I've never heard of any crank breakage issues with any AMC six.
I don't know Navarro's thinking, but seeing how it ran at insane boosts it must have been for revving. Clearly with the big pump cylinders were getting filled. One assumes Barney knew what he was doing.
550hp from the original single-turbo carbed motor, 750hp from the twin-turbo Hillborn injected motor. The motor was sleeved down to 181ci (0.44" thick cylinder walls).
