Well, some things that come to mind are size and
weight. A 318 poly weighs about almost as much as a big block and takes up a
comparable amount of space. Chrysler had to develop the 273 to have a V-8 that
fit in the A-bodies (nevermind that within a couple years, they had figured
out how to make a 383 fit).
Also, dies wear out, and in the long run its
probably cheaper to replace stamping dies for the LA valve covers than for the
poly. Also, don't forget that they're not that different. Cranks, rods,
distributors, etc interchange, and the blocks are extremely
similar.
Its also cheaper to have two versions of the same
basic engine (chamber design and port orientation) so that if you design hi-po
manifolds for a 440, you can scale them down appropriately to work on a 340 with
similar performance increase. The same ideas go for pistons, cams, heads,
valvetrain, etc. Less R&D time costs less money.
Dave Casey
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