I haved owned cars and trucks with both 351M and 400. I have always liked the engines. I have a good 351m in the garage now on an engine stand that I hope to build before summer. I will be going with the 400 crank and pistons. My question is Why would ford have made both a 351M and a 400. Is there any application where the 351 would be preferable over the 400. My build with the added expense just has me wondering

 

It was my understanding that the 351M came about the time emissions and milleage were really getting strict so they nocked 50 cubes of the 400 that had already been in production for a few years. Also if I am not mistaken the 351C was being phased out and they needed another powerplant to fill in. The 351m also went into alot of cars wich had more strict emissions and more of a demand for fuel economy as compared to most 400's that went into heavy duty trucks.

 

You can read more about the 351M and 400 (no M) in the tech papers here:
High Performance Options for the 351M/400 Engine by Dave Resch

 

Here's my latest speculation on the rationale for the 351M:

https://www.ford-trucks.com/forums/s...d.php?t=305136