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

[Ian Duff]

So you're saying that to compare drivetrain loss between different cars
(Trans Am 455 SD vs Honda Civic), percentage is OK, but on the same car (my
stock 95.5 S6 vs the Happermobile), it could be expressed as HP loss, and
constant, regardless of state of tune? That makes me feel better.
-Ian Duff.
-----Original Message-----
From: Calvin & Diana Craig [mailto:calvinlc at earthlink.net]
Sent: Wednesday, 30 April, 2003 12:34 AM
To: iduff at rcn.com; 'Joseph Pizzimenti'; 'Cody Payne'; ''S-Car-List
(E-mail)'
Subject: RE: [s-cars] Accurate Drive-Train Loss on UrS?



>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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