M-Block 351M/400 History

Copyright © 1999-2003 by Dave Resch
All rights reserved.


From 1977 to 1982, the M-block (351M/400) V8 engine was a mainstay of Ford light truck powerplants. During that period, the M-block 400 was the largest engine available in any Ford 4x4 truck. In the 1978 and 1979 model years, the 351M and 400 were the only engines offered in Ford’s new, full-size Bronco.

The following sections provide some background on the M-block engine’s origin and design.

Ancient History
The 400 was introduced in 1971 as a longer-stroke variant of the 351 Cleveland, and it would be the last pushrod V8 engine ever designed by the Ford Motor Company.

 
The 335 Engine Family
There were two engine types in the 335 series engine family, the 351 Cleveland (351C) and the “M-block.” There were several minor variants of the 351C engine (including the basic 2V and several high-performance 4V versions), but there were only two M-block variants — the 351M and the 400.

 
Demise of the M-Block
The ultimate cruel irony in the M-block’s history was that it was so well adapted to first-generation emission control systems, it was not easily updated to work with more modern engine management systems, and it was dropped from production at the end of the 1982 model year.

 
Big-Block Comparisons
An M-block engine in factory trim has vast, untapped power potential. It is smaller and lighter than a 385-series big block (which is why it was developed in the first place), and when properly built, the M-block 400’s output is comparable to most big blocks.

 
M-Block Availability
M-block engines were used in most of Ford’s mid-size to full-size cars and station wagons from 1971 to 1979, as well as in pickup trucks and Broncos from 1977 to 1982.

 

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