Why did Ford make the 351M?
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Senior User
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From: British Columbia
Why did Ford make the 351M?
Hi, quick question. The 351M as far as I know is a 400 block and rods with a 351 W crank and special fits-one-engine-only taller pistons. Why did Ford make this engine, especially when the 351W and 351C were available-351C only to 73 but they must have still had the molds. I know the 351W and 351C were "small block" bell housings and the 351M was the same as the 385 series. Anyway, could they not just use the 400?. It would seem to me that if you had the same carb, intake, valves and bore (351M and 400) the fuel mileage should be the same? could they not produce enough 400's?. Was it to compete with the 350 GM trucks but with a tougher (C6) trans versus the C4? I've always wondered why. Any input welcome.
P.S although I find the 351M gutless until it is given a 4BBL and headers to take advantage of the 351C heads it is still a very reliable engine and will go forever.
007BRONCO
P.S although I find the 351M gutless until it is given a 4BBL and headers to take advantage of the 351C heads it is still a very reliable engine and will go forever.
007BRONCO
Laughing Gas
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From: Yuba City, Ca
ok the 400 is based off the 351M block. the only difference was the crank and pistons. on the 351M the bore and stroke was 4.00x3.50 whereas the 400 was 4.00x4.00 inches. The reason the 351M was created was because FORD had to meet emission standards in 1977. They brought out the 400 to give a more powerful option to the V8 and still keep the emissions within standards. Sometimes the 351M is reffered as the "Smog Motor." I believe the reason for the 2-BBL was to keep decent fuel millage. I hope i explained this good enough. it's lated i'm tired and gotta meet a deadline by 8:00 tomorrow for work. If anything isn't clear tell me and i'll try and clear it up. lol 
If You Ain't Good In The Saddle Lord She Won't Be Satisfied!!!
If You Ain't Good In The Saddle Lord She Won't Be Satisfied!!!
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If you are looking at supplying 2-5 million units of an engine and you can do it by using the exact same block, heads and accessories that your bigger engine uses, with only tuning changes and changes for the missing 1/2" stroke. Then you could save millions of dollars by using existing assembly lines and parts. Then you can have your epa/mpg covered and save money too. You don't have to expand existing plants or try to re-tool old ones to build discontinued engines. Although I think they could have done much better by using Chevy's idea of one bellhousing for either and two basic engine families, they didn't. But hind-sight is 20/20 too.
Posting Legend
Joined: Sep 2001
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Actually the 351M is based off the 400 block not the other way around. The 351M does not use the 351W crank. Ford needed more 351 sized engines than the existing plants could supply so they downsized the 400 design to produce the destroked 351M version off that assy line and tooling.
The bellhousing bolt pattern was designed to house a larger clutch or torque converter. The larger clutch/TC was needed to transmit the torque that the 400 produced.
You can read more here:
The bellhousing bolt pattern was designed to house a larger clutch or torque converter. The larger clutch/TC was needed to transmit the torque that the 400 produced.
You can read more here:
MSEE
Joined: Apr 2004
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From: Austin, TX
Wasn't the 400 created just before the EPA cracked down? Seems like the '71 400's were pretty powerful from the factory, and later on they started loading them up with smog equipment. I think by the time the 351M came about, the 400 was deemed a smog motor?
Laughing Gas
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torque 1st is right from what i read years ago.ford wanted to dump the cleveland which they did in 74.the windsor plant couldnt keep up with demand for 351s.by using the 400 block the saved the cost of a seperate block.
Postmaster
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From: wi
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From: British Columbia
torque 1st, The main and rod journal sizes of the M and W crank are identical-obviously so is the stroke, and I'm sure I read somewhere (think it was a Ford performance book that it was the windsor crank dropped in the 400 block with 400 rods connected to tall pistons,created the 351M.) That would be using another existing part right. Why tool up to make a new crank for a stop-gap engine?. You are probably right and I'll never know until I find that damn book......
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007BRONCO
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007BRONCO
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The 71 400's are pretty stout, even with a two barrel. Mine has no smog junk and I get 20-21 mpg on the highway. Btw, 007Bronco, I have the Ford book that says the cranks are the same. If you need something from it let me know. Ford's reasoning for the 351M is the Windsor plant couldn't keep up with the demand for an engine with that displacement since the 351C was dropped. I think that the conecting rods were also something the was unique the the 351M to go with the pistons.
Posting Legend
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They just rounded that one up to 352 to make a different name. The rest just used a letter. Figure out the displacement for the 300-6 and the 302. Then figure out why one is a 4.9L and the other one is a 5.0L... -Marketing, some numbers seem to sound better???
The 71 400 is my favorite engine. Unfortunately that is the only good year for the 400.
The 71 400 is my favorite engine. Unfortunately that is the only good year for the 400.