351W F.O. changed to 289

[EricF]

I am going to try to be more tactful, but it is hard………


Originally posted by 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.

Lets create a Scenario

Engine is spinning at 6000 RPM

Which is 100 revolutions per second

It takes 2 complete revolutions for all 8 cylinders to fire, a cylinder fires every 90 deg.

Ergo, when a Ford 351W is spinning @ 6000 RPM each cylinder fires 50 times per second

50 times per second * 8 cylinders = 400 cylinders firing per second

This means that the time interval between each cylinder firing, at 6000 RPM, is .0025 seconds.

So with the 1,5,4,2.… firing order, cylinder 1 fires, then .0025 seconds later, cylinder 5 fires.

With the 1,3,7,2,6,5.….. Firing order, cylinder 1 fires, then .0125 seconds later, cylinder 5 fires.

With either firing order, there is still a pause between each cylinder firing, and cylinder 5 will eventually fire after cylinder 1.

So you are saying that the extra .010 seconds that the front main gets to “rest” before cylinder 5 fires, with the 1,3,7,2.… firing order, over the 1,5,4... Firing order, is going to make a difference with the fatigue of the front main in your “not a good situation” scenario?

Or what about a twin V configuration? For that matter, Is that also “not a good situation”


Good Lord, where do you come up with this stuff? Seriously, did you just make this up? Or after you “sketched out the firing order on a piece of paper” the entire cyclical stress dynamics of the rotating mass just came to you?

When an engineer what’s to analyze cyclical stress failures, they should just throw away all of their S/N curves & finite element analysis & just hire you instead, you could sketch it out on a piece of paper & figure it out, without going through any of that engineering nonsense no less.

Do you have any data that shows a difference between the high cycle fatigue of the front main by varying between the two firing orders?