There’s a lot of time, precision, and ultimately money that goes into building a high-performance engine. The old saying about how “speed costs” is permanently etched in the back of every engine builder’s mind, and they’re reminded of it every time they look at a parts catalogue. What that saying really implies though is that there are some components that simply can’t be overlooked. And that’s not about producing horsepower: it’s about the reliability of the entire assembly, especially at the bottom end.
The extreme twisting and flexing loads on high-performance crankshafts generate torsional vibrations that can lead to resonance. It’s the harmonic frequency of that resonance, however – or more accurately, its amplification after reaching a certain point – that can lead to an engine literally pounding itself to pieces. Ultimately, if you’re planning on building a high-performance engine, you need to make sure that reliable resonance prevention ranks just as high on your shopping list as all the other parts. And it only takes one simple component to keep you from seeing just how much speed could end up costing you.
Let’s be honest: when a big, torquey engine flexes its muscles, preventing all the vibrations created by rotating forces, violent combustion cycles, and rising and falling RPMs from becoming dangerously synchronized is no easy task. That’s why for high performance engines in particular, it’s absolutely essential that appropriate sized and rated harmonic dampers are used to absorb these vibrations. Dampers (commonly referred to as balancers) are attached to the crankshaft at the front of an engine, and rely on either mechanical or dynamic mediums to essentially soaks up unwanted vibrations and transfer them away from the engine in the form of heat.
Bolt-on pulley assemblies for power-driven accessories, as well as turbos and superchargers are attached ahead of the damper, so they’re typically hidden from view on most engines. And although they’re bolted to the crankshaft, they aren’t bolt-ons in the traditional sense, nor do they add any additional horsepower. What they’re incredibly efficient at doing, however, is:
- Reducing dangerous crankshaft deflection that could ruin the main caps;
- Preventing excessive main bearing wear;
- Eliminating destructive stress on connecting rod bolts;
- Reducing the risk of timing chain and valvetrain damage; and,
- Preventing flywheel or flexplate damage.
For race-prepped and high output engines, only a high-performance harmonic balancer is going to eliminate the power-robbing vibration that can lead to premature parts wear, or even cause a crankshaft to fail altogether. It’s the peace of mind that every engine builder wants.
Balancers are manufactured in an array of offset thicknesses and diameters to match an engine’s intended use, as well as a range of other very specific criteria that include, but isn’t limited to:
- Engine displacement;
- Anticipated engine RPM and power curve; and,
- Anticipated horsepower rating.
Suffice it to say, top balancer manufacturers don’t leave anything to chance when it comes to producing their high-performance balancers, but it’s with very good reason. They know that a heavily bored and stroked engine that’s grinding out healthy amounts of low-end torque is going to experience completely different torsional stresses than a smaller displacement, high RPM screamer will. This is especially true for engines running a racing harmonic balancer, where having a crank trigger or a drive pulley integrated directly onto the balancer will affect how much damping mass is needed.
Ultimately, a harmonic balancer can’t do its job if it doesn’t match the engine’s specs. And that’s why builders first have to know what their engines are capable of, in order to determine which balancer’s best suited to keep everything rotating smoothly.
Although there are several different types of engine balancers, there are 3 main types used on high performance and full race-prepped engines. They’re all designed to mate to a crankshaft in the same manner, though: by press-fit alignment with the keyway shaft that’s machined in the nose of the crankshaft. And once they’re on, they qualify as full-fledged parts of the powertrain.
Elastomeric balancers are the simplest and most widely used type of high-performance harmonic balancers, and are constructed of 3 main parts: a high carbon steel main hub that mounts to the crankshaft, an elastomer anti-vibration rubber damper that goes around the hub, and an anodized aluminium outer inertia ring.
Instead of a solid rubber damper, fluid balancers rely on a viscous-filled fluid chamber that’s laser-welded between a 2 part main steel hub and outer inertia ring assembly. These balancers cost more than other types of balancers, and may experience fluid breakdown after prolonged periods above 300°C.
Friction type balancers use a 2 part aluminium enclosure surrounding a wet-type, spring-loaded clutch pack assembly that absorbs vibration by slippage. There are a lot of moving parts in these balancers though, and require servicing every 1-2 years even on moderate power increases.
Elastomeric balancers are the hands-down preference for most builders, but choosing the right one isn’t an arbitrary decision. Choosing one that isn’t matched to an engine’s characteristics can be just as detrimental as not having one at all, and engine builders need to understand that harmonic balancers aren’t just accessories: they’re genuinely part of the core build.
The Smart Choice
As tempting as it may be, make no mistake: if you’re considering building a high-performance engine, reusing an OE balancer, regardless of the factory performance specs of the donor engine, isn’t an option. The risks are simply too great for the following reasons:
- Degradation. OE balancers are overwhelmingly elastomer types, and factory-grade rubber degrades after hundreds of thousands of kilometres of use.
- Power. OE balancers are only designed for a very tame and specific horsepower range. Forcing it to go outside that docile range will shred it almost immediately.
- Safety. If you’re building a competition engine, you’ll very likely need an SFI 18.1-approved balancer to compete. High-performance models are compliant.
In short, trying to take a shortcut with a balancer can quickly become a very costly excursion. Using an OE balancer on a high-performance engine won’t just destroy it: it can wrench the outer inertia ring completely off, turning it into a high RPM projectile. Investing in a new balancer that is designed strictly for a high-performance engine is the smart choice.
The Final Word
At the end of the day, there are a wealth of alternatives available when it comes to picking out a high-performance balancer, but you’ll quickly realize that selecting the right one has nothing to do with whether it correctly fits the engine, but rather, how well it’s suited for the engine. If you’re in the market for one for a high out or racing build, be sure to deal exclusively with a retailer who genuinely knows about harmonic dampers, and take the time to accurately convey to them the specifics of your build. It’ll be time well worth the effort; because even though speed costs, when it comes to reliability, it also pays a very impressive dividend.