Im trying to figure out if it is a 351M of a 351C some one has installed in a 71 f100 how can I tell without taking the engine apart??

 

best way imo is top radiator hose into block vs intake on w. also fuel pump bolts vertical vs horizontal on w...

 

The two have different bellhousing bolt patterns. The C has the small block pattern and the M has the 385 series pattern. I don't know how far apart the holes should be on each, but it is an easily measureable amount. IIRC, the M also has a significantly taller deck height which would make the intake manifolds different widths.

 

He was asking about a 351C and M not a 351W.

To tell the difference:
Engine Identification (rev):
======================
351C/M/400 335 series: 8 bolts in rectangular valve covers. Timing chain housing is part of block. Thermostat housing on block. Exhaust bolt holes diagonal.
351M/400 335 series: intake is 12.7" wide the 351C is narrow.
Looking at the block at the base of the distributor the 351C will be even with the bottom of the intake manifold. With a 351M/400 there will be a ~1" high lip up to the bottom of the intake manifold.

 

thank you for the information

 

They didn't make clevelands after 72 so look for

D1AE - or D2AE casting numbers

351M's would have D7AE casting numbers.

 

actually they stopped production of the C in 74

 

so does that mean my cleveland valve covers will fit on my 400?

 

351C 351M and 400 valve covers interchange but some valve train components require tall valve covers to clear them.

 

like roller rockers, etc? is the PVC valve needed, or can i use one of those racing breather things on the valve covers.

 

Some roller rockers require tall valve covers.

A PCV valve is required on any vehicle where you want the engine to live a normal life. Otherwise deposits will form rapidly in the engine and excessive wear will occur.

 

351C vs 351M - look for a cast "fin" next to the distributor, most of the 351M/400 engines have that. Look at where the heads meet the block deck - 351M/400 deck is about 1" above the timing cover, 351C sits right on it. Look at the motor mounts if you can - 351C uses a similar mount to a 289/302/351W, 351M/400 mounts bolt to the side of the block using three bolts. As mentioned, the 351M/400 has a big (same as 385 series) bellhousing pattern. 351C has bell same as 289/302/351W.