[sport]

The 351W "1,3,7...." firing order more evenly distributes the firing load on the mains. The old 289/302 with its "1,5,4..." order had the #1 and #5 cylinders firing one after another on the front main which was double stressing the weakest part of the block. Not a good situation, so Ford revised it back in '69 when they created the 351W.

If you trace the firing orders out on paper, you'll notice how the 1,3,7.. order puts the stress on the center 3 main webs taking it off the front where the block is weaker.

The cam companies might have data showing that the old 289/302 firing order makes more power. But in a high output 351W based engine, Comp Cams told me to use the regular 351W firing order.