Lightening the OEM Crank Harmonic Balancer

Now that I have the balancer off and in my hands, it’s easy to see that this really is a big ol’ heavy bugger.

In my never-ending quest to quicken the engine’s throttle response, one small piece at a time, has anyone ever chucked this lump into a lathe, and removed maybe 10 ~ 15% of the weight by simply turning down the balancer’s O.D. by a little bit?

Is the stock engine so inherently out-of-balance that it requires such a heavy damper to “absorb” these vibrational irregularities? I would tend to think not, but there must have been a valid engineering reason why this damper was made to be so big and heavy in the first place.

I am aware of the really light weight aluminum aftermarket damper units that folks like Nick sell, and I greatly admire the craftsmanship which obviously went into their design. But for a modest street engine I am not yet convinced that I would need to take this idea that far, without also first making other significant complimentary changes beyond the current scope of work.

Surprisingly, a search of the archives did not bring up an obvious thread where this idea had been discussed before.

Thanks and Cheers - DM
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Isn't that part thick rubber or it has rubber inside? Something to that nature.

 

Yes.

or, get one of my 1.3 lb units.
Super hard anodized in Red or Gold.
PM me.

Edwardo
selling at a loss.

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I've always been a firm believer that both ends of the crank need to be matched, i.e. damper and flywheel/clutch. If the goal it acheive a faster revving engine, then design accordingly with lightened clutch, flywheel, damper and then matched with a quicker responding air/fuel mixture delivery and faster extracting exhaust. Of course, that combination comes at the price of changing the car's driving characterists - nothing is free. It all comes down to basic physics - I'm sure the engineers out there can give you a better explaination then I.

 

As near as I can figure, it has a solid outer "donut" bonded to an inner carrier with a thin piece of neoprene in between. See the joint line in my third picture above.

I'd for sure like to see a cut-away of this, though, to see if that's accurate. Judging from the weight of it, it sure seems like it's solid.

All that I'm thinking of doing is to skim maybe 1/4" to 1/2" off of the O.D. of the "donut" part.

Recalling my engineering classroom days, I believe that the polar moment of inertia of a rotating disc is a function of the radius to the fourth power, so even a little reduction in O.D. results in a big change in the moment of inertia.

Cheers - DM

 

Yup, completely agreed, I think that you might have overlooked my comment about the "significant complimentary changes" in my original post.

I certainly have no expectations that this proposed change, and this change alone, could result in oodles of free mystery horsepower. But as a piece of the overall puzzle, it seems that, as long as I have it off the car and in my hands, it might be worth a do.

Just fishing here to see if anyone else has ever been there and done that.

I certainly can't imagine that mine is an original thought!

Cheers - DM

 

It would appear we are in the same church, same pew. And let me be the first to say that I have no qualms about "modding" my QV, or any other car. My initial response to your questions was based on "why - what are you looking to achieve". Or is this just a general outreach for empirical data?

 

Dave,

Accurate but I question.

Mine has two holes cut in it whereas your has 4.

Makes me say ........ WTF??????



Edwardo,

Sorry I have been REAL busy. Planning War Games during the Silly Season is just nuts on my time.

I'll write to you tomorrow. Like Gold but I do have a question firs.

 

I did a similar swap on My subaru, canned the heavy stock pulley for an Alum 1 like above. The change was great, much smoother revs. I did nothing to flywheel or clutch. 100,000 miles later no ill effects.

 

Copied from Nick's website, speaking about his aftermarket aluminum damper:

"Each 1 lb. of mass taken off the crank/eccentric shaft is equivalent to approximately a 2.7 HP gain. "

Don't know where he came up with the 2.7 value, but one of my other cars has a lightened flywheel, and the difference was quite notable.

Cheers - DM

 

It is not a balancer but a crankshaft torsional damper and there is a reason that it is heavy.

Potential improved throttle response vs life of crankshaft. Your choice.

It's discussed in this paper available here: http://racingarticles.com/blog/2007/06/crankshaft-torsion-and-dampers.html

The only aftermarket dampers worth a damn are made by BHJ or ATI. Lightweight aluminum pulleys that replace the damper are fine if you are not concerned about engine life.

 

ditto! Article is an interesting read; ? anyone with any torsional/test data for aftermarket dampers matched with light flywheel / clutch combo's? doubtfull.

 

When I rebuilt my GT4 engine it really grieved me to bolt that heavy lump back on the end of the crank. But the engine really needs it unless you are fitting a super lightweight flywheel and racing clutch at the other end. This is one of those things that you cannot do a bit at a time. Torsional vibrations can be very damaging so the Flywheel and damper must match. I don't know how to do it, but if you are going down that route you need to find a man does. If you do the result will be great. Keep us posted on what you do.

 

I harmonic damper is very precisely designed to absorb vibrations by resonating at the frequency of the vibration but in the opposite phase. If you turn it down to remove weight the resonant frequency will change. In worst case it could actually add to the crank torsional vibrations instead of cancelling them out. This would be a crazy thing to do.

 

+100
Yes you are right here.
They match when balanced together.
( aka,, Aluminum pulley, keyways, gear ring, main shaft, New Steel flywheel with the pressure plate.)
(You must use a forged mainshaft or you are nuts.)
Then you need a matched set of rods, and 8 pistons.
(New rod nuts are required by Ferrari.)
see my spare set of rods,, for sale cheap, PM me.


Edwardo
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When it comes to rotating and reciprocating engine components, I’ve always approached this topic with a “less weight is better” philosophical mind-set. Thus the original “what if” question that I posted here.

However, after researching the information linked in this thread, as well as similar references obtained from other unrelated outside sources, I have concluded that there’s just too much unknown inherent risk for me to consider doing what I had originally proposed.

So, idea now abandoned, I will soon be reinstalling the OEM damper as is, without any modifications.

In any case, thanks to all for your input and Cheers - DM

 

+1
Harmonic balance is not a New Age belief. The damper mass is pretty carefully determined for the engine and mucking with it is risky, especially if the engine is driven a lot at high loading. I know of marine diesels breaking cranks because torsional analysis was disregarded. If you alter the damper, it should be disclosed when you sell.

 

What is the opnion about 30 year old dampers, is the rubber still good when it looks good or could it have it hardened so that the tuned frequency has changed?

 

A well-equipped machine shop or machinery test shop should have a durometer tester that will measure hardness of rubber products. It would help to know the original hardness spec. of the rubber in the damper.

 

This subject is actually a lot more complex than presented here and in the referenced PDF paper.

In particular, and in contrast to the focus of most of the torsional damper material referenced, Ferrari 8's run flat-plane cranks and are significantly over-square. The flat-plane aspect greatly changes the harmonic analysis math, and the over-square aspect means that the lever arm that the combustion and inertial forces act on is much smaller than in an under-square configuration.

Further, these are road-going engines, not drag racing nor circle-track racing motors: regardless of how much track driving we do, these engines still spend most of their life at / near idle, where torsional vibration is at a minimum, and we don't cruise at redline on the highway.

Still further, these engines have significant damping on the front of the engine in the form of the accessory and cam drive belts, and even the oil pump.

And lastly, I will point out that the factory damper has no provision for cooling, and indeed, is subject to substantial ambient heat from the partially shrouded exhaust immediately below: if the factory damper was really absorbing substantial amounts of vibration, it would self destruct in short order from inability to shed heat resulting from the absorbtion of vibration.

As a caveat I would say that I have not analyzed the damper in depth, but it seems to me that it's likely configured the way it is to tune out a small amount of residual harshness rather than as a major protective element for the crank. (My guess based on the dimunitive size would be that it attenuates a low-kHz buzz, the kind of relativey annoying buzz that would readiliy pass through the engine mounts and which would be readily felt in the flooring, and possibly seen in unwanted buzzing of guage needles.)

It would be relatively easy to check the significance of the contribution of the damper to controlling crank torsional vibration; all it requires is an engine dyno and some electronic gear. I no longer have access to an engine dyno, but I would be happy to loan out the electonic instrumentation required (a phase-angle meter)....

-f

 

Hi Frank,

Thanks for putting this relatively obscure engine component in a more balanced, (sorry) perspective.

I have long advocated reducing flywheel/clutch inertia for a more responsive, quicker accelerating engine and felt that the harmonic balancer a prime candidate for reducing mass, (definitely cheaper than Ti rods, but less effective than flywheel/clutch diets).

With people considering titanium rods, lighter pistons and taper wall wrist pins, i think this subject has some real interest and validity.

The facile hope that 1 pounds of rotational mass reduction, (regardless of distance fromthe center of roation???????) is going to = 2. something more hp is about 2 fries short of a happy meal.

But, crank longevity, is near and dear to the hearts of any of us who dump 10s of k$ into rebuilds hopeing for more hp.

Proper harmonic damping is something I consider to be near magic, that is, i havn't a clue how to go about getting the right amount, or how to change it for the better.

I hope that i haven't placed my crank at risk with my 8 pound wheel.

Dazed and confused,
chris
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But a tuned-mass damper does not dissipate energy and does not create heat. In its simplest form a linear damper of this type is a weight with two springs either side. This is the rotational version of this. The energy is stored and then fed back into the system being damped, every time it oscillates.
A viscous damper does dissipate energy but this is not this type.
But the exhaust heat could maybe cause the rubber to harden as someone mentioned earlier.

 

You're mostly correct, but elastomers as used in the stock damper are lossy and thus generate substantial heat in the process of storing and releasing energy. Thus, if really protecting the crank, this part would be sacrificial over a relatively short period of time, given the lack of cooling, the high ambient heat, and the short useful lifespan of such small elastomer bands to begin with. And, with the age of these parts today, it's most likely that their resonant f0 is very different than their design f0, if they're capable of flexing at all: it's highly unlikely that these parts are providing any crank protection today.

But the more I think about this, the more I'm confident that the Ferrari 8 doesn't need any damping on the front of the crank. In particular, by drawing a substantial amount of power from the front of the crank by way of the oil pump, the fate of the crank is left to the base design and there is little an external damper could do to change it: the quantity of force required to advance or retard the oil pump by a degree would require a phenomenal amount of energy storage / release in the damper, with attendant large shear forces in the elastomer.

Chris, the back of the crank, or the energy delivery end, is effectively 'grounded' when the engine is making power -- that is, from a vibration perspective, the back end of the crank is effectively rigidly held in position. So, it doesn't really matter what you do on that end: make it as light as you want / can. During overrun the back end of the crank is free, but the forces are greatly reduced as the motor is coasting down, so no vibration worries then. And at idle, RPMs and forces are low enough to negate any concern. So you're free to lighten the back end as much as you want, and I believe that on these motors the front end is equally unconstrained - though I wouldn't be surprised if removing the damper does lead to a small increase in NVH. Then again, that may be a benefit to some of us....

-f

 

Thanks Big F.,

Look at the 355 pulley.
No Harmonic absorption going on here.

Edwardo
I have 2 spare 208, 308, 328; 1.3# pulleys.
PM me.

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Hi.

I agree. Might want to get help from specialist engineers if you wish to proceed.

http://www.enginelabs.com/news/understanding-engine-harmonics-and-vibrations-with-fluidampr