What exactly is done when a block is balanced and blueprinted?

 

Balancing is just that. The rotating assembly is disassembled and everything is weighed. All the con rods are brought down to the weight of the lightest rod. The same thing is done to the pistons. The combined weight of the con rod and piston assembly is then transfered to the crankshaft, and flexplate with balancer if the engine is externally balanced, The crankshaft is then balanced to match the new adjusted weights by added or removing weight. Whenever you change pistons or con rods, the engine should be balanced.

Blueprinting is a little different and not always done. What blueprinting does is puts all the engine tolerances to an exact number. If they say that crankshaft endplay can be within .001-.005, you adjust it to .003 so it's right in the center of the tolerance. The gains reached from blueprinting don't justify the expense of doing it. Just as long as everything is within the tolerances, it will work just fine.