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Hemi to LA: How Chrysler went from the Hemi to their 1990s truck and Viper V8s
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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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