[Wade Chamberlain]

Eric - dude, take a step back and think about it for minute before laying into somebody. The explanation that "sport" posted is the one that every ford engine book out there lists as the reason for the change in firing order. You missed the point of it all. It's not about an extra .01 seconds between firing, or fatigue. It's about the combined forces of having two cylinders on the power stroke, sharing the same crank throw, and loading the weakest part of the block.

Think about it for a minute. Sketch it out if you like. With the 154... firing order, cylinder #1 fires, then 90° later, cylinder #5 fires. #1 is only half way through its power stroke, so it's still loading the crank when #5 fires. Now you have TWO cylinders, on the same crank journal, in the weakest part of the block, both on the power stroke. THAT's the problem. Not lack of "rest" period.