Why Torsional Dampers Are Crucial To The Health Of Your Engine
There’s no denying the fact that piston engines shake, some more than others. The vibration that is created by an engine has to be controlled somehow, and this is the reason why torsional dampers exist. We all understand that fact, but what are dampers? Is their power to be found by having the correct one for your application?
These are the questions that we wanted to get answered also. So we went to the torsional damper experts to find the answers to our questions. Our friends at Fluidampr, TCI Auto, and ATI Performance Products fielded all of our questions and you might be quite surprised to find out how this often ignored piece of equipment is vital to the health of your engine.
How Shake Happens
Consider that a piston stops traveling altogether twice per revolution (at the top and bottom of the cylinder) and you can imagine how much energy that represents. Then the shock from the connecting rod, and transfer those forces to the crankshaft. Finally, add the difference in torque that is applied to the crank, and all of this is working to twist that crankshaft, loading and unloading it like a spring.
On your gramma’s grocery-getter, the damper’s weight doesn’t matter; but on high-performance engines, every bit of weight counts.
While we recognize the damage such vibrations do directly to crankshafts, these vibes can also degrade components like distributors or accessories like your alternator, oil pump, etc. Not to mention if the crankshaft flexes too much, it can throw off your cam timing and rob you of power.
Crankshaft vibration is inherent in any internal combustion engine because of the powerful yet uneven forces that act directly on the crankshaft. Understand, a damper will not add horsepower, but crankshaft vibration will handicap the engine’s horsepower potential.
“Design engineering can calculate the harmonics; but testing also shows where the frequencies are,” said Brian LeBarron at Fluidampr. “When you make performance upgrades, you can change where the critical harmonics occur.” The ‘bad’ harmonics build up in a complicated but predictable way, that’s why dampers are tuned for specific uses, as well as for specific engines.
“While your motor is running, you have some pistons that are being pushed downward on a power stroke, some that are being pulled down by the crankshaft, and then there are some that are being pushed upward by the crankshaft,” explained ATI’s J.C. Beattie Jr. “Now think about this entire system happening 8,000+ times per minute!”
The vibration damper reduces these harmonics (particularly the larger, more-destructive “lower order” vibrations) and keeps them from building on each other. Engineers figure out where the harmonics come into play.
On your gramma’s grocery-getter, the damper’s weight doesn’t matter; but on high-performance engines, every bit of weight counts, and rotating weight particularly, since it accelerates with engine speed, and also because it produces a gyroscopic effect. Engine modifications can move the harmonics outside the tuned range of the OEM damper, making it useless.
How Do They Work?
Several approaches to damper design are popular, some are complicated and some are simple. Three popular designs dominate:
- “Rubber” Elastomeric (Lanchester) damper
- “Pendulum” damper
- “Fluid” (Houdaille) damper
Elastomeric dampers work well against the predetermined, big, crank-destroyer first-order harmonics. The pendulum type’s manufacturer says it can confuse nearly all the harmonics, small to large. Viscous dampers are effective across a broad frequency range to protect against the crank-destroying and secondary harmonic effect.
Elastomeric dampers typically use two rings of metal, separated by an engineered polymer. One ring attaches to the crankshaft, the other ring is heavy and is matched to a particular engine’s known vibration frequency at a specific rpm, where that inherent harmonic can do the most damage. The two rings are separated from each other by elastomers, typically scientifically-designed polymeric “O” rings.
OEM dampers are usually of the simplest and cheapest elastomeric type. Rubber is poured or forced between concentric steel two rings in a liquid state; then it dries in place. There are usually serrations on the OD of the inner ring and the ID of the outer to help hold this rubber strip in place.
For example an ATI Super Damper uses two concentric rings – an inner one to connect to the crankshaft directly, and an outer one, with weight and diameter designed to counteract the torsional vibrations of the crank. Between these are two O-rings of such size, shape and material to allow the optimum tuning for your particular application.
Over time in your street car, that rubber can deteriorate through exposure to oil, temperature, and mechanical fatigue. Performance elastomeric dampers on the other hand, are much more robust, not to mention rebuildable like ATI’s Sumper Damper. ATI’s J.C. Beattie Jr. notes, “You say OEM dampers are ‘cheap!’ I have been told an OEM damper for a very popular V8 has a cost to them of under $10… And guys will put that on their $30,000 engine!”
“Your stock damper, or stock style damper, is simply a piece of soft steel that has a rubber ring that has been melted in between another steel ring,” Beattie explained. “The inherent problem with that design is that there is no way to maintain concentricity of the inertia ring during manufacturing.” Beattie went on to claim, “Through many years of testing and tuning, the O-ring style Elastomer damper has proven to be the best choice for performance applications, especially when high RPM is being applied.”
The viscous damper was invented in 1946 by Vibratech TVD (formally Houdaille and parent to Fluidampr). Vibration resonates an internal inertia ring causing it to shear back and forth through a thin layer of highly viscous silicone fluid. The shearing action transforms the energy into heat, which safely radiates through the outer housing. Specialized silicone fluid (on average 45,000x more viscous than 30w oil) is used, as it has proven to have good thermal stability, plus it has high tensile strength and heat dissipation properties. The fluid style is considered by its maker as effective on a wider range of rpm.
Because the fluid is not significantly degraded if used within its operating ranges for temperature, vibration, and rpm, maintenance is ordinarily required only if the unit is physically damaged. These are also popular in long-life, high-shock applications, like diesel trucks, and off-highway equipment.
Fluidampr’s LeBarron notes, “Each of our damper applications are engineered and tested to the actual vehicle, rpm range and conditions it’s expected to encounter. Well, for example, our new CT Gold series dampers have been developed for today’s higher rpm circle track cars. The centering technology feature allows a CT Gold series damper to be balanced with the rotating assembly, plus provide enhanced torsional vibration control for sustained RPMs above 6000.”
Fluidampr claims their silicone fluid will not freeze or thin out with ambient or engine temperature changes, or go bad with age or from sitting idle. Unless physically damaged (or if the press fit has been lost from repeated removal), Fluidampr says their damper will last the life of the engine in performance applications.
The “pendulum” damper like the TCI’s Rattler’s design evolved from oil-filled aviation designs, and consists of tuned weights whose masses, indirectly connected to the crankshaft, take up the “snap” produced by the torsional vibrations. Being tuned to frequencies outside the engine’s own, they work on multiple frequencies, and may continue to work well, even after, say, a piston-style change.
Scott Miller at TCI says, “The weights inside the Rattler are different diameters, and they are balanced, depending on the engine type and firing order. These pucks actually roll [in a dry environment] within their cylinders, and are ready at the crank’s end just when the vibration is trying to ‘exit’ the crankshaft. This action effectively absorbs the action of the crank.” The Rattler is inaudible except at shutdown, as the engine drops below about 500 rpm, when the pucks can get free from the normal centrifugal force.
“The damper in a stock application – the OEM setup – is ideal for that engine,” said Miller. “But any time you make changes in the engine – and not just the crank and rods and pistons, but even a carburetor – these changes can make your OEM damper ineffective. Do other dampers work? Yes; but wouldn’t you rather eliminate the vibrations, rather than dampen them? The Rattler extends the frequency range and eliminates the vibrations, rather than just toning them down.”
The Rattler lives with a reputation as a noisy thing. The noise is evident at shutdown, but only as the engine drops below about 500RPM and centripetal force no longer keeps the internal pucks plastered to the outsides of their bores. “The myth of ‘greater maintenance’ is something I’d like to see go away. Plus, your whole engine will last longer – less engine maintenance on those expensive parts is where you save money,” said Miller.
What Do They Do?
When your crankshaft’s twisting moments build up, the crank fights back, and when the loads are high enough, the crank’s return to “normal” is a violent reaction, sometimes nasty enough to break that big expensive piece of metal. A torsional vibration damper can lessen the sharpness of the buildup, and also relieve the tension a bit slower; these two actions greatly lower the loads on the crank itself. The extra energy is then transmitted through the damper, resulting in a measurable buildup of heat. The materials of the damper (either elastomer or fluid) are designed to be effective through the predicted range. (The TCI Rattler has no rubber and contains no liquids, and so doesn’t generate heat.)
One advantage of all high-performance dampers is that timing marks are prominent on their circumference, giving you a built-in degree wheel for setup and tuning. Although not as precise as a large-diameter degree wheel that would never fit under the hood, they provide a reliable, available reference for all sorts of field work and routine tuning.
Dampers don’t add horsepower, like Miller explains, “We don’t push the Rattler as a horsepower enhancer, what it does is extend the life of the engine.” Dampers allow the engine to live longer, of course, that means that you can now do other things that would shorten its life (like adding horsepower).
One manufacturer claims a “45 hp increase” on one race engine that switched to its damper, and cites a well-documented example. They explained to us, “Basically going from the wrong damper, to the best one, you can get huge amounts of power.” True – just as you can gain power by going from the wrong camshaft to the best one. The right damper is always better than a mismatched one.
Keep in mind the tradeoffs between damping ability and weight: more weight (other things equal) means better damping. But other things aren’t equal – larger diameters can sometimes increase the damping effect without adding weight, because the weight is working on a longer lever arm.
|Type||Main Advantages||Main Disadvantages||Examples|
|Viscous Fluid||works across slightly broader range of frequencies than elastomeric; works in particularly tough (e.g., diesel) applications||relatively expensive; reduces vibrations in tuned frequency band only||Fluidampr,
Fluidampr CT Gold
|Elastomeric:||cheap (OEM) to expensive; effective within its predetermined limits; good in high-rpm applications; often rebuildable||reduces vibrations in specific, tuned frequency only; could be damaged||ATI Super Damper|
|Pendulum||effective over full range of rpm; does not generate heat||relatively expensive; noisy in low RPMs, less common in race applications||TCI Rattler|
|no damper||free; weightless; takes no space||permits all torsional vibrations|
Your original engine probably incorporated a damper, typically integrated with the pulley on the end of the crankshaft. (The flywheel and clutch or torque converter typically deal with harmonics at the other end.) Replacing that damper pulley with a “power pulley” (generally promising to lower overall weight and the rpm of accessories and water pump, reducing “power drain” from accessories and eliminating the possibility of the water pump’s cavitation at high rpm) will do nothing to attenuate torsional vibration, and may reduce your crankshaft’s life by a factor of [some literature claims] ten.
It’s good to plan ahead, but order your damper only after your engine’s design and makeup are pretty well set. Know what the clearance around your damper mount will be; then determine which model of your favorite torsional vibration damper will work best. For all applications that are outside “essentially stock,” you’ll need to know more than your engine size and model: your working rpm range, compression, aspiration (turbo, supercharged?); did you change internal components (pistons, rods, crankshaft, camshaft or cam drive, lifter type, flywheel, clutch or torque converter) or major drivetrain components (driveshaft / length, transmission or differential )?
To Spend, Or Not To Spend?
Fluidampr’s LeBarron explained to us, “When you talk about a $20,000 engine, is the extra $400 for a good damper to protect it really expensive? You’ll also free up lost hp and torque (a very small amount, but measurable).”
We all hate to add weight, and a torsional damper looks like another chunk of stuff we’d be better off without. That depends, of course, on how long you want your engine to last. For most folks, longer life is worth it.
One of the manufacturers explained to us, “As you know, there’s plenty of unsupported claims, mis-information, skewed testing, mudslinging rivalries and those sorts amongst the aftermarket and racing worlds.” The fact is, the good dampers will protect your engine, if properly matched. Choosing one should be based on your mission, your plans for the engine, and the research you do.