I feel as Mark does in this matter of the "lighter flywheel". Once the
clutch is engaged, the whole drive train becomes part of the flywheel
and the effect of lightening diminishes greatly. At least so far as
acceleration is concerned.
In the case of an inline six, weight reduction of the flywheel helps to
keep it attached to the crankshaft when going thru the harmonic
vibration stage of certain rpm. This, I believe, is the light flywheel's
greatest contribution for race engines.
Dick
From: mhooper@digiscreen.ca(Mark Hooper) 6pack@autox.team.net Subject:
RE: Are stock TR6 engines balance externally- NOW benefit of light
flywheel
Hi Vance:
I understand what you're saying. Angular momentum/inertia and all that
will definitely suck power when accelerating. However, I'm less
convinced on how much help lightening the flywheel will give in
accelerating the vehicle. Ignoring all calculations of any complexity
let's go for a simple common sense analysis and see what we get:
Neglecting all issues related to friction etc, when the car is at any
velocity, its kinetic energy is primarily stored in two areas, the
linear movement of the entire machine and the angular momentum of the
rotating machinery.
The total car weighs about 2800 lbs with driver, gas and essential
toolkit in the boot. The 10 lbs represents about 0.3% of that mass to
accelerate.
If one adds up the crankshaft and its extensions, transmission/diff
gearing, drive shafts, hubs and wheels, the weight must be 500 pounds of
rotating machinery. The transmission changes how much each part has to
accelerate, but not as much as one might think, considering the mass of
the other parts. The 10 lbs removed from the flywheel would represent 2%
of that mass.
So, after lightening the flywheel, in a smooth one-gear acceleration
from zero to 30mph in first gear you would still have the entire car
(-10lbs) and all the rotating mass (-10 lbs) to accelerate. As above,
the savings would be a reduction of about 0.3% of weight to accelerate
linearly and about 2% mass to acceleration angularly. That's just not a
lot of change. Of course, I understand that the gearing between wheels
and motor in first gear would increase the effect, but not all that
much, I would have thought.
Since 10 hp represents about 10% of the power that is actually moving
the car, I find it difficult to believe that lightening the machinery by
so little will have that much of a difference.
So, while I will absolutely buy into the idea that, with the clutch
disengaged, the rotating mass of the engine will be lighter making
revving and matching gears quicker, I'd like to see an actual
acceleration test to be convinced that the overall vehicle acceleration
effect was significant.
Cheers,
Mark
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