline induces, as a percentage?

Every discussion I've heard about driveline loss is expressed as a
percentage, i.e. frictional. If this is the case, those losses must be
delivered as heat. If this is the case, why don't we hear of tuned high HP
cars having lube problems in the transmission or diff?

Conversely, why should the driveline require more power to be spun when
connected to a tuned motor, as opposed to a more pedestrian stock motor? It
would seem to me that to spin the halfshafts at 60 or even 200 RPM would
take the same effort, regardless of what HP the engine was capable of
putting out. Rotational inertia does not factor in here, as HP is a steady
state measurement, is it not?

I would think we should be able to get a dyno chart for our driveline, HP
and torque, with at the wheel rotational speed reported, rather than engine
RPM. Be a great way to measure gearbox oil effectiveness <g>.

What am I missing? Help me out here, you Ivory Tower Gurus of Automotive
Theory.

-Ian Duff.
-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of Joseph Pizzimenti
Sent: Tuesday, 29 April, 2003 3:29 PM
To: Cody Payne; 'S-Car-List (E-mail)
Subject: Re: [s-cars] Accurate Drive-Train Loss on UrS?


Cody,
Don't live by the numbers, you'll drive yourself
crazy.  Dyno numbers vary with altitude, correction
factor, ambient temps, what the dyno operator had for
breakfast, blah, blah, blah...

Who really cares if it's 380 or 396?  If you put down
317 to the ground, not much else matters.  As long as
you have fun with it and love driving it, who the f***
cares?

But FWIW, upon talking with a hub dyno operator round
these parts, he goes by 25% drivetrain loss.  Others
say 20%  But whatever makes you happy, man.

Joe
--- Cody Payne <Cody.Payne at bconnected.com> wrote:
> Gents,
> 	What would be an estimate of the average Quattro
> drive train HP loss on our UrS's?  20%? 25%? Other?
>
> I am shooting for around 400HP at the crank,
> including a FMIC and don't want to short myself with
> incorrect configuration..yet not go overboard and
> have to update my Piston connecting rods and Head
> this time around.
> 	I know that with a full RS2 conversion with the
> addition of a FMIC and proper software the UrS can
> dyno at around 317 at the wheels...add 20% equals
> 380 at the crank.  25% equals 396HP which would be
> plenty close for me w/ fully proven RS2 components.
>
> Cheers
>
> cp
> _______________________________________________
> S-CAR-List mailing list
> S-CAR-List at audifans.com
> http://www.audifans.com/mailman/listinfo/s-car-list


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