The Harmonic Damper or "Balancer" is an integral part of any engine. It's main function is to stop or "dampen" harmful harmonics in the crankshaft that occur while the engine is running. Imagine you have a crankshaft standing up in front of you on the shop floor. If you hit it with a hammer, it's going to ring like a bell. This is basically what happens in the engine when the explosion in a cylinder "slams" the rod and piston down onto the crank. Now if you touch that ringing crank with one finger, it will reduce the ringing, but it will take a little while. If you grab the crank with both hands, it's going to stop the ringing pretty quickly. If you and two of your buddies all grab it at once (with 6 hands) it's going to stop the ringing pretty much instantly. This is basically what a damper does. The more mass the damper has (the physically heavier it is) the better it works as far as dampening ability. However, in a racing engine, we generally want components to be light, so they will spin up faster and the engine will rev faster and make more horsepower. So even though a heavier damper will function better as far as protecting the crank, you pay for it in terms of extra weight the engine has to spin up. This is similar to the effect a heavier flywheel has on a 4 speed car. So, if you are willing to give up some dampening ability and protection for the crankshaft, a lighter damper will allow the engine to spin up faster. If you want maximum protection and durability for the crankshaft, then go with the thicker and heavier style. From the factory, Chrysler used the thinner style dampers on 383 and 440 Wedge engines, and the thicker, heavier style on 426 Hemis and other heavy duty Industrial applications such as 413's in large trucks and generators, etc. Fluid Dampers work a bit differently because they use an inner ring which "floats" in fluid. So even though they are heavy when placed on a scale, when the engine is spinning them, the inner ring floats in the fluid contained within the outer housing. So the light outer housing spins around the ring, and the engine doesn't "feel" the weight of the ring when spinning up. We have sold thousands of both fluid and elastomer style dampers for decades and have had good results with both types. Some builders prefer one and some prefer the other. We carry both types so you can decide which is best for you.