Gary Z

I never said there would be no effect. To illustrate my main point, suppose you have a monster crank pulley that weighs 20 pounds and a diameter of 7 inches. Also suppose that you have a lightweight bicycle wheel that only weighs 2 pounds and a typical diameter of 26 inches. Which has the higher rotational inertia? The effective radius of the bicycle wheel is very near 26 divided by 2 = 13 because most of the mass of the wheel is concentrated near the rim. A fair approximation is about 12 inches. Similarly, the effective radius of the pulley is less than 7 divided by 2 = 3.5 A generous approximation is 3 inches.

It is not necessary to worry about units like kilogram-meters-squared because different units will not change which is larger. We only need to be consistent and use the same units in all calculations. We can stay with pounds and inches.

Mass times radius squared is:

Pulley: 20 *3* 3 = 180

Bicycle Wheel: 2 *12 * 12 = 288

So we can see that the rotational inertia of a big, heavy pulley is less than a lightweight bicycle wheel. And remember, this is the entire pulley, not just the A/C groves.

The effective radius of a flywheel/clutch-pressure-plate or a flexplate/torque-converter is very difficult to estimate because of the complex shapes. We can agree that both the mass and radius are greater for the flywheel than for the pulley. Suppose for approximation we say 40 pounds and 4 inches. In our simple units the rotational inertia is:

Flywheel/clutch: 40*4*4 = 640

Compare this to the inertia of the pulley groves alone:

Pulley Groves: 4*3*3 = 36

Removing the A/C pulley groves (I serously question 4 pounds) would reduce the total rotational inertia of the flywheel/torque-converter/pulley combination by some amount near five percent at most. This small change will not measureably reduce your quarter-mile elapsed-time or noticeably improve the sound of your engine when you blip the throttle.

You are correct that any weight removed helps. And Damian is right - it is a bad idea to modify a damper pulley.

Mighty Whitey

Well put! The fywheel/converter weight makes More sense As to why a car with a 10" converter responds much better, than one with a stock 12" unit.

Again, I never personally seen a before and after result between the stock balancer and the modified one in regards to the motor revving "quicker", just taking the testimony of what the owner said to me.

In regards to the material removal being a major issue with harmonic dampening abilities strictly because of the wright being gone, a simIlar statement could be made for any aftermarket dampener?

I can see this being an issue with a stock, unbalanced motor, given the fact that they are relatively out of balance from the factory, but a fresh shortblock that has been balanced should have very little harmonic vibration, correct?

Lol, this reminds me of the countless number or lt1's I've worked on over the years, where the owners have bought under drive pulleys that sandwhich between the hub and stock dampener, and thought the new piece replaced the old dampener all together. Then they wonder why their bottom end is shot afte only a couple months...

joecar

Harmonic's occur regardless of how well/precisely a crank is balanced...

the crank twists/untwists with each ignition event... at some particular rpm's (dependent on rotating mass/dimensions) the twist/untwist action starts to resonate (i.e. the oscillation self-excites) and becomes bigger (i.e. the crank has two superimposed motions: angular rotation and angular oscillation... similar to DC+AC)... the harmonic damper moves the resonant frequency's/rpm's to a different range so that they will never be hit (i.e. the harmonic's are dampened).

StanIROCZ

I just found this tread during a search - was wondering how much lighter an LS6 corvette balancer is versus an F-car LS1....

But a comment on this topic; dampers are a tuned mass system that are usually tuned to resonate or absorb energy at a certain frequency. That frequency is effected by the amount of mass, the stiffness of the spring (rubber elastomer in this case), and the damping (inefficency in the rubber).

So if you take 4 lbs off the inertia ring of the balancer the frequency that the damper functions at is going to increase - and I'm not sure that is a good thing because your crankshaft (etc) is still going to have its bad resonances at the same speed and you didn't lower the stiffness of the rubber to bring that frequency back down.

The ability to damp out undesireable resonaces is related to the mass of the inertia ring. So if you remove mass from the ring, it is also going to be less effective at damping. Inertia is inertia in this case - it is a necessary evil to protect your engine from damage.

So the short of it is hillbilly mass reduction of a balancer is not a good thing unless there is some significant engineering to correct for the changes you made in frequency, and even then that cannot counter act the ineritia that you took out that is necessary for the damper to do its job.

Now if we are talking about the hub (area inside the rubber ring) that is a different story. You can reduce its weight without drastically effecting the system.