[Jay S]

If I have something here wrong feel free to correct me. Crank materials Arma steel is suppose to have a tensile strength of 105,000 psi, and a yield strength of 85,000. Nodular iron used in N cranks and 103’s should be pretty close to that, certainly would not be higher.

A factory forged crank is usually around 110,000 tensile strength, 10 series metals, but with more elasticity than nodular or Arma. Not that much stronger than nodular but more resilient to flexing. Which is due largely do to the improvement in grain structure over the N cranks. The grain structure on modern Chinesium N cranks is generally pretty terrible. Some of the factory forged are also forged in twist forgings. On those each throw they have to turn the forging die, it adds some internal stress in the crank versus non twist. Not sure what an old forged Pontiac crank would be? I think they may be this category.

Most of the aftermarket cranks are 4340 non twist forged cranks, around 140-145,000 psi tensile, and 91,000 yield. The non twist die are suppose to make it more resilient yet because they are forged in one shot from different directions. The further apart the tensile and yield are represent more ability to twist and better memory. You can compare the numbers, it is quite a difference which typical forged. We can praise a old Pontiac N crank all we want or even factory forged, but the strength is really not that close to a 4340 non twist.

A billet is SUPPOSE to be 160-165,000 psi tensile strength with more flexing resilience to all the others, still in the 90s yield? A lot of that is the extra yield combined with the steel’s grain running in the same direction combine to let it twist more. But the long term longevity, fatigue life, is notably less than the 4340 non twist crank at some power levels. The grain structure of the 4340 non twist has some advantages. Some argue it is still better depending on who you talk too, there are definitely different levels of Billet steel. Steve’s crank should not have broke. X3 they stopped the off shore for a reason.