351M Ideas

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I've seen this question a few times. Just for grins I'll toss this out. The original 400m was used in 70 or 71 ltd cars, not trucks. The importance to to the discussion is that year only, those blocks had sbf bolt pattern for the bell housing. It might be impossible to find one of those rare blocks, but there out there. The only parts that are custom only would be forged pistons, beefy rods or forged cranks. With all the long rods on the market, custom pistons, ( need them made any way ) and some custom crank grinding?? All the rest, heads, cams, distributors are cleveland stuff.
Is it worth doing. Other than getting very lite side loads on the pistons. No. If you have room to use this block go with a 460. Much cheaper parts and still way cool. Even better be really unusual and use an LS3. Great milage, tons of power and lots of " WTF" when you pop the hood.
 
I've seen this question a few times. Just for grins I'll toss this out. The original 400m was used in 70 or 71 ltd cars, not trucks. The importance to to the discussion is that year only, those blocks had sbf bolt pattern for the bell housing. It might be impossible to find one of those rare blocks, but there out there. The only parts that are custom only would be forged pistons, beefy rods or forged cranks. With all the long rods on the market, custom pistons, ( need them made any way ) and some custom crank grinding?? All the rest, heads, cams, distributors are cleveland stuff.
Is it worth doing. Other than getting very lite side loads on the pistons. No. If you have room to use this block go with a 460. Much cheaper parts and still way cool. Even better be really unusual and use an LS3. Great milage, tons of power and lots of " WTF" when you pop the hood.


You know, I've replaced 400M's in '71 LTD's that came with them from the factory, and none of those engines had smallblock bolt patterns--they all had the same standard 351M/400/429/460 bolt pattern . . .
 
The 400's with the SBF bellpattern were installed in something like a 72 Stationwagon. First year for the 400 was 71. These were the only "high compression" (with a 9 to 1 ratio) 400's. There was also a 4 bbl version that year, which were even rarer than the small block bell pattern blocks. In any case then only classic Stangs these things will bolt into are the 71-73 cars.
 
You guys are really bashing the M block. I think no one on this board has ever seen or heard of one of these that has been done right. The M block is actually a fantastic platform and it is very easy to make power with. Headwork, the right cam and a good intake and it will haul ass. These blocks can make TONS of power. The main issue is the lack of aftermarket support. The M block is actually a very good design for a street car as its always going to make a boat load of torque. Put a good 4 speed behind one with the proper cam profile and you will toast a small block all day long.

That being said, its a biyatch to fit these in the smaller Mustangs. If I had a chance to build an M motor and had a good chasis to put it in, I'd do it and I'd suprise the crap out of all of you guys.
 
I just built one up for my 77 F-150 4X4. After 363,000 miles it was getting a little tired. My truck has the NP465 4 spd. we have been talking about also. I am a huge fan of cleveland engines. I have no regrets that I built one. I would have gone with the 460 for the extra cubes, but the only one company I found for the conversion parts wanted big bucks. I wanted to keep the 4 spd and not be relying on one source for parts. A Weiand 4bl intake, Edelbrock truck carb and cam, Headman elite coated headers, 70 mustang 2v heads for bit higher compression over M heads. I do have to worry about breaking u-joints and axles now. And I do get 14-15 mpg in town. Was getting 11 mpg just before the tear down.
I think most people never tried one with a 4v carb. Keep your foot out it and helps mpg alot. Stomp down and will easily bust the tires loose. I think most stock 70's trucks with 350-400 ci engines were lucky to see 12mpg. No I see people bad mouth this engine and just smile, cause I know better.
 
You guys are really bashing the M block. I think no one on this board has ever seen or heard of one of these that has been done right. The M block is actually a fantastic platform and it is very easy to make power with. Headwork, the right cam and a good intake and it will haul ass. These blocks can make TONS of power. The main issue is the lack of aftermarket support. The M block is actually a very good design for a street car as its always going to make a boat load of torque. Put a good 4 speed behind one with the proper cam profile and you will toast a small block all day long.

That being said, its a biyatch to fit these in the smaller Mustangs. If I had a chance to build an M motor and had a good chasis to put it in, I'd do it and I'd suprise the crap out of all of you guys.


As everybody mentioned, it's a very big (external dimensions) engine; it's also very heavy--probably within a few pounds of a 429/460 . . . if you're going to go with an engine that big (externally) and weighs as much as that one does, to me it really doesn't make any sense to build anything other than a 429/460 at that point.

My preference is big cubes . . . as someone once said: "There is no replacement for displacement", and I don't care *what* all the little ricer boi's say! LOL!

:D
 
You know, I've replaced 400M's in '71 LTD's that came with them from the factory, and none of those engines had smallblock bolt patterns--they all had the same standard 351M/400/429/460 bolt pattern . . .



you sure they were 71's and not later models? because he's right the first year or two the 400 was available in passenger cars it did have a small block bolt pattern.

there were also "big block" FMX trannies as well, back to the c6 argument here, that were used behind the early (but not the earliest) 400 motors that used a special bellhousing which is almost as rare as the early SBF bolt pattern 400
 
As everybody mentioned, it's a very big (external dimensions) engine; it's also very heavy--probably within a few pounds of a 429/460 . . . if you're going to go with an engine that big (externally) and weighs as much as that one does, to me it really doesn't make any sense to build anything other than a 429/460 at that point.

My preference is big cubes . . . as someone once said: "There is no replacement for displacement", and I don't care *what* all the little ricer boi's say! LOL!

:D

I agree, much more after market support, and 60 extra cubes to start with. Bottom line is it would be very hard to get either in a 65.
 
Hey I wasn't knocking on the 400m, I just said it would be a better choice to go with something else in a Mustang because the of cost to get the motor to fit into the car. If they are built right they are a pretty good motor. :nice:
 
You guys are really bashing the M block. I think no one on this board has ever seen or heard of one of these that has been done right. The M block is actually a fantastic platform and it is very easy to make power with. Headwork, the right cam and a good intake and it will haul ass. These blocks can make TONS of power. The main issue is the lack of aftermarket support. The M block is actually a very good design for a street car as its always going to make a boat load of torque. Put a good 4 speed behind one with the proper cam profile and you will toast a small block all day long.

That being said, its a biyatch to fit these in the smaller Mustangs. If I had a chance to build an M motor and had a good chasis to put it in, I'd do it and I'd suprise the crap out of all of you guys.

The biggest hurdle with these engines is the lack of off the shelf pistons that bring the piston top up to the deck at TDC. All the stock replacements leave it .100-.125" down the bore. That means, no matter what head you choose, the pistons are too far down the hole to give any kind of quench. So, you're looking at a set of slugs that're going to set you back $500 or better. I've built a 400, using a set of 351C forged flat tops & ported and milled 351C 2 bbl heads. What I ended up with was a motor with 9.7 to 1 compression that wouldn't run on anything less than 93 octane premium. I had a higher compression 390 (10.25 to 1) that would run on 89. The 400 cost me $2000+ to build. That 390 was less than $500.
 
The lastest issue of Popular Hot Rodding magazine has the results of the Jegs Engine Masters challenge, and guess what engine won? You got it, a 400 M, built by Jon Kaase. There were several other 400 M engines in the competition, all making BIG HP.
I do agree that this is NOT an engine for a 65 - 70 Stang, but for anything that will hold it, it will not dissapoint. It is quite a nice looking engine also when done up right.
David.
 
you sure they were 71's and not later models? because he's right the first year or two the 400 was available in passenger cars it did have a small block bolt pattern.

there were also "big block" FMX trannies as well, back to the c6 argument here, that were used behind the early (but not the earliest) 400 motors that used a special bellhousing which is almost as rare as the early SBF bolt pattern 400


Yep, I'm sure it was '71 LTD's and one in particular I can remember clearly, had a broken crank; we replaced that engine with a 351M (this was about '77)

I started working on cars when I bought my first car in '75 (a '64 Fairlane 500 2-dr Sedan with a 289 2-V and a C4), and in a year and a half, I was working in a shop part time; around February of '77, I started working in the shop full time, so it was some time after that.

In all that time, I have *NEVER* seen a 400 block that had a smallblock bolt pattern . . . I'd really like to see one, if you can scrounge up a pic!

That would be interesting!
 
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78 F250 would have a Granny gear 4 speed. Basically a 3 speed with a deep reduction 1st gear. It's not a performance transmission.

Borg-Warner T-18, 6.32:1 1st gear, 7.44:1 reverse. With a typical 4.10 rear gear you can put it in reverse, let the clutch out at an idle, get out and walk around the truck and get back in, all before its moved 20'. Not the ideal performance trans.

As for the M not making any power, try telling that to Jon Kaase. Having said that, I still wouldnt touch one, especially to put in a 66. Just get a Mustang, Mark VII or Explorer 5.0L and be done with it.
 
Yep, I'm sure it was '71 LTD's and one in particular I can remember clearly, had a broken crank; we replaced that engine with a 351M (this was about '77)

I started working on cars when I bought my first car in '75 (a '64 Fairlane 500 2-dr Sedan with a 289 2-V and a C4), and in a year and a half, I was working in a shop part time; around February of '77, I started working in the shop full time, so it was some time after that.

In all that time, I have *NEVER* seen a 400 block that had a smallblock bolt pattern . . . I'd really like to see one, if you can scrounge up a pic!

That would be interesting!

I spent a little time scrounging the library. It was in the '73 ltd with fmx trans. I was thinking of the one time they had a 4v carb. It is mentioned in " how to rebuild Ford engines V8" by Tom Monroe. They had no pics of the block that I saw.
 
I spent a little time scrounging the library. It was in the '73 ltd with fmx trans. I was thinking of the one time they had a 4v carb. It is mentioned in " how to rebuild Ford engines V8" by Tom Monroe. They had no pics of the block that I saw.

Heh heh - - I also have never seen a 400 with a 4-V carb, either! I think I have that book laying around at home somewhere . . . I'll see if I can dig it up and the reference to it you mentioned.

I know there isn't anything listed in the Encyclopedia of American Cars regarding a 400 with a 4-V carb for any of the years up through 1975 . . . if there is such an animal (either a 400M that came with a smallblock bolt pattern, or one that came with a 4-V carb), I'd sure like to see it!

:D