Can you post a picture of it? A 400 is pretty easy to spot, however it's almost impossible to visually distinguish from a 351M. Everything between the two motors is interchangeable except the crank and pistons, since they're the exact same engines, just different strokes. I'm not sure if it's possible to accurately measure the stroke in this case or not - otherwise the part number on the crankshaft would tell. This all assumes that the original valve cover sticker is gone - if not, then this is a no-brainer.
If you pull a spark plug, stick a dowel into the cylinder and turn the crank, measure the stroke, the difference between the highest point and lowest point. If it's 4" it's a 400, if it's less, it's a 351M. That is, as long as the engine block is a 400/351M engine block and someone didn't swap in something different before you got it. Plus, if the valve covers are original, then one of them should have a label on it saying what it is.
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One way is to take the number off the block and google it. The engine block# should pop up as a Ford 400 engine if the engine hasn't been swaped out.
Casting numbers on blocks are WORTHLESS for ID'ing the size of the engine or what vehicles it came from, ditto cylinder heads. Casting numbers are foundry marks only, cannot be cross referenced to Ford part numbers.
1977/79 F100/350 & 1978/79 Bronco: The same block casting numbers used on the 400 were also used on the 351M: D7TE-6015-AB, -A1B, -A2B.
351M/400's share the same bore (4.00"), the stroke is different. Stroke: 351M = 3.50" / 400 = 4.00"
It's almost impossible to tell a 351C from a 351M, or 400, because all look identical. Only the original carb and dizzy ID tag numbers are different.
Originally there was an engine ID tag bolted to the coil bracket, or intake manifold, but most of these are missing by now.
351C/351M/400: 8 valve cover bolt holes per side. There is no timing cover per se, just a flat plate.
The fuel pump bolts to the left (drivers) side of the block. Its bolt pattern is at 12 & 6 o'clock, the only fuel pumps to have this bolt pattern (all others are at 3 and 9 o'clock).
Bill / Retired Ford Parts Manager / SoCal Chapter Member / Part number research: 1928/2001 trucks & 1928/89 passenger cars.
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