I just bought a 1980 F150 and I don't know what engine it has. It is not the original engine, It is a crate motor for a stock car or something like that(what the guy said). According to the firing order I think it is a 351 or 400. I found a number on the bottom of the block, but can't decode it. DIAE-6015-A2C Can you?

 

charlez,

The D1AE number is for a 1971 400. Since the 351M and 400 use the same block, the block ID alone doesn't tell you much, except where the block came from, especially if the engine was rebuilt.

To determine whether you have a 351M or 400, you need to check the casting marks on the crankshaft. They are located on the first counterweight or the first throw of the crankshaft. Unfortunately, this requires dropping the oil pan.

Casting marks for the 400 crankshaft are 5M, 5MA, or 5MAB. Casting marks for the 351M crankshaft are 1K or 1KA.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

Another way to possibly I.D., is to take a piece of wire (stiff) and run one piston from top to bottom and measure what the stroke is (thru the spark plug hole), 3.5" or 4", this will then give a clue to the displacment. The 351M has a 3.5" stroke and a 400 has the 4" of stroke. Both have a 4" bore. Also, I don't think the 351M was produced in '71, not sure though. These are interchangable as far as making one out of the other (smaller to bigger and bigger to smaller), only thing needed is crank and pistons. Hopefully, someone can help out a little more with when they actually started producing 351M's!