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

[Robert Myers]

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[ Picked text/plain from multipart/alternative ]

Ian,

As power applied to the road increases internal forces inside the
engine/drive train also increase.  This, in turn, increases internal
friction which increases power loss in proportion.

Remember from your HS physics class days: frictional force = force normal
(perpendicular) to the surface multiplied by the coefficient of
friction.  We attempt to manipulate (minimize) the coefficient of friction
by using a lubricant (oil) but we can't completely eliminate friction nor
can we do anything about the internal forces between surfaces.  Those
forces increase as power increases in an exact (and more or less constant)
proportion (if you double the "push" of one gear on a second one you also
double the frictional forces operating between those two gears).  Therefore
frictional losses also increase as power output increases and drive train
loss is fairly closely directly proportional to power output.  It is
convenient to express that as a percentage of produced power.

Does this make sense?

At 08:56 AM 4/30/2003 -0400, Ian Duff wrote:

>Amusement and gaining knowledge is why I'm pursuing this, not to say "I have
>a 400HP car", because I don't. If I were as crazy as some, I wouldn't be
>driving a stock S-car, now would I? I'm more interested in WHY driveline
>loss is expressed as a percentage rather than WHAT that percentage ought to
>be. Your "what" observations are surely accurate, but don't answer my
>original question.
>-Ian Duff.
>-----Original Message-----
>From: QSHIPQ at aol.com [mailto:QSHIPQ at aol.com]
>Sent: Wednesday, 30 April, 2003 7:57 AM
>To: calvinlc at earthlink.net; iduff at rcn.com; pizzoman at yahoo.com;
>Cody.Payne at bconnected.com; s-car-list at audifans.com
>Subject: Re: [s-cars] Accurate Drive-Train Loss on UrS?
>
>
>Some of us older gear heads don't really care what's at the crank, it's what
>gets to the ground that counts.  The best method to confirm "driveline" loss
>is to get the RWHP, estimate, then get a quarter mile time.  With any HP
>figgr you come to, it either results in a faster car or a slower car.  A guy
>can get a faster car matching gears to his HP/Torque curves, than the one
>bolting on parts to the motor, BTST many times.
>
>Specific to the below, the real interest is peak HP and torque values.  As
>such you really only need to figure DLL for those peaks.  In terms of S cars
>on the awd dyno, the accepted figgr is between 25-30%DLL  crank to wheel.
>The torsen cars actually give the least accurate HP figgrs anyhow, since the
>torque shifts fore aft on the rollers .
>
>Remember guys, ANYONE who quotes flywheel HP, unless put on an engine dyno,
>is giving an extrapolated HP figgr.  Looking around to other published
>numbers, rwd/fwd hit around 13-15%, awd hits around double that.  Without
>doing all the math, that sounds pretty reasonable to me.
>
>Right now the best comparo IMO for quattro, is the RWHP figgr, since that's
>the most common to see.  For the turbo I5, you hit 300hp on the chassis
>dyno, you are at least 400 at the crank.  401 or 425?  Who cares?  But the
>guy hitting 383 at the wheels is closer to 500hp at the crank than you are
>with 300 at the wheels.
>
>These discussions can be found dating back decades.  Awd or S car, sure
>doesn't change the amusement gained from them.
>
>SJ
>In a message dated 4/29/2003 11:56:27 PM Central Daylight Time,
>calvinlc at earthlink.net writes:
>
> >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?
>
>Two points here:
>1) Inertia does factor in.  Torque = I * Angular Acceleration.  Since HP =
>Torque*RPM/5252 the higher the I, the more torque it robs.
>2) However, I am along with you for the fact that the percentage is a rotten
>way to say it.  It is a parasitic loss that is going to be dependent upon
>Drivetrain Inertias, as well as RPM for the frictional losses.
>
>I believe the reason you see things expressed in percentages is because in
>general the larger the HP &Torque output the beefier the drivetrain needs
>to be; example would be the clutch/flywheel on my '72 Pontiac vs. a Honda
>Civic.  HUGE difference.  Now, if you keep the drivetrain components the
>same, and then do stuff like better exhaust, more boost, etc. then the
>losses should go down as a percentage.  Also, this will depend alot upon how
>brute force oriented the manufacturer is to solving problems.  Example would
>be using a larger gear in the tranny with thicker teeth as opposed to using
>a higher strength material in the gear and keeping it small.
>
>--Calvin
>
>
>
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____

I've been wondering...  Who would Jesus bomb?

Bob
*****
  Robert L. Myers  304-574-2372
  Rt. 4, Box 57,  Fayetteville, WV 25840 USA  WV tag Q SHIP
  '95 urS6 Cashmere Grey - der Wunderwagen   ICQ 22170244
  http://www.cob-net.org/church/pvcob.htm
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