[DeTomaso] Flywheel and damper recommendation

[Daniel C Jones]

> Any recommendations for flywheel and damper to choose for my build?
> Should I go with a lighter flywheel or heavier?

I went with a lighter aluminum flywheel.  Here's why.  It's not a Ford
351C in a Pantera but the physics still apply.  A while back I ran the
numbers for switching from an iron to aluminum flywheel for my Triumph
TR8.  There are a couple of approaches to doing the math. The rigorous
approach is to calculate the polar moment of inertia for the two
different flywheels, adjust for the square of the overall gearing
(transmission, final drive and tires) and convert to an equivalent
linear inertia.  The second method (the one I chose) is to start with
a known linear to rotational equivalent and ratio from there.  The
known relationship I used is a solid disk rolling on its edge.  It has
an effective inertia exactly 1.5 times what it would be if it wasn't
rotating.  That means the rotational component is 50% of the linear
component.  Adjust for the square in gearing and you have the answer.
I wrote a little Fortran program to do the calculations.  I assumed
a 12" diameter flywheel which is the Buick/Rover diameter, less the ring
gear.  The circumerence of a circle is the diameter multiplied by pi.
So if you roll the flywheel along the ground it will move 37.7 linear
inches per revolution (= pi * 12).  A 205/50/15 has a diameter of
approximately 23.1 inches.  My TR8's final drive ratio is 3.45:1 and
first gear is 3.32:1 so one revolution of the flywheel results in the
car moving around 6.3 inches.  Ratio the squares and take half
((37.7/6.3)**2)/2 = 17.9.  So each pound removed from the flywheel
(equally across the face) is the same as about 18 pounds of weight
removed from the car when in first gear.  So if you remove ten pounds
from the flywheel (equally across the face), the result is equivalent
to removing 180 pounds of vehicle weight in first gear.  The effect
goes down for each higher gear, of course.   Removing weight farther
from the rotational axis has a more pronounced effect.  If the weight
is removed from the outside of the flywheel only, the effect is about
2.78 times as strong since a solid disk has a radius of gyration of
0.6 times the radius (1.0/0.6)**2 is 2.78).  2.78 * 180 is 500 lbs
equivalent weight reduction.  A non-trivial effect, particularly
in a lightweight car.  I ran the numbers a couple of ways to
illustrate.  For my TR8, assuming a 3.45:1 final drive ratio,
205/50/15 tires and LT77 gear ratios of:

 1st 3.32:1
 2nd 2.09:1
 3rd 1.40:1
 4th 1.00:1
 5th 0.83:1

along with flywheel weights of:

 stock flywheel - 32 lbs
 lightened steel - 22 lbs
 aluminum - 11 lbs

The engine in the TR8 is essentially a Buick 215 aluminum V8 from the
early 1960's.  The stock flywheels in those had a big ring around the
perimeter.  Lightening the flywheel by milling off the ring is similar
to removing the mass from the perimeter (from 32 to 22 lbs).  In the
numbers below, I didn't do it that way but a more accurate approach for
the aluminum flywheel would be to assume a reduction of 22 to 11 lbs
equally across the face and add that to the difference of the 32 to
22 lbs across the perimeter.  In any event, a lighter flywheel looks
like a good thing to do for performance.  Here are the numbers:

 32 to 22 lbs (across face assumption):
 1st 177.5 lbs
 2nd  70.3 lbs
 3rd  31.6 lbs
 4th  16.1 lbs
 5th  11.1 lbs

 32 to 22 lbs (perimeter reduction assumption):
 1st 493.4 lbs
 2nd 195.5 lbs
 3rd  87.7 lbs
 4th  44.8 lbs
 5th  30.8 lbs

 32 to 11 lbs (across face assumption):
 1st  372.7 lbs
 2nd  147.7 lbs
 3rd   66.3 lbs
 4th   33.8 lbs
 5th   23.3 lbs

 32 to 11 lbs (perimeter reduction assumption):
 1st  1036.1 lbs
 2nd   410.6 lbs
 3rd   184.2 lbs
 4th    94.0 lbs
 5th    64.8 lbs

Rotational inertia is mass multiplied by the distance from the
rotational axis (integrated over the surface).  The effect is
stronger farther away from the hub.  The best is from the
perimeter.  Equally across the face is less effective and near
the hub is the least effective.  In my example, dropping 21 lbs
from the perimeter is equivalent to over 1000 lbs reduction in
weight in first gear.  Dropping the same mass the face is equivalent
to 372.7 lbs.

Reducing the flywheel inertia does reduce the stored energy for
start from a stop.  Torque follows displacement.  Little engine
in big car with tall gearing needs more stored inertia at start.
Big engine in little car with short gearing can get away with
much less stored inertia.  On the street with a ligter flywheel,
you may need to use more RPM and clutch slip.  On the strip, you
may bog if you don't have enough excess torque at the rear tires
(more traction than engine/gearing).  Remember that HP is the
measure of how much potential torque you can have at the rear
tires via gearing.  If you have enough power to overcome your
traction, then a heavy flywheel is a loser.

> I used the Fluidyne FLU-650211 damper

I'm not a fan of the Fluidyne damper.  Here's why.  There are three basic
types of harmonic dampers:

 1. Elastomer
 2. Lanchester
 3. Visous Fluid

OEM automobile applications use elastomer-style dampers.  Construction
consists of an outer inertia ring with rubber insulator that is bonded
or pressed onto an inner crank hub.  The ring on the rubber is tuned to
a particular frequency.  Essentially, an additional mass is elastically
bonded to the primary mass. Since the natural frequency of the additional
mass is constant, it is only effective when the crankshaft frequency is
within the range of the damper mass tuned frequency.  It modifies the
vibration present (i.e. they don't tune out any particular frequency but rather
clip the peaks off the harmonics).  They are effective at damping torsional
vibrations in a crankshaft but they work best in engines that see relatively
modest angular accelerations.  They are well suited to engines that see heavy
loads at constant or slowly varying RPM and are commonly used in diesel truck,
marine and locomotive applications.  However, on a road race engine that sees
constantly changing RPM (with high rates of change), the viscous damper lags
behind the RPM change which heats up the silicone fluid.  You can thing of a
ring in viscous fluid as a damper like a shock absorber and it will overheat
if used continuously.  Also, the silicone fluid will, after constant heat
absorption during its service life, reduce in viscosity value.  Some industrial
dampers have sampling plugs fitted into the housing that allow fluid to be
extracted for analysis.  Metaldyne recommends overhaul when the fluid has
reduced 50% in viscosity value.  At that stage, the damping efficiency will
be 80% of the original.

The Lanchester damper is a pendulum style invented by aviation pioneer
Frederick W. Lanchester 100 years or so ago.  It works at all RPM as the
centrifugal force field changes the natural frequency of the pendulum as
rpm increases (the natural frequency of the centrifugal pendulum absorber
is directly proportional to the angular velocity of the primary structure).
In theory, the Lanchester damper should be a good match for a stroker engine
but the published results I've seen were not particularly impressive.
The TCI Rattler is a pendulum style damper.  TCI did an SAE paper on their
Rattler damper but the results didn't look any better than a conventional
damper.

All the serious race teams I'm aware of use elastomer balancers but some
of the teams have the resources to have them tuned to their specific engines.
Perhaps some of the engine builders can jump in here but I've been told
BHJ, Powerbond (Pioneer), FRPP, Innovators West and Romac are good quality
parts.  ATI is as well but pricey.  Pro Form, Engine Works and TCI should
be avoided.

Dan Jones