The performance difference mainly is the strength. The rotating assemblies can be made very close to equal as they share rods and crank, and the race 440 pistons are almost as light as the street 451 pistons. The 400's bore helps with shrouding, but take the 440 to +.060 and they are the same bore size. The 400 is about 40lbs lighter IIRC. The main webbing is a bit stronger. Even 450hp 440s will eventually suffer from either cap walk, or the main webbing failure. It's just a matter of how long until the inevitable happens. But as the hp levels drop to the 450 range, you really need to beat on them to have them come apart. I had one that had over 550 passes and 6 years of street duty. But it exploded at 3K rpm and ruined everything but one head. In terms of A bodies and head choices, the 451 could be much more cash if you have raised exh ports like the Victors or Indy heads. Because the headers are expensive. In terms of realistic performance ina street car, they are the same thing. least that's how I look at it. If this was a bracket car, I'd say use the 451 build. Street car, not much difference, use what ever is cheaper.
