dastang2 said:
they were changed to the 351 order for 1, because it was better on the bearings and 2 it is supposed to run smoother. the cam is what changes the firing order.
There's history behind the change to the 351W firing order. The 302 came out in 1968, and was offered with a 4bbl and 10.5:1 compression. It was rated at 250hp, if I recall.
Anyway, the BOSS 302 soon took its performance place in 1969, followed by the 351C in 71, and the regular non-boss 302 (I refer to the standard 302s as 302W, to clarify) was placed in low-performance/light truck applications from then on. The performance camshaft grind for the 302 was discarded over the years, and then in 1982,(81.5?) when the "HO" 302 was released, Ford had no performance 302 camshafts for the motor. So they dug into their 351W Marine parts bin, and found a suitable camshaft. Thus, the HO 302s were born with the camshaft, (and firing order) of the 351W. Ford never changed back to the older 302 firing order, probably for simplicity sake.
Now the 351W, with its FAR greater recipricating mass, required(or so Ford engineers figured) the altered firing order to relieve stress on the #1 main webbing. (the old 302 "15426378" firing order hits 1 and 5 cylinders at the same time, which is putting strain on that #1 main journal)
How necessary this firing order change was in the 351W is unknown, because they also increased the main bearing size of the 351W to 3", which ended up being TOO big. (that's why NASCAR 351s have the smaller 351C journals)
I've built 351Ws for friends using whatever camshaft I happened to have laying around, and for this reason, I have installed 302 cams in them. (The 351Ws with 302 hearts have survived without issues as of yet!)