Simple.

Factory-style elastomeric dampers are tuned to dampen harmonics at a specific frequency (rpm) which is determined from an exact engine combination of recip weight and crank stiffness. It is also flavored with the engine speeds found in auto usage.

Any change in rotating mass or intended operating range or crank stiffness will change the harmonic behavior of a motor.

A Fluidampr uses a thick silicone based oil to dampen and it is effective over a wide range of rpm. Not just tuned to a single target frequency.

Then the safety aspect: A good backfire can sling the outer ring out of position on a stock damper. The outer ring can come off (never seen it hapen on a boat, but it CAN).

Formula31,
Here is a tech paper that should help explain. Some advantages of controlling the torsional resonant frequency include extended bearing life and more stable valve train. Crankshaft excitations can be transmitted to the valve train via the cam, often resulting in spring surge.
Hope this helps,
Bob
http://www.epi-eng.com/ET-TorsAbsrbrs.htm

Ah, thats what I needed to know. Thanks mcollinstn, rmbuilder. It make more sense now.

I dont need to have the rotating assembly rebalanced again if I switch, do I?

Fluidampr
It depends on whether the engine is internally or externally balanced.

Internally balanced engines - No. Fluidampr is completely neutrally balanced and no additional balancing is recommended. All of Fluidampr's components are individually balanced at the factory. We recommend that you balance your engine with either the stock damper or with no damper.

Externally balanced engines - It is recommended that the Fluidampr's counterweight be match balanced to the existing stock damper or balanced with the assembly. However, in the case of Chevrolets and most Fords, if the original damper counterweight has never been altered, then the Fluidampr is a direct replacement for the stock damper. When the Fluidampr is balanced with the assembly, it is necessary to separate the ring from the counterweight and balance the Fluidampr with the counterweight portion only. After balancing is complete, reattach the ring.

ATI
Internal balance units have each part of the damper accurately balanced to 1/10 oz./in. before assembly. These units should not be on the crank for balancing as the inertia weight may not be centered until the engine starts.

External balance GM 400 and 454 are identically balanced to GM service balance specifications. The hub and weight only should be installed for crank balance.

Since all hub/weights are identically balanced, ATI offers a slip fit hub and weight assembly for both the 400 and 454 allowing you to balance before pressing the damper on the crank. Replacing a damper on a previously balanced engine in all applications requires match balancing the Super Damper™ to the existing damper unless the previous damper was an unaltered ATI unit. ATI can match balance a Super Damper™ to your existing unit accurately and promptly.

I read all that info and still not sure. It is an externally balanced Mark 4, rotating assembly balanced with the stock damper (which appears to be intact and not altered). Will off the shelf be correct or does the damper have to be sent in to be matched?

Off the shelf X-bal BBC Fluidampr is balanced identically to an off the shelf X-bal GM damper.

Direct swap. NOW, if the rotating assembly is nonstock (different or larger pistons - different rods, chenged to floating pins, etc..) then you should balance WITH the damper hub on the assembly.

Formula31,

I have a Fluidamper for a Mark IV with only two hours on it if you are interested. PM or call 419-882-1680.

Direct swap. NOW, if the rotating assembly is nonstock (different or larger pistons - different rods, chenged to floating pins, etc..) then you should balance WITH the damper hub on the assembly. [/B][/QUOTE]

Ok, the rotating assembly is non-stock, however, it was balanced with the stock balancer and flywheel. So, the stock weight aftermarker balancer is OK then-right. I'd rather not have to pull this whole shortblock back apart again. Id just use the stock balancer first.

USE ONLY ATI OR ROMAC, STAY AWAY FROM FLUID
DAMPERS THEY NEVER BALANCE CORRECTLY.

I have ATI on all my motors.

What happens when the fluid in that dampener changes temps ,changes density??

Some of the supercharged engine builders don't use a dampener


5000rpm or lower for your application its if you just want to spend money.