[DeTomaso] Flywheel and damper recommendation
adin at frontier.net
adin at frontier.net
Wed Jan 16 12:07:37 EST 2008
Many of us use method #1 - even down to the "do I need a chrome
dipstick" type questions.
IF you find yourself in this group, I hope you sent Dan (Dan's Dyno
Interpretation Services) a little something -beer, a fat check, nice
christmas car - to help pay for our coming dyno tests. Its only fair.
grouchy and dirty in durango, chair of the "keep our resources happy"
committee.
Quoting Larry - Ohio Time Corp <larry at ohiotimecorp.com>:
> To All,
>
> I came to the very same conclusion to use an aluminum flywheel in a much
> EZer method.
>
> 1. I asked Dan first.
> 2. It was shinie
> 3. Ken Green got us a good deal on them.
>
>
> Larry (dumb as a rock) - Cleveland
>
>
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
> Behalf Of Daniel C Jones
> Sent: Wednesday, January 16, 2008 11:20 AM
> To: charles buthala
> Cc: detomaso at realbig.com
> Subject: Re: [DeTomaso] Flywheel and damper recommendation
>
>> 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
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