How do I differentiate a 351M and a 351C easily?

 

Usually - the 351C cylinder head has a 2 or 4 cast in its outer corner next to the valve cover, the 351 is blank - usually.

 

The bolts holding the fuel pump on a 351 cleveland are vertical on other 351's like windsors they are horizontal.

 

i had a 351M the only thing i could find to tell the difference was the sticker on it, but the heads were bigger im pretty sure

 

A 351M uses the big block bellhousing bolt pattern where the 351c has a small block pattern. The big blocks stretch 7 1/2" between the top two bell bolts (at the flat top), the small block is only like 5".

--Mike

 

Count the valve cover bolts: 6 bolts: 351W, 8 bolts: 351C
Windsor engine characteristics
-thermostat housing bolted to the front of the intake manifold
-351W's have intake bolts 90 degrees to the ground
-351W's have evenly spaced exhausts aimed 90 degrees from length of head Comparison of the 351C vs. the 351W fuel pumps
- The 351C bolts are verticle, 351W are horizontal

Cleveland engine characteristics
-the thermostat housing is on the block extension which contains the timing chain
-351C manifolds are dry, no water passages or thermostat housing....thermostat housing goes into the front of the block
-The Cleveland has the small 300/302/351W bell housing pattern.

 

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.
351W/302/5.0L 6 bolts on trapezoidal valve covers. Thermostat housing on intake. Exhaust bolt holes horizontal.
429/460 385 series: 7 bolts in rectangular valve cover
352/360/390/427/428 FE series: Intake goes under valve covers.
-There are other indicators but these are enough to distinguish engine families.


Both the 351C and 351M are 335 series engines. You can find more information in the 335 series engine forum.

 

as mike said the bell is different and the 351c takes 302 mounts.