I stated quite clearly, the factory nodular cranks are superior to the cast steel. Like Bogie, I do this stuff for a living. The Chinese FORGINGS are better than the factory nodular, IF you choose a good one. We've seen LOTS of balance issues with Scat cranks. Not so many with Eagle. We too, buy them in "pieces". Seldom to kits have all the correct combination for optimum performance. We generally use different pistons and bearings than Eagle supplies. Their rods and cranks are as good or better than any.
RED FLAG! Crank kits may or may not be a good idea. For a pickup truck "to get down the road", they're usually okay. For any performance application, they can be a real roll of the dice. Companies like CRI (Crankshaft Rebuilders, Inc.) and "Standard" (East Coast remanufacturers) are perfectly willing to weld up a torn up journal on a cast crank. This is bad. A casting isn't receptive to welding like a forging. It changes the surface tension, a known "sore spot" in castings. If you find one that's 10/10 or 20/20 (.010" or .020" undersize on both mains and rods), you have a good chance it's not been welded. It shold be magnafluxed before being used in a performance engine. They also usually come with the cheapest bearings known to man. Not ALL Clevite bearings are the same. They have various "levels".
Bogie's description of "internal/external" is right on the money. For those that are still confused about just exactly WHAT IS BALANCING?, here:
All pistons are weighed. The lightest one is "matched" by removing material from the others. The rods are weighed, both "ends" and "static". Again, the "light" ones are found and the rest matched. A set of rings (1 piston's worth) is weighed. The rod bearing is weighed. The piston pin and locks (if so equipped). There are two specs: Rotating weight (rod bearing, "big end" of rod, 4 gr. oil) and reciprocating (piston, pin, locks, rings and "little end" of the rod) weight. For most V8s, 1/2 of the reciprocating weight and 100% of the rotating weight are used to calculate the "bob weight". A weight made up to match a PAIR of rod/piston assemblies is attached to each rod journal. If "external", the flywheel/flexplate and balancer are attached. The crankshaft is "spun" by a motor. There are sensors in the stand that detect the "heavy spot" at given RPM intervals. Material is removed or added until the triggers are not activated. If you've ever seen a tire balanced with a strobe light, exactly the same principle. This is a simplification, but accurate. Most modern machines are computer controlled.