Brian LeBarron is an associate at Fluidampr. He is a 17 year veteran of the motorsports and powersports industries with several published articles and co-presentations on the advantages of viscous damper technology. Brian is also a member of SEMA’s Young Executives Network. Over the past six months he went behind-the-scenes with Fluidampr’s engineering team and documented the challenges and accomplishments that went into developing a new performance crankshaft damper upgrade for the Subaru FA20 / Toyota 4U-GSE ‘boxer’ engine. – Editor

Fluidampr performance dampers originated during the mid-1980s when parent company, Vibratech TVD, was approached by high level race engine builders. Their goal was to bring the durability and broad frequency range protection of a viscous damper found in commercial and industrial applications to professional motorsports. Today, Fluidampr performance dampers continues to be one of the market-leading premium crankshaft dampers sold for domestic, import, and diesel street performance and motorsports applications.

Fluidampr performance dampers challenge the misconception that a viscous damper is only suitable for large, low rpm industrial and commercial diesel engines. In this article you’ll be able to follow the design and development process, plus comparative testing, of a new Fluidampr performance damper for the Subaru FA20/Toyota 4U-GSE 2.0L opposed-four cylinder ‘boxer’ engine. The engine is featured in the popular 2013-present Subaru BR-Z, Scion FR-S, Toyota GT86 and new 2015 Subaru WRX.

Design Criteria

In conjunction with Turn 14 Distribution, the process began by implementing Vibratech TVD’s ISO 9001:2008 design and development certified process. This is the same high quality company standard used in the development of viscous dampers for OEM powertrain partners in the aviation and defense industries. Objectives were first established by interviewing intended users, understanding the challenges they face, and analyzing the technical specifications of the engine.

Above all, the new Fluidampr would have to prove that proper crankshaft torsional vibration damping is necessary in a boxer engine and that a viscous style Fluidampr crank damper can outperform the stock tuned elastomer style damper. As a bonus, given the popular misconception that no damping is needed on a boxer engine, it would also need to be compared to a leading lightweight crank pulley alternative.

From those market and product research sessions, the following goals were established:

• The damper would need to be light weight, yet effective and durable. It would be required to pass the strict professional racing industry’s SFI 18.1 safety certification. According to SFI quality assurance specifications, section 18.1 refers to crankshaft hub harmonic dampers.  Article 3.0 Construction dictates that, “the damper shall be constructed in such a manner that the inertia devices shall not become disengaged during use. For inertia disc style dampers, the containment device must cover a minimum of 50 percent of the cavity containing the disc.  The thickness of the containment material must be a minimum of 0.062-inch steel or 0.180-inch aluminum.”  Article 5.1.3 B Testing Procedure mandates that, “The damper shall be driven to a rotational speed between 12,500 and 13,500 rpm and maintained at that level for one hour.”  Furthermore, the steel of a SFI certified Fluidampr housing must meet a minimum 40,000 psi yield strength and 60,000 psi tensile strength under testing.
• The damper would need to provide broad frequency and amplitude coverage to account for a wide variety of engine modifications, including changes to the bore and stroke, rod and piston composition, crankshaft composition, and the potential for much higher cylinder mean effective pressure.
  • For quality conscious race teams, in addition to providing excellent torsional vibration protection, the damper would require superior longevity and no maintenance, tuning or replacement once installed.
• Through creating greater efficiency by controlling torsional vibration, the damper would need to release more lost torque and horsepower over the stock tuned elastomer damper and a lightweight pulley.
• The damper dimensions would need to remain as close to stock as possible.
• The damper would need to accommodate additional accessory drives, such as a dry sump system or supercharger.

“Viscous damper technology will provide the broad frequency range and amplitude control. The toughest challenge is going to be fitting enough inertia mass in the same amount of physical space the stock damper consumes,” remarks Aaron Neyman, Fluidampr Senior Product Engineer.

Tuned elastomer-style dampers bond the inertia mass to the outside diameter. Its leveraging effect provides a functional design in a smaller and lighter package. A viscous-style damper carries a portion of its inertia mass in the outer housing with the remaining mass contained in the inner inertia ring. The advantage of the viscous-style design is that the outer housing provides heat dissipation that contributes to overall superior damper life.

Measurements

Through membership in the Specialty Equipment Manufacturers Association (SEMA) Technology Transfer Program, details regarding the FA20 / 4U-GSE engine were obtained. In addition, an OEM crankshaft damper and timing cover were obtained. Through the use of calibrated precision measurement equipment, the dimensions of the OEM crankshaft damper and timing cover were configured. In combination with other data obtained, measurements confirmed that the Fluidampr performance damper would be restricted to the same 5 7/8-inch outer diameter dimensions as the OEM crankshaft damper.

Layout then began in computer-aided design software from the measurements collected. Detailed finite element analysis was performed to determine the damper’s resonance frequency and structural integrity.

SFI requirements mandate the damper to be spun at 12,500 rpm for one hour without failure to meet certification for professional motorsports. The materials and manufacturing process chosen for this Fluidampr application provide nearly four times the requirement for added safety.

Once the preliminary computer design was complete a 3D additive printed prototype was produced.

The prototype was shared with established performance engine shops to verify fitment and tolerances using actual engines. With the ABS plastic prototypes passing inspection and the design meeting the initial objectives for optimum weight, size constraint, and provisions for future accessory drive changes, the team moved forward with creating fully functional test prototypes.

Validation Testing

“Computer modeling and rapid prototyping is fantastic,” comments Neyman. “The true test however is how well it functions. In motorsports it has to outperform and outlast the stock crankshaft damper.” To validate the new Fluidampr performance damper, the team partnered with the well-recognized speed shop, R/T Tuning in Montgomeryville, Pennsylvania.

“We want to get as close to a common real world setup as possible,” continued Neyman. “We know high power builds benefit extraordinarily well from a Fluidampr performance damper because you’re inducing much greater torsional vibration amplitudes and heat than what the stock tuned elastomer damper is designed for. For this validation test we went the other direction.”

Steady state data was taken at idle to determine if the laser sensor was adjusted properly in order to provide clean data. This setup was also used on the Fluidampr performance damper to eliminate a possible variance due to dissimilar fixtures. For torsional vibration measurements, data sets were taken using speed sweeps from 2500–7500 rpm over a time of 30 seconds in order to capture any resonance points in the operating range of the engine. Each speed sweep was conducted twice, back-to-back to verify consistency.

The laser sensor generates digital signals that are counted thousands of times per second and then run through a fast Fourier transform (FFT) to calculate speed fluctuations of the crankshaft hub, across the engine frequency spectrum. The result plots the amplitude of each vibration order across the rpm range and determines system resonance frequencies. Figures 1, 2 and 3 below show the overall torsional vibration map for each test.

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(Fig. 1) FA20 engine torsional vibration map with the OEM tuned elastomer crankshaft damper. The first crankshaft resonance appeared at 88Hz and was almost below the testing rpm range. A second crankshaft resonance was also seen near 260 Hz. (Fig. 2) FA20 engine torsional vibration map with Fluidampr performance damper. The Fluidampr performance damper effectively reduced all vibration amplitudes to less than 0.25 degrees peak across the testing range. Amplitudes also show a general reduction trend while approaching the upper limit of the rpm range. (Fig. 3) FA20 engine torsional vibration map with an un-damped lightweight pulley. The lightweight pulley shifted a third crankshaft resonance into the operating range at 600Hz. The 600Hz resonance excited 5.5th and sixth order vibrations. High frequency amplitudes carry much more stress than equivalent low frequency amplitudes because they occur more times per revolution. In this case, even though the amplitudes were similar, without the proper crank pulley weight to keep the resonance point out of the rpm range, the frequency stress level felt by critical internal engine components rose three times. Crankshaft driven timing components and oil pump drives can be more susceptible to these high frequency vibrations.

After reviewing the vibration overview waterfall plots some individual orders were examined to show the differences in detail. An order is how many times a vibration event occurs during one revolution.

To the right are the comparative torque and horsepower results.

High rpm gains align with areas where the Fluidampr performance damper outperformed in terms of torsional vibration control.

Superior damping freed up horsepower and torque through overall engine efficiency gains previously lost due to torsional vibration.

Conclusion – Lighter Is Not Always Better

Comparative gains between 4,000 rpm–7,000 rpm at only 150 rwhp peak on a boxer engine is impressive. One can only conclude how much of an improvement the Fluidampr performance damper would make at much higher horsepower. Why did the Fluidampr, at 4.6 pounds heavier than the 1.195-pound lightweight crank pulley, come out on top?

“Excessive crankshaft torsional vibration robs power and accelerates component wear. You need proper mass with broad range damping to control it. The more power you add, the more you need to upgrade to a quality viscous damper for durability and optimum performance,” concludes Neyman.

“Mass also determines where rotating assembly resonance points will occur. As shown during testing, without proper mass the lightweight pulley shifted a new high frequency resonance point into the operating range. Flywheel/flexplate, crankshaft, and rod & piston changes can all have similar harmonic effects.”

The second advantage in favor of the Fluidampr performance damper is the concept of rotating weight. While the overall weight is 5.8 pounds, because the inner inertia ring is not bonded and freely rotates, its weight is not fully felt by the crankshaft once the engine is operating. It can be calculated that the rotating weight of a viscous damper is roughly 2/3 its overall weight. This means at rpm, the rotational weight spinning in unison with the crankshaft feels more like 3.8 pounds. That, plus broad range damping, gave it the edge over the stock tuned elastomer damper.