Re: Mopar terms pt 1 'Poly'

[Herb <zephyr9900@xxxxxxxxxxx>]

>From Ancient Greek prefix ἡμι- (hēmi-), “‘half’”) < ἥμισυς (hēmisus),
“‘half’”)  Chrysler became identified primarily by trade marking the "Hemi"
name and then using it extensively in their advertising campaigns beginning
in the 1960s. Chrysler has produced three generations of such engines: the
first (the Chrysler FirePower engine) in the 1950s, the econd (the 426 Hemi)
 developed for NASCAR in 1964 and produced through the early 1970s, and
finally the "new HEMI" in the early 2000s. The "Hemi" engine introduced in
2002 by DaimlerChrysler had a combustion chamber featuring valve and twin
spark plug locations markedly different from the second generation 426ci
version. The current-production "Hemi" V8 with its pinched chamber, does not
have true hemispherical combustion chambers despite the name; rather, it
bears a closer resemblance to the mid-1950s Polyspherical chamber, which
Chrysler engineers developed as a lower-cost alternative head for their V8
engines. The Polyspherical head needed less metal and was narrower due to
using only one rocker shaft. This saved costs in material, space and
warranty claims and allowed it to be used in smaller vehicles.  With the
hemispherical combustion chamber design, the intake and exhaust valves are
usually on opposite sides of the chamber, allowing for the combustion
mixture to flow directly across the chamber, commonly referred to as 
cross-flow" heads.

The Chrysler A engine is a small-block engine from Chrysler Corporation. It
was produced from 1956 until 1967, when it was replaced by the wedge-head LA
engine. The A engine's combustion chambers are polyspherical, and it is not
related to Chrysler's Hemi engine of the same era.  The hemispherical head
and complex valve operation added to the cost, size, and weight, and
lengthened build time. To address some of these issues, the company adapted
the Hemi engines by substituting more polyspherical-shaped heads, with
valves activated by a single rocker shaft. Not quite a full hemisphere, it
still had a rounded, circular combustion chamber that could be served by a
single rocker arm. To manage this, they put the valves in a diagonal
arrangement, with intake valves on the top side of the rocker arm and the
exhaust valves on the bottom side. The bottom of the new engine's valve
covers were uniquely scalloped so the spark plugs were accessible from the
top.  Another advantage of the poly engines was better low-to-mid-speed
performance, for ordinary drivers of sedans and wagons.  The LA, introduced
in 1964, had the same basic design but was very heavily modified. The
lightweight ("L" A) or thin-wall casting and heads saved around 50 pounds;
the wedge-shaped combustion chamber was much smaller than the A engines’
poly heads, greatly reducing the size and allowing the first LA engine (273
V8) to fit into the small Valiant. The LA's valves were simpler too, saving
money and size. The 273 ended up being only fifty pounds heavier than the
225-cid slant six.



          
 Herb 
 
1956 Plymouth Belvedere 361
1959 Coronet 326 Poly
1963 Fury 2D/HT 6.1
1963 Sport Fury Convertible 361
1970 Challenger RT 440 - 4 Sale
1999 Durango SLT 5.9
2008 SRT-8 Magnum 6.1
St. Louis, MO.
 
http://1962to1965mopar.ornocar.com/mmo42009.html
  
 
 
 
-------Original Message-------

From: David Bailey
Date: 03/11/10 05:15:37
To: 1962to1965mopars@xxxxxxxxxx
Subject: Mopar terms pt 1 'Poly'
 
 
 
As I mentioned in a previous note, I’m new to this group and to Mopar
products in general. I also gave fair warning that I would have a lot of
Mopar questions. So, as a warm-up, I’d like to begin with some silly dumb
questions that have been plaguing me for some time yet everyone else seems
to fully understand. Lets start with “terms”. For instance – ‘Poly’? She
seems quite popular in the Mopar community. I hear of poly 318 ci motors and
even poly paint colors? Are there non-poly 318 motors? What does ‘Poly’
refer to?
Dave B
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Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html. 

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