>I presume that is because you would weaken a forging by removing material
>from the surface.
Actually in some situations removing material from a forging helps. Look
at the additional price of "polished connecting rods" Here you take the
flash that was formed by the pressing, and smooth it down to a fine
surface. This is a good place for cracks to form on connecting rods and
the polishing lowers the chance. Also forged cranks when prepped at a good
machine shop will get the same treatment.
>Does that mean replacing a cast crank with a forged one would force you
>to balance externally?
The manufacturers are going to external balance (Chevy went this route in
1986) because they can make the crank with much much smaller
counterweights, and adding mass to the dampner and the rear plate is much
cheaper.
But to answer your original question (and to quit rambling) no, a forged
crank can be made with the same weight as a cast, or whatever weight you
want within reason. Cranks from one engine to another (318~340~360), well
that was up entirely to the original engineers.
>Are billet cranks REALLY the way to go for an engine whose block was
>designed for an internally balanced crank?
Blocks do not care about internal and external. And forged are better to
get than billet. The grain structure on a forged is more continous since
it is forged. A billet is cut from a solid blank of steel, the grains stop
wherever the cutting stops, with most at right angles (bad) A billet is a
neccessity if a forged is not available with your specifications.
Regards
Nicholas
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