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Hemi to LA: How Chrysler went from the Hemi to their 1990s truck and Viper V8s
Feb 4, 2025
Evolution of the 1951 Hemi into the Poly, A, and then LA—which became the Magnum V6, V8, and V10 that lasted into the 21st Century!
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hi there this is Dave and I'm here to
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talk about how the Hemi became the LA
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small block V8 engine and it was kind of
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interesting because most people don't
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realize that the engine underneath the
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hood of a viper or a Dodge Ram from the
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1990s or even a late say Dodge Diplomat
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originated in the same Hemi that was
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known for the 392 racing cars so let's
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dive into it right now the engineers at
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Chrysler had been investigating numerous
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types of combustion Chambers for a brand
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new V8 which would be Chrysler's very
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first V8 engine they didn't call it the
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Hemi yet it had hemispherical heads but
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they called it the Dual rocker and
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that's actually what it would stay
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called until the days of the 426 Hemi
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which was in many ways completely
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unrelated so they started out with 331
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cubic in and it was a very powerful
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engine for the time and a pattern
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emerged where every time that they came
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out with a new Hemi the next year GM had
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an engine that beat it just on cubic
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inches keeping in mind for any given
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displacement it was really the ideal
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engine because the hemispherical head
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meant that you could have bigger valves
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it meant that you had more resistance to
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detonation it just provided more power
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and more efficiency but you could beat
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it by getting a big cheap wedge head
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engine and just making it bigger and it
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didn't take long for Chrysler to bump up
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against the maximum size of their engine
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which was 392 cubic in and the problem
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with the Hemi heads was that they were
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very expensive they were slow to make
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and they made the engine quite large on
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top and fairly heavy to make more V8s as
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it became clear that a V8 would not just
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be for Imperials and top Chryslers but
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that they would be needed by Dodge and
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doto and then even by Plymouth they
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switched to polyspherical heads which
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meant that they could cut out some of
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the valve gear and they could make the
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engines more rapidly and more deeply and
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without needing so much space in the
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engine bay the poly head engines were
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step one and are still called poly V8s
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because of their polyspherical heads and
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then you had the a engines and these
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were basically the poly engines with
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many changes made by the engineers so
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they could be built at new automated
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factories and then came the LA and that
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had even more changes it had a
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lightweight casting mostly and they
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switched to wedge heads as one engineer
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said they finally got rid of that silly
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polysphere because they tested the head
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designs again and they found that it
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didn't make a difference you didn't get
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extra power from the poly head as they
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thought that they would the wedge head
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allowed them to have more area for
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squish it was the better design and it
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was cheaper and they could make more
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engines faster which was great because
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Plymouth now needed a boatload of V8s
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and Plymouth was the volume brand no
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other brand at Chrysler was really mass
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mass production so over the years the LA
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engines were updated many times and they
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were improved many times and they were
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uh tuned for maximum performance with
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the famous 340 V8 and then they were
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tuned for maximum Conformity to
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emissions controls and they ended up
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with just two sizes the 318 and 360 or
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5.2 and 5.9 as they would eventually be
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known eventually they optimize those
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using computer models and then they
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optimize them again with fuel injection
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and then they optimize them again with a
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sophisticated sequential multiple port
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fuel injection system powering Dodge Ram
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pickups and such and of course we all
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know about when they took two cylinders
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off and made the 3.9 V6 and put those
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two cylinders back on again to make the
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Viper v10 I am of course simplifying and
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it was more than that but that's
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essentially where the Viper v10 came
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from it was the LA Engine with two more
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cylinders added on and that takes you w
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to the 21st century which is quite good
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for an engine which was at its heart the
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original 1951 Chrysler VA updated and
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modified and updated and modified again
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so you can see more much more detail
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about every one of these engine families
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and all the steps that they had to take
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with all the technical details at
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motels.com
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