While external balance is the norm for 383s, internal balance may be achieved by the use of dense Mallory metal inserted into the crank's counterweights, rather than using the eccentrically weighted, external-balance dampers, flywheels, or flexplates. What's the difference? Externally balanced engines make up the deficiency in counterweight at each end of the crank, which serves the purpose of bringing the total rotating assembly in balance. However, this arrangement is not without compromise. With the eccentric weight hung at the extremities of the crank rather than at the counterweight directly in line with the piston and rod weight they are charged with offsetting, a bending movement is imparted to the crank. With a low-rpm slug like a production 400 small-block, the magnitude of this force is negligible, making an externally balanced assembly an effective approach to bringing the engine into balance. In very-high-rpm applications, however, an internally balanced engine will hold an advantage in minimizing these bending motions, which become more significant as rpm escalates. As a consolation, high-rpm race engines are more likely to hang much lighter components at the crank journal, making internal balance much more viable. On the other hand, in a typical street/strip rpm range, we'd hang our hat with the Detroit engineers and simply externally balance it and not get too hung up about it.