Horsepower loss in drive train
Wed, 24 Jul 2002 07:50:32 -0600
Sense or nonsense, I know the Dynapack folks are pretty adamant in ascribing
and suggesting the application of a 25% "TCF" (which I believe stands for
Transmission Correction Factor) to all quattro drivelines! The factor is
applied to the bhp & torque numbers their dyno system measures at the wheels
to "calculate" flywheel figures. I think their systems math is set up
something like, "OK, so you measured 100 bhp at the wheels, applying a 25%
correction factor (100 x 1.25), that means you've got something like 125 SAE
bhp at the engine or flywheel. I was told the 25% TCF is based on many
years of experience & "1000's of test runs by Dyanpack on different Audi
Regardless of the "TCF" factor you select, a refinement on what I think
you've suggested and pointed out, that I have particular difficulty with, is
in understanding the claim that this figure is applied regardless of whether
the engine in question is generating 100, or 200 or 300+bhp!
In other words you have the same chassis, say an Audi 100/A6 Quattro, but
out fitted with three different motors:
Car A a NA 2.2 liter inline 5 cylinder of (??) factory spec'd @ 130 bhp;
Car B a stock UrS4/6 making per the factory numbers @ 227 bhp 5 cyl turbo;
Car C a tweaked RS2 spec UrS4/6 pushing, depending on your tuner's claims
anything from @280 to 420 bhp
same drivelines (well more or less.) If Dynapack's correct, and one is to
apply the same TCF across the board to all three vehicles, why is, or better
yet where is the additional 70 to 80 hp Car C's chassis vs. say Car A, is
sucking off the motor going? Is there that much power being sucked up by
the turbo to account for the difference? Does an additional 290 bhp
(420-130) really generate an additional, what 58 to 60 hp in internal engine
or transmission friction and other power losses?
Date: Tue, 23 Jul 2002 14:51:57
From: Mike Arman <email@example.com>
Subject: Horsepower loss in drive train
I have to question the statement that there are large HP losses in the
drive train - one previous post mentioned a 70 HP loss, I think in a 914.
70 HP is 750 watts times 70, or 52,500 watts (52KW), which is enough to
light up your house and your central A/C for several hours.
70 HP is 33,000 foot pounds of work per minute times 70, or 2,310,000
ft/lbs of energy, which is enough to lift one ton 1,155 feet into the air
in one minute.
70 HP is lotsa BTU's, somewhere I have the conversion, but I'll bet it
comes out HOT!
I forget what the other conversions are, but the point is, this energy has
to GO SOMEPLACE - it has to come out as light, heat, noise, something! It
cannot simply evaporate into thin air.
The statement "lost in the drive train" makes no sense.
I think what is happening is the engine is putting out XXX horsepower when
mounted on a test stand, no accessories, perfect cooling and mixture, cold
air in, no exhaust restrictions or smog controls on the way out, basically
under absolutely ideal, no load whatsoever conditions.
When we put it back into the car, we add an air filter, mufflers, smog
devices, alternator, water pump, cooling fan, transmission, blah blah blah,
and then, yes, we get much less horsepower where the tires sit on the
I also wonder what effect the advertising department and/or wishful
thinking has on absolute power output (wasn't yellow powder coat good for
"N" horsepower per square inch of item thus treated?).