400 or 351 - how do I tell?

A 400 is a 400 is a 400. The only "Modified" that ever existed was the 351M. It was just a letter to diffrentiate it from the 351 Cleavland and the 351 Windsor. The 351M is a 400 block and heads with a destroked crank and different pistons. They never changed the motor mount boss in the block.

So... what is a 351M400?

BTW 351c not only got c4's and FMX's but they also got c6's

Originally Posted by dbu8554

BTW 351c not only got c4's and FMX's but they also got c6's

And 4 speed top loaders

Originally Posted by canoe

So... what is a 351M400?

THIS HAS BEEN MY QUESTION FOR YEARS IS IT A 351 OR A 400? i THINK IT MEANS A 400 MODIFIED TO A 351. I know insurance companys and Gas prices of all thing(LOL) forced auto makers to detune things but why create another 351 when you had a 351 windsor?

They are genrally lumped together because they are identical in every way except the crank and the pistons. The 400 debued in 71 and the 351M came along in 75. No idea why they felt they needed another 351 cubic inch motor after they killed the cleavland, they just made one. If anything its the 351M thats the mystery not the 400.

the reason for the 351m was simple:

using the high deck 400 block meant the same transfer line for machining...kinda a two-for-one production plan- the 351 was well known, realistically theres probably a lot of folks that didnt know the cleveland and windsor were vastly different...ford got to sell their 'well known' 351 and still offer a bigger version for free...thats how Ive heard it anyway.
the problem with the 351m is the piston/rods are too heavy to be 'ideal' (had to be taller to meet the 400 deck height). the bad thing about the 400 was it was 2bbl only- but the 4" stroke was one of the biggest around so it still made a boatload of torque for moving a boatload of fullsize car around...