Engine/Transmission (1994 - 1998) Harmonic Damper

[Willie G]

Has anyone used a Fluidampr harmonic damper on a 12 valve? If so, how good is it?

 

[DHorstman]

Was just down at a machine shop getting some work done on a SBC. Found something interesting, the company that makes SCAT cranks has a brochure that has 5 main reasons for broken cranks. #3 was fluid dampeners or any other self balancing dampener. Called another shop and they said basically the same???

 

[PKemp]

Thats peculiar considering they are practically a standard item on race vehicles, continuous run power generators and all 45 of our heavy class 8 diesels (Mack, International, Cummins, Volvo). Plug "Fluidamper" into the search screen and see what you get.

Look here: http://www.vibratechtvd.com/thesource.htm

 

[HEMI®Dart]

This is what SCAT crankshafts say about dampers:



A word about vibration dampers

In our conversation, Tom Lieb gave us some great (though sure to be controversial) information about a subject directly related to the crankshaft and its survival in a race engine: vibration dampers. He was quick to point out that a very common cause of crankshaft failure is using the wrong damper, and is especially leery of any damper that has moving parts. "A damper is supposed to balance an engine. How can you do that when you have something moving on the damper?" Lieb went on to say "Any damper with moving parts, whether it is fluid or mechanical, is not recommended in a drag race engine. Anything that moves in the damper has inertia. When you quickly accelerate or decelerate the engine, that moving part of the damper slams one way or another and puts a lot of stress on the crankshaft. For an engine that runs in a very narrow rpm band and with very little change in engine speed, like an 18-wheeler or a car that drives on the highway at a constant speed, a damper with moving parts is fine, because it will find the frequency at a constant rpm and dampen the vibrations. But with a drag race engine that accelerates and decelerates fiercely, the engine will only have certain vibrations for a millisecond. " For a drag racing engine, Lieb recommends the lightest, smallest damper possible, with an elastomer-type construction. "The rubber will sit there and hum, but it won't change location. "



It looks like for our application, a fluidampr would be beneficial.

 

[DHorstman]

It looks like for our application, a fluidampr would be beneficial.

sounds good. Makes sense as the two shops I talked too do a lot of race engines.

 

[Vaughn MacKenzie]

"A damper is supposed to balance an engine. How can you do that when you have something moving on the damper?"

This doesn't apply to internally balanced engines such as the Cummins B series.

When you quickly accelerate or decelerate the engine, that moving part of the damper slams one way or another and puts a lot of stress on the crankshaft.

Does a damper really have parts slamming back and forth?

But with a drag race engine that accelerates and decelerates fiercely, the engine will only have certain vibrations for a millisecond

Also doesn't apply to a Cummins and most other engines since they don't accelerate wildly like a radical drag motor.



Hot rodders often use aftermarket harmonic balancers. Those building Chevy straight 6s with its skinny long crank a Fluidampr or similar damper is a must. Stock dampers are designed to take care of the worst harmonics but can't damp them all. Besides first-order harmonics I believe the Fluidampr covers 2nd & 3rd order or more.



I read on another forum an engine crank can twist more than 3 degrees from end to end, and good aftermarket dampers can cut that in half. The greatest harm comes when the crank snaps back, hammering the rod bearings at the front end cylinders. I'll have to see if I can dig the discussion on torsional crank flex.



Vaughn

 

[Vaughn MacKenzie]

Here's some info.



http://www.indiacar.com/index2.asp?pagename=http://www.indiacar.com/infobank/torsional_vibration.htm



This graph is on that link above



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[WDixon27]

i saw a thing on top fuelers about how the crank twists so much they build the cam with a twist so the front and back cylinders are not too far out of sync

I read on another forum an engine crank can twist more than 3 degrees from end to end,

 

[HEMI®Dart]

Good posts Vaughn. Thanks for clearing up some issues.



Maybe after the holidays I'll get one. It's not a cheap bomb by any means. Summit Racing will have them end of Dec.



Anybody know how much the OEM 12V Cummins Damper weighs? The new Fluidampr weighs 24 lbs.



http://store.summitracing.com/defau...rch&DDS=1&N=115&target=egnsearch.asp&x=28&y=6



"Fluidampr controls the

harmful torsional vibrations in the crank shaft much better than the

stock rubber damper. A stock rubber damper is a tuned absorber and

works only on one order of torsional vibration while the Fluidampr will

control all three orders of vibration in the operating range. As a

results, your crank and bearings will last longer and the engine will

produce more horse power and torque. You possibly may get slightly

better fuel mileage. "

 

[Vaughn MacKenzie]

I doubt the OEM weighs 24lbs, just a wild guess maybe 16-18lbs.