GregBBRD

Now that I know what "NVH" is....I can answer your question.

Many people that have installed one of my dampers have reported to me that their car vibration issues are much, much better....and some have reported that vibrations they have chased for years are now gone.

How much of that is cost rationalizing?

I don't know.

I'm always trying to help the insides of these old 928 engines and anything else that occurs is just a bonus.....

.....However, logic tells me that if the crankshaft is ringing like a bell (*) and pounding on the main bearings....that "pounding" is going to be transmitted through the entire vehicle, right?

(*) Engineers claim that crankshafts, although they seem very "solid" to us are actually in a constant state of moving significant amounts. The say that a crankshaft in action is more like a molten piece of metal in how it appears in a running engine....the piston pulses move through the crankshaft like a wave would move. A damper absorbs these "waves" before they can destroy the crankshaft.

This ^^^^^is way beyond my "pay grade". I might as well go outside and try to figure out the Universe.....

hlee96

Greg, put one of these in my build if you can. Don't want to mess with a GB engine.

safulop

As I stand now with one foot already out of the 928 world, my greatest regret from the 6+ year odyssey is never meeting Greg Brown. Pretty sure my S4 could use one of those damper upgrades too! We'll leave it to the next guy.

FredR

This is a fascinating subject and something that every 928 owner should take serious note of IMHO. As he quite rightly states, folks like GB may not always know why things happen but they sure know what they are seeing/experiencing and consequently learn what works and what does not.

A couple of years ago when doing my first TB/WP job I considered changing my damper out for the spare one I have in my spare parts chest. My damper on the S4 motor is coloured orange. My spare one is green [it came from the original GTS motor]. I figured there had to be reason why they had different colours and stuck with the stock item. My motor feels very smooth but then I have no benchmark for comparison and maybe what seems smooth to me would be as rough as a "Badger's ***" to others more knowledgable.

As I subsequently learned/expected, dampers are tuned to a specific engine characteristic and given the GTS has a different crank configuration to the S4 this presumably explains the different part and why it should not [?] be mounted in the S4 motor.

Whether or not folks who rebuild these things understand these dynamics and use materials/methods that replicate the original characteristics I have no idea. Doubtless GB will have worked with the supplier of the damper to ensure an optimal tune for the damper kit he supplies.

Mileage will factor into this and high milers like Jim's GT that had some customisation/higher than stock output may well have suffered more. What would be really interesting to know is how "low milers" are faring with the passage of time wherein the rubber component is degrading/failing altogether. The vibes I am picking up from GB on his various posts in this regard is that damage due to such is becoming more and more apparent and presumably now more age related than mileage driven.

We generally tend to think of these parts as "non consumables" but clearly this is just not the case and knowing when to "bite the bullet" and hit the wallet before long term damage is done is the trick bit.

Given the damper in my S4 motor is nearly 27 years old logic tells me it does not really owe me anything. Just a question of where the priority lies relative to the other things that need TLC.

Rgds

Fred

Strosek Ultra

I like to know if Mr. Brown is using the same damper for a stock S4 engine vs. the stroker engines he is building?
Another question if we order a factory damper from Porsche how can we know it will work properly? The damper can have been stored on a shelf for quite a number of years. How fresh will the rubber be?
Åke

dr bob

As much as it might be interesting to try to "tune" the elasticity of the rubber ring to a certain harmonic frequency, it's not close to practical nor needed really. Perhaps more critical is the mass of the outer ring, but even that not so much.

Think of the crank like a bell. But lots of continuous hits from the clapper at different spots on the bell and at different frequencies. Now place your hand on the whole rim of the bell, wrapped around it. You still feel the primary excitations from the clapper, but the damping from your prevents the harmonics from continuing to excite the bell. At least most of it.

This is a complex science, not so easily explained. Bottom line though the ability of the outer mass to move relative the hub is critical. As that diminishes, the ability to absorb large low-frequency ringing goes away.

Chris Lockhart

I have always wondered about these fluid filled units:

http://www.fluidampr.com/

Strosek Ultra

Understand the ATI Super Damper part no. 917020 for Chevy SB has been used for the 928 engines. As dr. Bob say this is very complex. How do we know this is the best suited damper for a stock S4 engine or a high power 7.0L stroker?
Åke

skpyle

Hey Chris,

These Rennlist 928'rs didn't seem too impressed with the Fluidampr:

https://rennlist.com/forums/928-foru...er-damper.html


Seth K. Pyle

Chris Lockhart

Wow, definitely sounds bad! Thanks Seth.

skpyle

You're welcome!

I searched through alot of 'balancer', 'harmonic balancer', and 'damper' threads before I posted my own.

Lots of good reading there.


Seth K. Pyle

FredR

Bob,

I still struggle to understand how these dampers work. That the crankshaft has torsional rigidity issues that can and do impact timing I can understand, but I remain somewhat blank as to how these things resolve that problem. Perhaps you can concoct a magic sentence or two that explains the dynamic concept.

Given the S4 and GTS have different strokes, different specific output and presumably different torsional rigidity it is not difficult to understand why the dampers may have some different characteristics. As I can ascertain if the wrong damper is fitted/non functional it can cause catastrophic failure of the crank. Perhaps the difference between the two is the mass or the moment of inertia?

Rgds

Fred

Speedtoys

A bell has a resonant frequency, AND when a piston fires, that section of the crank out accelerates the rest of it, while a cylinder coming up on compression slows down some relative to the rest of the crank.

This sets up a wave of movement end to end in the crank..an without damping, can snap the crankshaft. The ends take the most stress at the bearings.




Put a damper on a bell, it wont ring.

Put a damper on the crankshaft..it wont ring either.

bureau13

This sounds like something to consider at my next TB job. That one's gonna be a little more costly, as I'll likely need cam gears as well.

Regarding the suitability of the SuperDamper, or whatever it's called...stock, weren't their damper differences year to year? What were those differences...color, sure, but were there other differences?

dr bob

What he said. The I interesting part is that the excitement and the ringing are "twisting" so the bell analogy isn't perfect. But close enough to appreciate the effects of dampening. For instance, hanging a damper on the end of a crank suspended vertically by the flywheel end, the damper may not do much if anything if you tap the crank. The rubber layer is designed to flex but not compress for the most part.

And, at this point I've told you more than I learned in the correspondence course from Don Bently.