Last month we opened up our email inbox to your questions for the harmonic damper experts at Fluidampr. You guys didn’t disappoint, sending in questions that actually brought praise from the Fluidampr tech team. They returned the favor, by providing detailed, in-depth replies, from a number of the team, including Brian LeBarron, Fluidampr’s marketing manager, Nick Orefice from Technical Services, and Ivan Snyder of Business Development.

Without further ado, we bring you your questions and Fluidampr’s answers.

1. Does using a harmonic balancer with a larger diameter help with controlling harmonics? – Tom U.

BL: Controlling harmonics requires inertia mass. In most cases, a larger diameter damper will carry more inertia mass and better harmonics control. The trade-off is slower revs.

For example, In Fluidampr’s line of balancers for 396 to 427-inch big-block Chevy applications, we offer 6-1/4-inch, 7-1/4-inch and 8-inch sized balancers. In drag racing applications the 8-inch is the most popular because it can handle the straight-out power the engines put out. In dirt track racing, the 6-1/4-inch and 7-1/4-inch are popular because they help provide a little faster throttle response coming out of the corners. That’s simply a popular preference. You can use a 6-1/4-inch in drag racing but the tradeoff comes in durability and performance.

2. If changes are made to the engine (rods, pistons, rings etc.,  assuming that the engine was rebalanced), then how do you “tune” a damper to meet these new requirements? – Andy B.

BL: Torsional vibration is determined by “Holzer’s Method.” In over-simplified terms, you take the mass elastic properties of each component and tabulate the natural frequency of the rotating assembly. Ideally, you design the rotating assembly so its natural frequency is outside of torsional vibration occurring throughout your RPM range. That’s not always possible, though. Especially as wide as RPM ranges have become. A “tuned” elastomer damper can be constructed to target the narrow frequency range of the worst harmonics.

There are two challenges here: 1) How do you determine mass elastics for each part in a timely way? 2) What about vibration outside that narrow critical frequency?

At Fluidampr, we use OEM-compatible torsional vibration modeling software to expedite the process. Then a Fluidampr performance damper is designed to control torsional vibration across a broad frequency range, not a “tuned” narrow band. You have the benefit of not having to “tune” the damper when engine modifications are made and it will last far longer than conventional elastomer dampers.

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3. Would one of your fluid dampeners noticeably reduce vibrations on a misbalanced rotating assembly? I know the correct approach is to pull the engine and have the rotating assembly balanced, but that is hard to justify on an engine with 90k miles that it has lived this long with the issue. – Thomas H.

BL: You will notice reduced vibration if it is originating from torsional twisting-and-rebounding of the crankshaft caused by combustion. However, if it is a rotational unbalanced vibration from mismatched reciprocating weights, then a damper itself is not the right approach. Professional engine builders will balance the rotating assembly and install a Fluidampr together to tackle vibration across the board.

4. I’m forever “arguing” with my mates that the OE damper is essentially a “balanced” compromise, and most aren’t really up to the task of most increased HP mods. That’s my view anyway! What are the merits of swapping out the OE damper for a HiPo aftermarket unit? Why should or shouldn’t you do so and is it a better way of managing the engine’s harmonics and torsional vibration even if it’s a stock mill – Rolf W.

BL: Most OE dampers are a tuned elastomer design. It contains a hub, an inertia ring, and a bonded elastomer layer between the two. The OE determines where the worst harmonics are for daily driving and tunes it accordingly. Two things happen when you modify the engine:

1) Increasing torque will overwork the stock unit and it will fail. Routinely check for cracked, bulging, or missing elastomer between the hub and inertia ring.
2) Changes to the rotating assembly — pistons, rods, flywheel, etc. — will change its natural frequency, the point where it will vibrate the worst. The stock damper is now “out-of-tune” to control it. This is why it is always recommended to upgrade to a quality, high performance broad-range harmonic damper.

Fluidampr performance dampers are designed for and used in professional motorsports. Its design shears an inertia ring through viscous silicone within a sealed housing. The benefits directly address the two concerns above. It offers superior durability compared to stock elastomer dampers and it controls harmonics across the entire RPM range.

5. Would a Fluidampr be recommended for a 6-71 blown SBC 350 on the street? The blower is driven 15-percent under, and boost is no more than 5-6 pounds. Should the damper be double-keyed? – Larry K.

NO: We would definitely recommend a Fluidampr performance damper for a built engine, especially if it is supercharged, part number 720101 for your specific application. It is a 7.250-inch OD damper that will control the harmonics of the engine better and protect your investment. We do recommend running a dual keyway in a supercharged application.

6. First, I need a physics lesson. Where is the vibration in the crankshaft? Is it longitudinal along the crankshaft, or is it in the area of thrust, the rod bearings? Is it a torsional vibration due to twisting? What wants to vibrate? What is the relationship between engine balancing and the harmonic balancer? If the engine is perfectly balanced, do you need a balancer? What is the function of a countershaft? What role does it play? – Richard B.

BL: Correct, there are three main areas of vibration: Unbalanced, Axial, and Torsional. Knowing the difference and how to address each one will contribute to overall engine durability. The harmonic balancer controls torsional vibration. Torsional vibration is the end-to-end twisting and rebounding of the crankshaft caused by combustion.

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These diagrams show the different types of vibration. Rotational (left) is from an unbalanced rotating assembly. Axial (center) comes from excessive thrust clearance. Torsional (right) comes from the application of power and is what is controlled with a harmonic damper.

The confusion comes with the term “balancer” and assuming an unbalanced vibration. A harmonic balancer only contributes to rotational balance if it contains a counterweight. This configuration is an externally balanced engine and they are common among classic muscle cars. For example, Chevy 454ci to 502ci big-blocks and small-block Fords. With external balance engines, not all the crankshaft counterweights fit inside the block, so it’s added to the harmonic balancer and/or flywheel/flexplate. Finally, A balance shaft, found in-line fours, will counteract its inherent rotational imbalance.

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On the left is an internal or neutral-balance damper. On the right is one with a built-in counterweight for an externally balanced application.

7. How does the size and/or weight of the inertia ring of the balancer correlate to the engine rotating mass? How do you arrive at the viscosity of the fluid vs. the clearance inside the damper? – Ted A.

IS: The size of the inertia ring is much more related to the space available for the damper. Once the space is determined, we size the ring appropriately from that point forward. Then we determine material density based on the amount of inertia required. Once we have the base inertia to start, we create a multi-mass model and use the resonance rates between the ring and the engine inertia to determine the required spring rate. That is when we determine clearance and fluid viscosity, in order to set the required spring rate between the ring and housing.

8. My question is about using the Fluidampr on an antique tractor engine. We use these engines in tractor pulls. They came from the factory to be used at 1,000-1,500 rpm. For pulling we turn them up to 2,500-3,000 rpm. Is there a need or benefit to using the Fluidampr? Also, these engines may be 400ci up to 1,500ci, with or without power adders. Thoughts? – Don H.

NO: A harmonic damper is always a good idea and a benefit in every application. Fluidampr offers specific tractor-pulling dampers. Part numbers 1243101 and 1243111. These are SFI-certified and made from solid billet material, black zinc coated with laser engraved timing marks. The main benefit to using a viscous damper is it protects in real-time to combat the engine’s harmonics throughout the entire RPM range, no matter what modifications or power adders have been used.

9. I have a muscle car with a small-block Chevy; stock bottom end rotating assembly, moderate cam, heads, and intake. I can easily make power to 6,500 rpm, but with a stock bottom end, I’m afraid to spin it above 5,200 rpm, so I have my EFI rev limiter set to 5,500, which I usually hit once every other week when I take it out to play. My question is, can your dampener safely extend my RPM range above 5,200, and can your dampener extend my engine’s life? – Robert V.

IS: There are so many factors that go into an engine build that make each application unique. For example in this case, you have performed some modifications to the top-end but have a stock bottom end. To 100-percent claim a Fluidampr will safely allow you to increase RPM would be irresponsible speculation due to all other unknown factors.

What we can 100-percent claim is that a Fluidampr, due to its unique viscous design, is able to control a broad range of harmonic frequencies across the entire RPM, whereas with an OEM elastomeric (rubber) damper you are limited to a narrow frequency spectrum as designed by the OE engine mfg. when the SBC engine was developed for daily use driving. This broad range protection will ensure less wear on critical engine components over time and, other factors aside, will increase longevity.