An engine’s harmonic damper, by design, does not move from its installed position, and does not “make power,” yet so many words have been written about these engine components that are basically just a big mass of weight that hangs from the end of your engine’s crankshaft. As an engine fires each cylinder, the firing pulse is applied to the crankshaft in the form of torque, and in the process the crankshaft deflects under this pressure. A harmonic damper is designed and tuned to counteract the worst of the crankshaft’s vibrations.
There are a number of different designs on the market, but the most prevalent is the elastomer-damper design. In an effort to gain a better understanding of how these types of dampers work, we caught up with ATI Performance Products’ JC Beattie, Jr., and he was happy to give us an education. According to JC, somewhere around 98% of your passenger-car and light-truck vehicles use an elastomer-type damper from the factory, while over-the-road trucks are 98% fluid-type dampers.
When someone rebuilds an engine to give it more power, changes the heads, the cam, puts headers on it, the stock damper then becomes no good. According to Beattie, Jr., “The OEM damper has been tuned to the frequency where the engineers feel the engine will spend the majority of its life. For example, if they put the 5.0L V8 engine into a Mustang versus an F-150, the damper will be tuned differently. The engineers can assume that the pickup truck will spend the majority of its life in the lower to mid-range RPM band, while the Mustang would be expected to spend the majority of its life in the mid-to-high RPM band – that damper is designed to work at the given horsepower and torque levels – and if you think about it, how else could the OEM’s handle it?”
How It’s Made
Construction of the ATI Super Damper is simple yet elegant – there is a hub that works with an interference-fit to the crankshaft – typically in the .0007-inch range, meaning that you’ll need the proper damper installation tool to install one. ATI can install as many as four keyways into the hub if you need them.
Then you have the inner shell, the inertia weight that incorporates the elastomer o-rings, and the outer shell. Other brands of elastomer damper may have an inner and outer metal ring that has had the elastomer material forced between the layers to bond them together while it cures, rather than the rebuildable style of the ATI damper.
Some Super Damper applications combine the hub with the inner shell for packaging reasons, and certain applications can use an aluminum outer shell for weight reduction. Beattie Jr. says that steel and aluminum damper sales run about even, even though their most popular application by far (big block Chevy) is steel. Various applications also use pins instead of keyways to retain the damper, as the original equipment part may have used an interference fit rather than a keyway for damper retention.
How It Works
Before we get into the discussion about how the damper absorbs the harmonics of the engine, it’s important to understand a few definitions.
- Frequency: a vibration at a specific number of cycles per second (measured in “hertz”)
- Order: a specific multiple of a basic frequency
- Damper: a device to dissipate energy
To better understand crankshaft twist and what we are trying to combat with a harmonic damper, think of a swing set. When you get on the swing and go in one direction, you’ll always go backward about the same amount – you don’t just stop in the middle. The crankshaft undergoes the same type of force when the combustion events are trying to turn it into a pretzel.
Since the crankshaft is basically a piece of high-strength steel, it acts as a nearly perfect spring. The damper, bolted to the free end of the crankshaft, helps to – yep, you guessed it – dampen the oscillations caused by combustion. A typical V8 engine at full power with no damper will eat itself within minutes, yet one equipped with a proper damper will yield millions of revolutions with ease.
Basically, you can think of a damper as a shock absorber for the engine. They are tuned to work at the specific frequency of a particular engine – its worst frequency – to absorb those vibrations. Beattie, Jr. described the damper’s internals and their function, and what he means by “tuning” the damper.
“If you look at the cutaway of our damper, we have a smaller-diameter ring on the inside (hub side), and a larger-diameter ring on the outside (outer shell side). I can put two different types of rubber in there as well, we use the softer material on the inside to tune the bottom and middle range, and then the harder elastomer on the outside takes over as the engine RPM increases – we use it to keep controlling that twist. Our damper also has a single ring that sits against each face that works to lock the inertia weight against the outer shell,” he explained.
One of the positives to working with an elastomer-style damper is that a much wider range of engine frequencies can be tuned out of the harmful range.
The movements permitted by the ID and OD elastomer are how we control the RPM harmonics. – JC Beattie Jr.
Beattie explains, “98 percent of the dampers as supplied off our shelf don’t need tuning for your particular combination or have already been tuned to your engine and are on the shelf that way. Extreme race engine dampers are handled on a case by case basis. Engines turning over 8,500 rpm on a routine basis, or running a 24 hour endurance race, or producing over 3,000 horsepower, are all engines where we like to know what the damper needs to do so we can adjust the elastomer O-rings to make it perform the best under the engine’s running conditions.”
Back in the 1970’s, General Motors engineers determined that the third order harmonic is the one that is most detrimental to the crankshaft and bearings in a gasoline internal combustion engine. “What would make sense in a V8 engine would be the second and fourth orders, the second because the camshaft is turning at half the engine RPM and the fourth because there are four power pulses per revolution. But in the real world, they don’t matter,” Beattie, Jr. explained.
In his experience, tuning the third order harmonics out of an engine will provide the most gain, both in engine longevity and horsepower improvement. He explained further, “I will take a damper that has twice the fourth order harmonics as long as I can make the third order low. If I get into an engine that has three degrees of fourth-order twist, peak to peak, I can go from no damper to the biggest damper, and it might change a half a degree either way. But if I have three degrees of third-order twist, and I can reduce it to one degree by tuning the damper, firstly, I’ve changed the twist way more than I could make a difference in the fourth order of harmonics, but secondly, I can pick up somewhere around 20 horsepower by controlling the motion in the third order.”
How Big Does it Need To Be?
Damper dimensions also need to be sized properly to the engine, Beattie says. “It’s like a clutch – a seven-inch clutch will take this horsepower, and a ten-inch clutch will take that horsepower. You can put too small of a damper on too large of an engine and vice versa. We used to have a small-diameter, lightweight damper in our big-block Chevy line but we’ve been phasing them out, just like I won’t sell a six-inch, two-ring, three-pound damper to someone for a Pro Stock engine – it’s just not correct.” In most cases, the more horsepower and RPM you are looking to turn, the larger damper you are going to need.
Of course, in some applications you are limited dimensionally on the size of the damper, and in those situations compromise is required. “In those applications I’m stuck with X amount of inertia weight and we have to try to come up with a rubber combination that will allow the damper to perform at its best. Or sometimes we’re in a situation where the damper needs to live for a 24 hour race but the soft rubber I need to make it work effectively won’t last for that time period under the conditions. It’s all about optimizing for the operating conditions,” Beattie, Jr. explained.
What about Safety?
Every damper design that carries the SFI Foundation’s 18.1 spec has undergone a rigorous testing process to ensure that the damper will hold together even when its operating conditions well exceed its initial design parameters.
According to the spec, The damper shall be driven to a rotational speed between 12,500 and 13,500 rpm and maintained at that level for one hour. The test shall be considered successful if no part becomes loose or separates from the damper during the rotational test. Since none of us are running anything that will come remotely close to spinning 12,500 RPM for an hour’s duration, the specification includes a high margin of safety.
A harmonic damper is not a complicated component, yet it can be difficult from a visual inspection to tell whether one is still performing up to par or not. One of the easiest ways to tell if your stock-style damper is damaged is to check whether the engine timing is off – it’s easy to see when the damper is sitting at 60 degrees of timing advance and the engine’s locked at Top Dead Center. If that isn’t the case, Beattie, Jr. also suggests inspecting the rubber where it is sandwiched between the damper halves. In most cases, the ring is around 1/8” wide, and if it’s failing it will start to crack or peel away. The external condition is also a good indicator of how the material looks on the inside of the damper.
ATI’s research has shown that one of their aluminum shell dampers on a race motor will try to fail or crack the shell somewhere over fifty million engine cycles. To put that in perspective, that’s 26 complete NASCAR weekends. A drag racer or street guy would never do that in their lifetime. You have to figure that a NASCAR racer is running from 6900 rpm to 9800 rpm for three million engine cycles over the course of a weekend.
We will certainly recommend a steel hub and dual keyways on any application running more than ten to twelve pounds of boost. – JC Beattie Jr.
One of the persistent issues with many supercharger applications for street-going vehicles is the amount of force they can put onto the crankshaft and harmonic damper as a result. Beattie, Jr. came through with a couple of tips that the ATI team will recommend (depending on application) to help your blown machine to live a longer life.
“We’d definitely recommend an aftermarket damper bolt – we don’t want to try to use a grade 5 front bolt. On the damper side, it always goes to horsepower and RPM – any way you look at it whether you’re naturally aspirated or blown, you’re still making the same amount of horsepower whether you’re doing it with lower compression and boost, or higher compression and camshaft – they are really pretty close,” he said.
And just because it’s cool, check out the video below.
To sum it all up, the explosive forces that are acting upon your crankshaft four times per revolution can turn your crankshaft into a giant tuning fork. The elastomer-style harmonic damper does a great job of counteracting those vibrations and ensuring that your engine bearings don’t turn into shavings in the oil pan.