All of the above are signs of unchecked crankshaft harmonic vibration in a race engine. Usually, the above symptoms go hand in hand with a non-functioning damper on the nose of the crank or when a simple aluminum hub is installed in place of damper.

And one more thing to consider before we go on to other things: that lump (the damper) that hangs off the nose of your engine is not a balancer. In truth, it balances nothing. The main purpose of that big hunk of metal out front is to absorb harmonics. Harmonics and balance are two decidedly different things.

OPERATIONAL RANGE

The operating range of an engine along with the speed at which an engine accelerates can have a profound effect upon the damper requirements. Some dampers are "tuned" to operate at a specific RPM level. That's fine for an engine that runs at a constant or relatively constant speed (a good example is a diesel highway tractor with a dozen or more forward gears), but if the engine is accelerating and decelerating over a wide RPM range (as in a drag race application), then frequency tuning becomes troublesome.

Case-in-point is a widely publicized test run by Katech for General Motors. Four aftermarket dampers were tested on a 427 cubic inch small block (4.125" bore X 4.00" stroke). From 3,112 RPM to approximately 6,500 RPM, none of the dampers twisted the crankshaft more than 0.6 degrees. But after 6,500 RPM, the test proved revealing: crankshaft twist increased by a considerable margin in three of the dampers. At 7,893 RPM, the one damper showed 2.0 degrees of crank twist. Another showed 1.7 degrees of twist. Yet another showed approximately 1.25 degrees of twist. Finally, the last damper, which was an ATI model similar to the assembly shown in the accompanying photos showed 0.28 degrees of crankshaft twist.

The point in outlining the above exercise isn't to compare dampers. Instead, it goes to show that crankshafts definitely do migrate. They're not immovable objects. They do twist. And in some cases, more than others.

WHAT MAKES A DAMPER TICK?

What makes a damper such as this ATI model tick? Basically, it's a complete re-think of the proven elastomer damper configuration. Elastomer dampers have been in use for many years by Detroit. These designs are good at what they do, but conventional single strip elastomer dampers are, for the most part, not rebuildable. Typically, a stock damper has an inertia weight with a rubber insulator pressed to the crank hub. By nature of the design, this means that there is a possibility of the ring moving in relation to the hub. If the weight doesn't fly off (that's why SFI-approved dampers were mandated in the first place by the major drag race sanctioning bodies), there is still a chance that the timing marks will be lost in relation to the crank key way.

According to ATI, during the manufacturing process of an OE damper, it is impossible to maintain the concentricity of the inertial ring to the hub. The ring must be machined after it is pressed to the hub then balanced after machining. When it comes loose, imbalance can occur. In contrast, the ATI Super Damper employs a combination of 70-durometer o-rings and a unique, full-captured inertia ring to dampen harmful crankshaft vibrations. This design configuration allows the damper to actually function as two dampers in one given diameter. This accounts for the absorption of twist over such a large RPM range (racers have used the Super Damper in RPM ranges exceeding 9,000 RPM) -- especially when the engine is accelerated or decelerated.

The ATI damper is an elastomer configuration (just like many OEM dampers), but there's a "twist". The elastomer is physically captured in the design. It also relies upon a series of 70-durometer o-rings to help control crankshaft vibrations. The unique design allows the damper to actually function as two dampers in one. Testing by General Motors has shown that the ATI damper is very efficient when it comes to displacing crankshaft twist. By the way, this 7.0-inch configuration only weighs 8.95 pounds, ready to race and that includes approximately 4.5 pounds of inertia weight.