I have a 351/400 in my 56 F100. It was in there attached to a C6 when I got it. I would like to know if there are any guides as to what exactly it is?

I have found a few identifying marks the engine number appears to be 2A175xxx and it looks like there are casting marks that look something like an I with two circles under it, with M7 DIF E2 ? does this mean anything?

If it helps I was told that it was probably a 400 out of a ranchero or similar, but that could be wrong.

Thanks
Lee

 

The only way to tell is by measuring the stroke. There are also casting marks on the crank inside the engine.

 

Thanks Eric,

I had a feeling that that might be the answer. I just cant beleive that they would make two engines that have different internals and not mark them up accordingly externally.

I can imagine there have been many an embarrassing moment at the parts shop.

Looks like I will have to get the plugs out and a long stick.

Lee

 

They both take the same parts unless doing a rebuild and you have the engine open for that. The plugs are in at such an angle it is difficult to get a stroke reading that way.

 

Unfortunately there are no external markings that differentiate a 351M from a 400. The casting date can be a good clue to the type of engine that it is assuming it hasn't been rebuilt. Anything older than 75 would be a 400 since the 351M didn't go into production until 1975.

The casting marks you need to look for to identify the engine are on the top back near the oil press sending unit. That's where you'll find the plant codes, CF for the Cleveland Forge, MCC for the Michigan Casting Center and DIF for the Detroit Iron Foundry. The casting code for the block will be down near where the starter bolts in. On some blocks there's also a casting date there as well while on others it's up near the plant codes.

Here's a link that may help you out:

Bubba's M Block page

 

Thanks Bill,

Really usefull site. That gives me a few more pointers and things to look out for.

Cheers
Lee

 

I believe the term I would use is ALMOST no external markings. See, there is one difference between the 400m and the 351m. The 351m has 7 valve cover bolts per side. The 400 has 8. At least I'm fairly certain that's the case, let me go count mine real quick, I'll be right back...
...Yep, that's right.

 

matt what are you talking about? first there is not such thing as a 400m it's just plain 400 no M on the end of it. second the 351M and the 400 use exactly the same head so the valve covers would be the same thus the number of bolts holding them on would be the same.

 

matt 7 bolts is a 429/460 8 is a 351m/400 or 351c

 

My bad, you're right. 7 bolts is the 429, and 460.