July '16

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10 PRECISION ENGINE JULY 2016 Design engineers know exactly where to address the issue to achieve optimum efficiency and durability. Validation testing then further proves out analysis and mod- eling. Help your customers think like a pro. Everything may look great on paper or online until you fire the engine. Once you do that, vibration and heat are introduced. You need to compensate for it. Analysis and comparative dyno pulls have proven a properly designed damper, although often weighing more, can actu- ally improve performance by reducing and controlling torsional vibration. WHERE THE HARMONIC BALANCER FITS IN To control torsional vibration, you need to reduce the twisting and rebounding of the crankshaft being caused by combustion. To accomplish this, you need to leverage an optimum amount of mass at the right time and remove that vibration energy from the system. This is why weight, diameter and fre- quency coverage are important consider- ations when selecting the right harmonic balancer. Stock harmonic balancers operate by bonding an elastomer material between a hub and an outer ring. The durometer of the elastomer and mass of the outer ring determine where it can control a narrow frequency range of the worse vibration. Where this occurs, there is a lag between the movement of the hub and ring. Vibra- tion is reduced by the inertia mass of the inertia ring deforming the elastomer and generating heat. This approach is often referred to as an elastomer damper or tuned damper. These are adequate for everyday stock vehicles where torsional vibration properties are consistently known. A viscous damper works by enclosing the inertia ring in a housing with a small amount of specialized silicone. Vibration causes the inertia ring to shear through the silicone in-and-out of phase with rpm. Shearing transforms vibration to heat, which radiates through the outer housing. Silicone is used because it maintains vis- cosity tolerance across a wide temperature range, commonly minus-40 to 300 degrees. This design is superior in product life and allows vibration to be controlled over a broad frequency range. You will often find viscous dampers as original equipment on high-end luxury performance cars. They are also ideal for when engine modifications are made and you are not certain where the worse tor- sional vibrations now occur. While more premium and luxury OEMs are embracing viscous dampers, they are not always race-ready. First, they lack SFI 18.1 design and safety certification. Second, a higher consideration for heat dissipation may not be designed in. Third, high-quality materials and strict manufac- turing processes are needed to ensure race durability. The investment in premium quality and an established brand is well worth the cost when choosing a viscous damper for racing applications. A simple check for cracked, missing or bulging rubber between the hub and inertia ring is a telltale sign to upgrade to a viscous damper. (Photo courtesy Fluidampr) PRECISION ENGINE VIBRATION ISSUES

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