The difference between a 351M & a 400
Fleet Mechanic
Joined: Jan 2003
Posts: 1,812
Likes: 15
From: Central Ohio
The difference between a 351M & a 400
The only way I know to tell the difference is probably to get the motor tested for cylinder displacement. Not exactly sure how they do that but I have seen it done in racing were motors have to meet certain guidlines for class restrictions.
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
The difference between a 351M & a 400
You can try to measure the stroke through the spark plug hole but the best way to tell is to drop the oil pan and look at the casting numbers on the crank. 5M, 5MA or 5MAB is a 400 crank. 1K is a 351M crank. The casting code should be on the first crank throw.
