Prowler V6

[Greg Hermann]

>    The reason for using a forged crank as compared to a cast one is
>actually more a matter of "flexability." with a cast crank the material
>isn't as flexable as the forged counterpart.

Actually--

Steel has a significantly high modulus of elasticity than cast iron, both
in tension and in shear.
Which means that a steel crank is, in fact, quite a bit STIFFER than a cast
one. -It does NOT flex as much!-- The steel is, however, much more DUCTILE
than cast iron, even if compared to so-called "ductile" (or nodular) cast
iron.  "Ductile" and "brittle" are pretty much antonyms in this context.
This means that a steel part will deform and "tear" far more than an iron
one will when it actually fails, even though it takes a much higher level
of stress to produce a failure in a steel part.

A steel part also has FAR greater resistance to the initiation of cracks
when subjected to alternating  tensile and compressive stresses than an
iron part does. In fact--steel has a well defined "endurance limit" of
stress under fatigue failure inducing alternating stress conditions, and
cast iron does not.

A cast part usually will usually absorb vibrations far better than a steel
one will--which makes the need for more sophisticated, expensive vibration
dampers on cast production cranks less pressing than it is on forged steel
cranks. Witness the fact that if you tap a cast crank with a hammer, it
gives a clunk sound, while a forged crank will ring like a bell.

Because a steel crank is actually much stiffer than a cast crank, your
blocks would probably stand up to significantly more HP if you ran forged
steel cranks in them---because a stiffer crank would not impose nearly as
much strain (deflection) onto the bearing webs! (In a case like the block
failures you are getting, strain (imposed deflection) is the CAUSE of the
stress, not the other way around!) Of course, you would be wise to run a
Fluidampr on a forged crank in this application because of a forged crank's
decreased capacity to damp out (absorb) torsional vibrations compared to a
cast crank.

Regards, Greg