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Fluid Situation - Does Your Car Need a Viscous Damper?

Fluid Situation - Does Your Car Need a Viscous Damper?
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There are two reasons to consider using a viscous damper in your hot rod.  If you have made any performance modifications to the engine, a fluid damper is a good idea. A performance type fluid damper is a must if your hot rod is going to be running in competitive events that require an SFI 18.1 spec harmonic balancer. A fluid damper is also a good idea for any car - not just a hot rod - with a stock elastomer harmonic balancer that has cracked, missing or bulging rubber.

As an automobile engine spins, it creates torsional vibration, a slight twisting and rebounding of crankshaft motion caused by the initial torque load of each power stroke. A viscous damper has a fluid inside of it. As the damper rotates the gyroscopic force of the fluid helps to control a broad range of torsional vibration frequencies. A silicone fluid is the best dampening media we have.

In an April 2012 article, Bob McDonald of Engine Builder said that engine heat can cause a conventional harmonic balancer to deteriorate and develop torsional twist that can ruin a crankshaft. “I believe the best way to dampen harmonics is with a damper that incorporates a silicone gel,” McDonald wrote.

Some hot rodders point to lightweight crank pulleys as an option, but actually a sufficient mass is required to control torsional vibration. A lightweight pulley, by itself, offers little or no protection against torsional vibration. On the other hand, viscous dampers are designed for smoother engine operation.

A typical model such as the Fluidampr Performance damper starts out as a precision machined and carefully balanced housing. A shear gap is part of the design. Torsional vibration suspends an internal inertia ring within the shear gap. When it’s suspended and free floating, a crankshaft doesn’t have to rotate both damper components at the same rpm. This reduces what is called parasitic drag and achieves a lower rotating weight.

A damper like the Fluidampr Performance model has a steel flywheel inside the housing. It serves as an inertia ring. This helps reduce wear on critical engine components, fight crankshaft failure, improve valve timing and increase horsepower and torque. Because this damper supplies proper mass, it lasts a long time and no rebuilds are required. Viscous dampers are available for many popular hot rod engines. In fact, Fluidampr even offers a model for the iconic flathead Ford V-8 which went out of production in 1953.

Graph shows how vibrational forces increase with speed.
Graph shows how vibrational forces increase with speed

Red line shows that horsepower at speed increases when a viscous damper is used
Red line shows that horsepower at speed increases when a viscous damper is used

The viscous damper is designed for smoother operation
The viscous damper is designed for smoother operation

Rubber dampers are tuned for a specific frequency range.  Engine mods alter that frequency range
Rubber dampers are tuned for a specific frequency range.  Engine mods alter that frequency range

Cracked rubber on a stock damper showing early signs of wear

Here’s a stock rubber damper showing advanced signs of wear