351M heads info

[joeystang]

A neighbor sold me a set a rebuilt 351 M heads for $100. The heads are off a freshly rebuilt motor and was never used during his engine install. Question(s):

1)What are the differences between the 351 M heads vs the 351 Cleveland heads

2) Would they be any advantange replacing cleveland heads with a set of freshly rebuilt 351m heads on a cleveland motor?

 

[Tnfastbk]

Not sure it can be done:huh: Well looks like it can but not real positive things said doing a quick search.

 

[vamach1]

http://phystutor.tripod.com/stang/engines/cleveland.html

The 351M is sort of a hybrid between a 351C and the 400. The 351C and 351M have the same bore and stroke - 4.00" x 3.50" (also shared by the 351W and the 352). The 351C, 351M, 351W, and all other small blocks share the same bore spacing and cylinder head bolt pattern. Cleveland style heads were first used on the 1969 Boss 302.

The 351M has the higher deck block of the 400. This makes the engine wider and heavier than a 351C. As a result, 351M has longer connecting rods.

The 351M uses the larger 351W / 400 sized crankshaft journals. Stronger in the heavy duty truck sense, but more friction for performance applications at high RPM.

351C 351M 400 351W

Deck height 9.206" 10.297" 10.297" 9.503"*

Rod length 5.780" 6.580" 6.580" 5.956"

Main journal 2.749" 3.000" 3.000" 3.000"

Rod journal 2.311" 2.311" 2.311" 2.311"

Compression Height 1.647" 1.947" 1.647" 1.769"

* 1969/70 351W deck is 9.480"

The 351C was available with both 2-barrel and 4-barrel heads, with very different port sizes. The 4V size was the choice for high performance builders in the '70s. The 351M is available only with the smaller port, 2V heads. These are more practical on a street engine where low end torque is desired.

The 351C uses the Small Block (289/302) bellhousing bolt pattern. The 351M and 400 use the Big Block (429/460) bellhousing bolt pattern, with the exception of a fairly rare 1973 block.

All 351C blocks can be machined for 4 bolt mains.

The 351M/400 uses thinner wall block so isn't as strong after an overbore, and more prone to overheating.

351M/400 blocks cast at Michigan Casting Center before March 1977 had casting problems, resulting in cracking of the water jacket inside the lifter gallery. Blocks with date codes of 7C01 or later should be OK.

 

[joeystang]

http://phystutor.tripod.com/stang/engines/cleveland.html

The 351M is sort of a hybrid between a 351C and the 400. The 351C and 351M have the same bore and stroke - 4.00" x 3.50" (also shared by the 351W and the 352). The 351C, 351M, 351W, and all other small blocks share the same bore spacing and cylinder head bolt pattern. Cleveland style heads were first used on the 1969 Boss 302.

The 351M has the higher deck block of the 400. This makes the engine wider and heavier than a 351C. As a result, 351M has longer connecting rods.

The 351M uses the larger 351W / 400 sized crankshaft journals. Stronger in the heavy duty truck sense, but more friction for performance applications at high RPM.

351C 351M 400 351W

Deck height 9.206" 10.297" 10.297" 9.503"*

Rod length 5.780" 6.580" 6.580" 5.956"

Main journal 2.749" 3.000" 3.000" 3.000"

Rod journal 2.311" 2.311" 2.311" 2.311"

Compression Height 1.647" 1.947" 1.647" 1.769"

* 1969/70 351W deck is 9.480"

The 351C was available with both 2-barrel and 4-barrel heads, with very different port sizes. The 4V size was the choice for high performance builders in the '70s. The 351M is available only with the smaller port, 2V heads. These are more practical on a street engine where low end torque is desired.

The 351C uses the Small Block (289/302) bellhousing bolt pattern. The 351M and 400 use the Big Block (429/460) bellhousing bolt pattern, with the exception of a fairly rare 1973 block.

All 351C blocks can be machined for 4 bolt mains.

The 351M/400 uses thinner wall block so isn't as strong after an overbore, and more prone to overheating.

351M/400 blocks cast at Michigan Casting Center before March 1977 had casting problems, resulting in cracking of the water jacket inside the lifter gallery. Blocks with date codes of 7C01 or later should be OK.

Great info, Thanks

Not sure it can be done:huh: Well looks like it can but not real positive things said doing a quick search.

Well as you stated, a search on the subject doesnt seem positive...

 

[Totalled]

They don't flow as well as 2V cleveland heads, and make great doorstops.

 

[MotoArts]

M heads are basically interchangeable with 2V but have a "belly" in the exhaust port, restricting flow.

The belly is a water jacket and cannot be ground out.

 

[cobra3073]

A neighbor sold me a set a rebuilt 351 M heads for $100. The heads are off a freshly rebuilt motor and was never used during his engine install. Question(s):

1)What are the differences between the 351 M heads vs the 351 Cleveland heads

2) Would they be any advantange replacing cleveland heads with a set of freshly rebuilt 351m heads on a cleveland motor?

As to your specific questions:

1) As previously inferred, the 351M heads are similar to the 351C 2V heads. They share the same valve sizes (2.041/1.654). The main difference between the two sets of heads is in combustion chamber volume. The 351C (2V) head has an advertised chamber volume of approximately 76.2 (cc) while the 351M head's chamber volume is advertised as approximately 78.4 (cc). This means the compression ratio (when using the 351M heads on a 351C block) will be reduced from approximately 9.5:1 (351C 2V) to 8.0:1 (351M).

2) There could be an advantage in replacing the 351C heads with the 351M heads, dependent upon what was done to the 351M heads, changes made to the 351C block (i.e. pistons, rods, etc.), and the desired "outcome."

Keep in mind there are several other "issues" that should be considered if you decide on this swap, a big one being that due to the differences in deck height, you will most assuredly have to consider a change in push rod length.

BT

 

[Paul of MO]

They are OK for a street motor - With a mild hyd cam you will not have any pushrod issues. These heads are basically a bolt on swap for a cleveland.

You will have a big valve, low compression, pump gas burning engine that will make 225 to 250 hp with a 600 holley and stock exhaust manifolds. It will sound nice at idle as well.

Expect 15 to 18 mpg

It will last forever.

I have used 400M blocks and 351C 4V heads to make some affordable "Stroker" race engines for bracket racing.

http://www.tmeyerinc.com/400stroker.html

- Paul

A neighbor sold me a set a rebuilt 351 M heads for $100. The heads are off a freshly rebuilt motor and was never used during his engine install. Question(s):

1)What are the differences between the 351 M heads vs the 351 Cleveland heads

2) Would they be any advantange replacing cleveland heads with a set of freshly rebuilt 351m heads on a cleveland motor?

As to your specific questions:

1) As previously inferred, the 351M heads are similar to the 351C 2V heads. They share the same valve sizes (2.041/1.654). The main difference between the two sets of heads is in combustion chamber volume. The 351C (2V) head has an advertised chamber volume of approximately 76.2 (cc) while the 351M head's chamber volume is advertised as approximately 78.4 (cc). This means the compression ratio (when using the 351M heads on a 351C block) will be reduced from approximately 9.5:1 (351C 2V) to 8.0:1 (351M).

2) There could be an advantage in replacing the 351C heads with the 351M heads, dependent upon what was done to the 351M heads, changes made to the 351C block (i.e. pistons, rods, etc.), and the desired "outcome."

Keep in mind there are several other "issues" that should be considered if you decide on this swap, a big one being that due to the differences in deck height, you will most assuredly have to consider a change in push rod length.

BT