Hi can someone please explain or tell me the difference in the ford 400 and the ford 351m? Lot of people are telling me its the same but with a different crank and pistons. How is this? I have a 400 in my truck and i love it. But the same people say its gutless. I havent had any problems with mine at all. So if there is a website or if there is someone who can tell me the difference between the two would help me out a lot cause im confused. Thanks in advance. Also what does the "M" stand for like 400m or 351m?

 

When the 351 Cleveland was withdrawn after the end of the 1974 model year, Ford needed another engine in the 351 cubic inch (5.8 L) class, since production of the 351 Windsor was not sufficient and the 390 FE was being retired as well. To replace the 390, Ford took the 400 engine's tall-deck block and de-stroked it with the shorter throw crankshaft from the 351 Windsor, and taller pistons, to produce a 351 cubic inch (5.8 L) engine whose components were largely compatible with the 400. This engine was called the 351M and as a back-formation the taller-deck block became known as the M-block.

The M designation is commonly referred to “Modified”, and is derived from the use of both "Cleveland" (block, heads) and "Windsor" (crankshaft) components in the same engine, a modification for the parts' intended application, so to speak.

Another origin of the M designation may have come from where the engine blocks were cast. It follows the naming convention set forth by the 351C (Cleveland) cast at the Cleveland Foundry and 351W (Windsor) where the majority of the blocks were cast at the Windsor Casting Plant. From the introduction in the model year 1975, the 351M engine blocks (which are the same as the 400 engine block) were all produced at the Michigan Casting Center (MCC) in Flat Rock, MI or at the Cleveland Foundry (CF) also known as the Cleveland Casting Plant (CCP). To help distinguish it from the other two different 351s, the logical choice was to use the Michigan Casting Center, hence the “M” designation for 351 Michigan.

The 351 Cleveland had a well known, good reputation in the public. For a few of years after the introduction of the 351M, Ford marketing called the engine the "351 Cleveland". This led to confusion as to what 351 version was actually in the vehicle.

Later, car enthusiasts incorrectly referred to this engine as a "351 Midland" presumably a reference to Midland, Michigan, a city just northwest of Saginaw or reference to an iron foundry in Midland, Texas. But the Ford Motor Company never owned a “Midland” factory.

Engine dimensions are as follows:

Nominal main bearing size: 351M/400 = 3.000 in (76.2 mm) 351C = 2.750 in (69.8 mm)

Rod length; 351M/400 = 6.58 in (167.1 mm) 351C = 5.78 in (146.8 mm)

Deck height: 351M/400 = 10.297 in (261.5 mm) 351C = 9.206 in (233.8 mm

 

Oh wow that helps out a lot!! So then my 400 in my truck is basically a 351m right? The truck came stock with a 351w and the previous owner pulled it out and rebuilt a 79 400 and put it in there. I knew the guy that did the work he didn't want to sell it but he was moving. Also what rpm should my shift point be? Its a manual truck i shift right at 2500 was wondering what my power band shift would be? Thanks in advance

 

No. If you do in fact have a 400 cid, your engine has a crank stroke of 4.00" to gain 50 cid over the 351M's crank stroke of 3.50".

400 cid.
Bellhousing pattern same as 429/460 (to allow use of already existing heavy-duty transmissions.
Main journal diameter increased by 0.25" to 3.00" for greater bearing surface area (incidentally, same as a 351W)
Crank stroke increased from 3.50" to 4.00" to gain 50 cid.
Deck height increased from 9.206" to 10.297" accommodate larger stroke
New intake manifold for wider deck.
Heads are identical in design to 351-2V, but have larger chambers to reduce compression, may also have air injection ports.
Different harmonic balancer and flexplate than 351C

351M
Same block as 400, but crank is back to 3.50" stroke.
Pistons have thicker compression height to maintain compression a 8.2:1 in the tall deck.
Different harmonic balancer than 400

 

Oh ok i got ya thanks for the info it helps me out alot!!

 

The truck came stock with a 351w and the previous owner pulled will be out to rebuilt 79 400 and put it in there. The truck is manual works very strong then previous one to develop this kind of works .