Pros/Cons of using aluminum ring harmonic balancer?

[Rick!]

any chance you can educate me on how ATI "tune" a damper?

Typically with encoders on the crank measuring twist.
By varying o ring design, number and durometer, along with diameter for a given application and rpm.

That's the how. The "why" is that every crank has a torsional 1st mode (resonant frequency) somewhere in the operating rpm of the engine and the tuned damper minimizes the angular deflection that happens. The smaller engines I dealt with deflect around 3-6 degrees. Some nitro hemi folks say that the crank deflects around 20 degrees during running which then the cam guy has to account for in the grind.
Cranks are made of stiff pieces (crankpins) and not as stiff pieces, namely the rod pins and pork chops and when put together they will have a spot between the snout and rear flange that is susceptible to twisting. Sometimes the twisting happens near the same time a bending frequency is excited but that's not very often. (A bending mode that lives for any amount of time in a crank is a really bad thing. If you find the thread where the sbf crank broke you can see the beach marks are straight across the fracture which means nearly 100% bending failed it.)
In simple terms, the heavier the balancer and clutch/drivetrain (think inertia), the lower the torsional resonant frequency and vice versa. The "balance" is inserting the resonant frequency where it's only a "pass through" and spends little no time there.

[Warp Speed]

^^^^^ is this done at time of balancing?

On a running engine.

[Warp Speed]

any chance you can educate me on how ATI "tune" a damper?

Typically with encoders on the crank measuring twist.
By varying o ring design, number and durometer, along with diameter for a given application and rpm.

That's the how. The "why" is that every crank has a torsional 1st mode (resonant frequency) somewhere in the operating rpm of the engine and the tuned damper minimizes the angular deflection that happens. The smaller engines I dealt with deflect around 3-6 degrees. Some nitro hemi folks say that the crank deflects around 20 degrees during running which then the cam guy has to account for in the grind.
Cranks are made of stiff pieces (crankpins) and not as stiff pieces, namely the rod pins and pork chops and when put together they will have a spot between the snout and rear flange that is susceptible to twisting. Sometimes the twisting happens near the same time a bending frequency is excited but that's not very often. (A bending mode that lives for any amount of time in a crank is a really bad thing. If you find the thread where the sbf crank broke you can see the beach marks are straight across the fracture which means nearly 100% bending failed it.)
In simple terms, the heavier the balancer and clutch/drivetrain (think inertia), the lower the torsional resonant frequency and vice versa. The "balance" is inserting the resonant frequency where it's only a "pass through" and spends little no time there.

Yep! ^^^^^
Bending can be a bad bad thing, and very hard to accurately measure!

[shoedoos]

sooooooooo.....in the case of ATI.....you buy one of their balancers, you build engine, you put it on dyno, call ATI, they come along and tune their balancer? Or? Do you build engine without balancer, ATI come along while you dyno without said balancer and they measure to tune a balancer afterward?

[modok]

If the rotational mass of the inertia ring is far less than a steel one, then heck no.

Also in most cases an aluminum hub also gets the "heck no"
An aluminum hub CAN work, however it is unlikely that you can simply replace a steel hub with an aluminum one, because there isn't enough space engineered into the engine to do so. Not only will it need to be larger contact areas to have the same strngth, but it will also need a steel sleeve if a seal rides on it.