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Old 06-24-2007, 09:49 PM   #1 (permalink)
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What are the differences between the 351C and 351M and 400 engines? And, what are the differences between the 351C and 351M blocks specifically?

Thanks in advance.

Jay
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Old 06-24-2007, 11:44 PM   #2 (permalink)
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I did some research on this when I recently bought my '73 and concluded that the 351C is more desirable. The 351M is identical to the 400M except that the 351M has been destroked. The M's are some of the first generation motors with emission controls and were produced at the end of the 351C production. The M's were generally low compression motors and were ubiquitous through the '70s and part of the 80's. If you thought 1973 was a bad year for the 351C in terms of emissions, low compression, and HP loss, well the 351M/400M were even worse.

I did find a 351M/400M diehard who swears by them and has tips on coaxing out the beast within.

As far as specifics, some info can be found here:
http://reviews.ebay.com/351W-351C-35...AT:-1:SEARCH:3
http://reviews.ebay.com/Ford-351-Cle...00000001410755
http://home.earthlink.net/~bubbaf250/index.html
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Old 06-24-2007, 11:48 PM   #3 (permalink)
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Rereading your post, you had specific questions and I rambled on without really answering them. Here they are:

Quote:
the 400 or incorrectly 400m 2V only, produced from 71-82 is similar to the 351c, but uses a taller block,wider intake,bigger main bearings. they share 2V heads,cams,valve covers,oil pans,front covers,distributors, which are basically 351c, the 400 has 429,460 bellhousing bolt pattern and specific engine mounts , best identified by intake valley width, 351c Valley width measures 6-31/32", 400 measures 8-17/32"

the 351m (75-82) 2v only is basically identical to the 400 as it is a simply destroked 400 using 351c,351w bore & stroke. not easily identified,looks just like a 400,came mostly in trucks, but the 400 was an option in trucks also. easiest to identify by measuring the stroke, 351m is 3.5 & 400 is 4.0, cut & paste the links below to veiw casting numbers for cranks,etc.
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Old 06-25-2007, 02:18 AM   #4 (permalink)
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The 351c, 351m, and 400 engines are all part of the 335 series engine family. What distinguishes the 351m/400 blocks from the 351c is they have 1.1" taller decks and the 429/460 bellhousing bolt pattern as previously mentioned. 351m and 400 engines are built on the same blocks. The main bearing size on the taller deck blocks is 3" vs 2.75" in the 351c blocks.
You'll probably never see a 351m or 400 in a Mustang.
1) they were never factory installed, the 351c was the only 335 series engine offered in the Mustang
2)in spite of some part interchangability with the 351c, the m and 400 never gained much acceptance as a performance engine and had very limited aftermarket support so there wasn't any real motivation to swap it into a Mustang
3)the 351m and 400 used motor mounts unique to those 2 engines so they are not a simple bolt in swap. Combine that with the need to swap the trans for a big block unit and the cost to benefit ratio for swapping this motor isn't very good.
I won't say it's never been done, just that they were never factory intalled and since they weren't popular or easy swap candidates it's very unlikely you'll ever see one in a stang.
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Old 06-25-2007, 09:53 AM   #5 (permalink)
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The 351M/400 is much wider than a 351C. Good luck finding exhaust manifolds/headers that will work with the shock towers. The stock 351C exhaust manifolds will NOT work with a 351M/400.
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Old 06-26-2007, 10:36 PM   #6 (permalink)
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The 400M is a very good engine. The problem is that it came out after they changed the calculations for HP in 1972. It has a taller deck than a 351C (which is desireable), and more degrees between the cylinders (left bank vs. right bank) which is also desireable. You can make a 400M into a big block eater pretty easily. It is significantly less weight than a big block as well.

Rickmaan is right though, not much support in the aftermarket world which is a shame. The 400M is a great engine that got saddled by the gas crunch.
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Old 06-27-2007, 08:23 PM   #7 (permalink)
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[quote=Cruise] It has a taller deck than a 351C (which is desireable), and more degrees between the cylinders (left bank vs. right bank) which is also desireable.

Huh? Do you mean it's 94*V? It's almost as wide as a 460 with almost no aftermarket support. Some came with smallblock bellhousing patterns.
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Old 06-27-2007, 10:24 PM   #8 (permalink)
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Oops! I was a little tired when I responded. Degrees should have been inches. Wider!

The 400M is 145 lbs. lighter than a 429/460. Has 3" main bearing journals, 10.297" deck height, and 6.58" rods - which is the longest stroke of any Ford pushrod V8.

The real issue is to get the compression ratio up. You have to shave the heads and use a 9:1 piston.

Note of warning though: Don't bore it past .040" as they have a thinner wall. Also, you need to make sure you are not using a block cast at Ford's Michigan foundry prior to 3/2/77 as they had water jacket cracking problems.

Finding aftermarket parts is really a myth. Granted, there aren't as many as other engines, but they still make aftermarket parts.
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Old 06-27-2007, 10:39 PM   #9 (permalink)
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A 1970 351 C , w/ closed chamber is the best of the 335 family isn't it ?
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Old 06-27-2007, 11:02 PM   #10 (permalink)
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Quote:
Originally Posted by Apprentice

A 1970 351 C , w/ closed chamber is the best of the 335 family isn't it ?

More desireable - yes. Best? Depends on what you want. The 351C revs faster than a 400M, but the 400M has better lower end torque.

If it is going in a Mustang, then stick with a 351C as it will look more correct.
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Old 06-28-2007, 01:04 AM   #11 (permalink)
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That would only matter if their was a 20 foot race in existance, but last I checked after 20 ft everything is behind me including you and you're motor :p
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Old 06-28-2007, 01:17 AM   #12 (permalink)
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There is no such thing as a 400M. Ford only ever made 1 engine designated as a 400 so there was no need to assign a letter to differentiate it from other engines like they did with the 351W, 351C, and 351M.
It can be argued that the timing of it's introduction in the market kept it from being developed into a performance engine, with emmission regs mandating low compression and retarded timing just 1 model year after its appearance. However, it only existed because the marketing dept determined it would be beneficial to sales if they had a 400 ci option available for luxury sized cars, particularly since GM and Chrysler already had 400's on their option sheets. Internal memos from Ford indicated they never intended to use it as a performance engine or in anything other than large cars and some trucks. In order to make it to production in the shortest time possible Ford chose to alter an existing engine design as needed to accomodate 400 ci rather than build an all new design from scratch. The 351C was a natural starting point to make a 400 since the heads (even the 2v) flowed well enough as is, so they just stretched the block to fit a longer stroke and beefed up the mains to handle the added mass and stress of a 4" stroke pulling around a 4000lb car.
To get back to the question, does all of this make the 400 (or its brother the 351M) the best 335 series engine? Not really. While it is a subjective question that really has no concrete answer, I'll go out on a limb and say that if your goal is to have the most HP in an engine package that will easily bolt into a Mustang or similar sized Ford/Merc car, any of the closed chamber 4V 351C would be a better choice than either the 400 or 351M, followed by all the other 351c varieties. The 400 can be made to perform reasonably well, if you swap to closed chamber C heads to get decent compression and use spacers to fit a 351C intake, then fabricate some headers to fit, and fabricate mounts to put it in your car, etc. etc.
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Old 06-28-2007, 01:53 AM   #13 (permalink)
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Well said, very articulated answer with allot facts, also need to point out that the NASCAR racing teams of the 70's knew which one of these 335 class motors ruled... that would be the... [color:red]1970 351 C w/ CLOSED CHAMBER HEADS !![/color]

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Old 06-28-2007, 09:22 AM   #14 (permalink)
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You want power from a Cleveland? Stroke to 408.

As I stated before, you are NOT going to get a 400 to fit in a 65-70 Mustang without a really special set of headers (which would suck because of the sharp turn coming out of the heads) or notching the shock towers.
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Old 06-28-2007, 10:20 AM   #15 (permalink)
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Quote:
Originally Posted by Apprentice
That would only matter if their was a 20 foot race in existance, but last I checked after 20 ft everything is behind me including you and you're motor :p
.....apparently your 8th-grade spelling classes are far behind you as well.
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