What is the best of the 3? I know that is probably like asking what the best beer is but lets see what opinions are out there.

I found a 351M for sale and the guy is trying to tell me it's a big block.

Am I wrong or are not all the 351's small blocks?

 

Well, big and small blocks are really terms that are better at confusing than anything else. Ford has what they call engine families. You can scroll down the list of forums on this website and see which displacement engines belong to which family.
Having said that, the 351M from all that I understand is actually a 400 with a different stroke which lessens the displacement. Hence the crankshaft is different.
Which of the three 351 engines are the best? Yes that is exactly like asking which beer is best, and you can talk for days on this subject and never get anywhere really. I think they are all great engines because they are Ford engines myself. Some folks talk bad about the 351M but thats what mine has in it and it's been one of the best engines if ever used, hands down. Only reason id like to change to something different is fuel economy, as any old v8 is not great in that area. So first, you have to decide what it is you want from an engine and then research which ones have that.
someone else will chime in on this who is prolly a lot more knowledgable on this than myself.

For example: The 351M, 351C, and 400 belong to the 335 Engine Family
The 351W belongs to a different engine Family

Heres a pretty good list: Ford Classics - Engine Specs
However im not so sure about some of the statements describing the engines. May or may not be accurate

 

A 351M is a big block and as Justin said, it is the same block as the 400M with a different crank/stroke. When I rebuilt my 351M in my 78 I bought a 400 crank and made my 351M a 400M. Also a 351M is a "modified" 351C, which is also a big block. Some smarter people can explain what the modifications were on the 351M as compared to the 351C, I am not sure. But I can tell you I loved my 400M engine, it did have some 72 Cleveland heads on it though, but it was a great motor for me. Tough as nails and it was bored 60 over with no problems. Loved that truck and unfortunately had to sell it 10 years ago
A 351W is a small block and that is what I am using in my 76 F100, currently under construction. I have ran both engines and I personally could not say one is "better" than the other. I would take either one. I have never had a 351C...

 

Call it what you like but the 351m-400 is not a big block it just shares the 429-460 bellhousing pattern.

 

As said, Ford=engine family, not big or small block. But commonly used anyway, and so I will explain a bit.

Any Windsor or 335 series (that includes 351C, 351M, and 400) would be considered small blocks. Their dimensions are the same at the block area, thus the 351M or 400 can drop right into the engine's frame perches of a 302 truck, and vice versa. Take a '78 Bronco, and you can drop a 351W right in without any frame mods. The difference between them is deck height. With deck height, you get wider intakes. With wider intakes, you get more surface area for bellhousing bolt patterns. The wider bellousing bolt pattern makes for a larger flywheel or flexplate which means more turning mass for more torque. The 351M and 400 do share the 460's bell pattern.

That being said, depending what your engine is now, you might have to change transmissions depending on your current bell pattern and engine.

Personally, I would go with the 351W based on performance parts availability. But I like the 335 series engines for shear brute force. I would take a 351M and make it a 400, so just a 351M is out. My two cents.

 

Like boss said, call it what you will... There are differing opinions on the Cleveland blocks (including the modified.) They have always been big blocks to me but I am certainly no authority on the matter and I guess it really doesn't matter what you call it... I am sure a 460 is a big block and a 302 is a small block
If you do a google on it there are lots of opinions both ways big bock or small block. Interesting link here, but proves nothing:
Answers.com - What is the difference between a big block engine and a small block engine

Justin was right all along these terms just confuse people LOL

 

Confusing, it can be, yep. Here's something else for reference:

 

Thanks havi! Good info!

 

I'd like to try a stroker 351w, 393ci, then put some 351c heads. 393clevor! I know its possible, just never heard of any one run one.

 

351W hands down is the "best" due to availability of parts and cost.

351C would be best for power, due to the better head design, but would be more expensive to build than the W.

The 351M, a destroked 400, needs to be made into a 400 again to have a prayer of decent power.

As for BB/SB:

If you accept BB as deck height of 10", you would call the 351m/400 a BB. But it has SB cylinder spacing.

The C has a shorter deck than the W, so you can call those two SB if you like.

351CJ and Boss motors made great power in the day:

https://www.ford-trucks.com/forums/9...omparison.html

Run from the 351m, unless you have a boat in need of an anchor.

 

Well I'd be interested to hear how many you've run... The 400 is a tire pounder. I've had a stock 400, a built 351W, and a built 400, and with a *touch* of the gas, the stock 400 would wake up and push like niether of the other two could.

That said, to answer the original question, the 351W can be set up to be a racer for less money than the 351C, but if you're comparing stock engines (if you don't plan to do major work to whichever you choose), then I would go with the 351C.

AleX

 

OP asks about a 351m, not a 400. Stock, the 351m is hopeless.

 

As someone else pointed out recently, there is no "400M" its a 400, a 351M is a destroked 400, hence the "M".

Ford motors can be confusing cant they? I remember 25 years ago we had farm trucks we had bought from uhaul and other places, some, we never were quite sure what motor they had in them lol. Is it a 330 a 360 or a 361, 390, 391?? We didnt know about FT motors or FE families. Does this pickup have a 351C, W or an M and what the hell is the difference?? This was before the internet. A machinist told me and Im not sure wether to believe him or not but he said Uhaul had a special fleet engine and you couldnt get parts for it, sounds like BS but who knows. IH trucks were almost as mystifying.

 

The 351/400M's now have Edelbrock heads that can make them real contendors on the street.

351C heads are only good in you have the closed chamber 4V design originally. Or you have added the 2V closed chamber from down under. Other then that they are the same as 351/400M's in just about every respect except deck height.

351W are probily the best if it a no money concerns here build. Large aftermarket and the ability to cheaply go above the 400ci mark.

As far as budget 351W is a bit cheaper here too, 351/400M for cheap "storkers", but this can still depend on which one you have or source cheapest.

 

Perhpaps I'm being a bit simplistic, but the 351C is great as a higher revving powerful engine, but that somewhat contradicts the purpose of a truck, which is typically in need of good grunt at the low end. The 351C and the 351W are not typically known for low rpm torque (not that they can't produce it later on in the power band, but I'm specifying the low end for a reason...."truck" use). As I've read in a number of articles, the secret of torque production in a 335 class engine is a 2v head configuration. You wouldn't clamp down a good breathing 351C with 2v heads, as that would be contradictory to where the engine shines, so I'd not favor the 351C for truck use (in this very narrow focus).

The 351W is also a very good engine, and has a huge after market, but again, it still usually shows it's power a little higher in the rpm band, which doesn't necessarily suggest an inherent ability for low rpm grunt.

The 351M, as others have suggested, is merely a 400 with a growth or glandular disorder. It's not to say it doesn't have any potential....quite the opposite. To put it in a completely confusing way....the 351M is a 351C that has been given growth hormones (taller deck = 400), but then hit on the head with a hammer to dumb it down (destroked). That being said, the 351M is going to be butt cheap to get, as there are bunches of them out there, and nobody thinks they're worth anything. So, I'd say get the 351M, bring it back to 400 specs with the 400 kit from TMeyer (crank and a set of flat top pistons), change the silly retarded timing set from the factory to straight up, and you'll have an engine that will produce grunt at the low end.....which is what a truck should have (again....hugely narrow focus here....I know trucks can have any number of uses).

Regardless of your choice, any of the three can be made into a good engine, but it's all about your needs, and the inherent characteristics of the engine. I'd say that for low end grunt, the 351M can be made to produce it easier by just making it a 400 and addressing a couple minor factory retardation issues (timing, oil pressure, reduced CR).....for high rpm power, the 351C can be made to produce it easier as it was capable of high revving power in the first place with the 4v heads....and for midrange power, the 351W probably can fit the bill as easily as the 351C, but can do it more cheaply due to the availability of the aftermarket parts. The 351M could also be made to make good midrange power, but you'd have to make up for it's shortcomings by making it a 400 anyway, and then make up for shortcomings on the higher rpm band (oil pressure, timing, etc....= $$$).

Granted, I'm waaaaaaaaaay oversimplifying this, but the original question was so loaded that there's no easy way to just answer it outright.