The rotating assembly of your typical high-horsepower engine creates some serious vibrations every time it goes through its four-stroke cycle and all of that is delivered through the crankshaft. To keep those torsional vibrations from ripping the engine apart, harmonic balancers were developed and attached to the snout of a crankshaft. In this article, we’ll speak with J.C. Beattie Jr. from ATI Performance Products and James Stray from SAM Tech, about how harmonic balancers have changed and why selecting the right one is so important.

Balancer Basics

The engine in your street car uses a basic elastomer style of harmonic balancer to control the vibrations created while the engine is running. These balancers will use a solid piece of metal for the main hub, and have some type of material attached to it for balance. A balancer like this is designed and “tuned” to function within a certain RPM range so it can control the vibrations created by an engine — when you go outside of that range the balancer will fail. This is why you have to upgrade balancers when you start to create more horsepower with an OEM engine.

While these conventional single-strip elastomer dampeners work well in a low-RPM environment, they don’t last long in a high-RPM environment, like the one you see in a racing application. These balancers only have the inertia weight attached to the crank hub with a rubber insulator — this allows the ring to move around in relation to the keyway on the crank. As that happens, it will become imbalanced and that will cause damage to the engine.

High-performance harmonic balancer designs have undergone small changes as companies have made refinements. There are several different types of balancers on the market; some are a viscous-style, filled with silicone fluid. The fluid-style balancer has an outer housing that holds the silicone fluid and an inner inertia ring. These two rings move in and out of phase, and as this happens the inner ring moves through the silicone causing shear, and that’s what eliminates the torsional vibrations.

James Stray is an instructor at SAM Tech in Houston, Texas and he’s seen the evolution of balancers during his time working in the high-performance industry.

“It’s been interesting to see how balancers have transformed over the years as companies try different things. The innovation of modern dampers has changed a great deal, and we are now seeing fluid-filled and multi-stage elastomer designs. With increased design technology we are seeing more stability at higher RPM levels,” Stray says.

“For ATI, not much has changed with our balancers. We have made some updates and adaptations of the same design that Jim Beattie, Sr. came up with many years ago. – J.C. Beattie, Jr., ATI Performance Products

ATI developed its own type of balancer known as the Super Damper that can be rebuilt and tuned based on the engine it’s bolted to. The Super Damper has an outer shell that’s made from either steel or aluminum that acts as the housing for the inertia weight inside. These inertia weights are made from steel and will vary in size depending on the application.

This diagram shows how much goes into an ATI Super Damper versus your typical OEM style harmonic balancer.

The elastomer O-rings that are a part of the inertia weights are what really do the work with this type of balancer. They can be tuned with the outer O-rings controlling the high RPM crank twist, while the inner rings are what ultimately controls the middle RPM range. What makes this style of balancer great for racers is that it can be rebuilt as needed.

You can also have the balancer re-tuned if you make any changes to your engine so it will work with the new combination. This is especially helpful for those with a naturally-aspirated engine, because they might make a change with the engine that allows them to rev to a much higher RPM; when this happens you must adjust the balancer to account for the new stress level on the crankshaft.

“To tune the Super Damper on such a wide range of high-performance engines, we have nine different inertia weights, from 1.2- to 30.5-pounds. Then we have Elastomer O-rings in 40, 50, 60, 70, 80, and 90 durometers available to match a specific inertia weight to a given engine size, rotating components, horsepower, and RPM level to eliminate torsional twist of the crankshaft,” Beattie explains.

The How, Why, And What

A crankshaft rotates thousands of times per minute and as this happens it’s generating a lot of force. The crankshaft twists back and forth during this process and is measured in degrees of twist peak to peak. According to Beattie, this twist is what breaks parts and reduces horsepower if it’s not addressed.

“A damper’s job is to absorb and counteract as much of the twist as possible. With the right damper on your engine, the majority of the twist can be eliminated. However, with the wrong damper, virtually all of the twist can remain or even be added to. A damper’s job is to rebound the recoil of a spring. In this case, the spring is your crankshaft twisting, and when it tries to rebound past its natural state, that is when the damper needs to counteract and stop it,” Beattie explains.

The dampers must be SFI-certified and designed to operate in the correct RPM range and power level sourced from a reputable supplier. – Jimmy Stray, SAM Tech Instructor

In any high-performance application, especially a naturally-aspirated one that will spin to a higher RPM level, it becomes vital to have the right harmonic balancer. As the RPM climbs as the crankshaft spins, the torsional vibrations grow exponentially.

“In a nutshell, harmonic dampers help to reduce the torsional stresses generated by the linear to rotational motion of the engine. Using the correct damper is vital to reduce the damaging harmonics generated in any engine, but especially so at today’s higher horsepower levels. Reducing the torsional stress is a huge benefit in the sense that we are able to push the structural limits of the engine much further,” Stray says.

Not using the correct harmonic balancer can cause catastrophic crankshaft failure due to the stress of torsional vibrations.

So you know how the balancer protects your engine and why you need one, but do you know what to look for? Each engine has different balancer requirements based on its size, accessories, and application. The weight of the balancer needs to match the engine so it can do its job of making sure the torsional vibrations are kept in check.

According to Beattie, there are some other things you need to keep in mind when selecting your harmonic balancer.

“SFI approval is important — you want to be sure you have a balancer that’s approved for safety reasons. You should also look at the design; the Super Damper and others will never allow the timing marks to rotate on the inner part of the damper. A good keyway is important, along with quality fasteners to make sure the damper can deal with the extreme environment it’s put in. You just want to select a high-quality damper because its job is very important.”

A harmonic balancer is a part that you don’t want to overlook or not invest in when you’re building an engine. If high-RPM is in the future for your engine, the right balancer becomes critical if you want it to perform and last.