Re: Beginners question sorry

[Gary Pavlovich <glpavlovich@xxxxxxx>]

Dave,

The  318A "Poly" engine that many refer to is nicknamed a "Poly" because the 
head design is a Polyspherical combustion chamber with canted valves (angled 
intake & offset from the exhaust - not in the same plane and side by side as 
the Wedge chamber) as opposed to a HEMIspherical chamber.
The Plymouth Poly was produced from 1956-66 as a 277, 301, 303, 313, 318, 
and 326 (1959 Dodge only) and shares many of the same parts as the later 
273/318/340/360LA Wedge-head engines.  Sometimes the aforementioned 
Wedge-head engines are mistakenly called "A" engines which can be confusing.
Interestingly, the modern 4.7 Chrysler engines are a Polyspherical chamber 
design and not a wedge design; even the new HEMI's are not true 90degree 
Hemispherical valve layout.
The BMEP, brake-mean-effective-pressure of a Poly engine is far superior to 
the Wedge chamber and slightly behind the HEMI;
"...the poly engine had one absolutely unique feature: its volumetric 
efficiency. If the Mopar figures as found in the Plymouth factory manual are 
to be believed, torque of the poly 318 was 345 lb.ft. Now, take torque and 
divide it by cubes, then multiply this by 151, and you get brake mean 
effective pressure (bmep). Try it for your self: bmep for the poly 318 is 
164 psi. (Again, that's the figure Plymouth gives). That is near to the 
theoretical limit for an unsupercharged engine (and that's with the old 
log-type exhaust manifolds too) and is very close to the 426 hemi's bmep of 
173psi, which had all those performance-designed components. The bmep figure 
purely reflects breathing efficiency (proportional use of the charge coming 
into the engine), and is a product of the head, as opposed to the block, 
which just needs to suck/blow as rapidly as possible without flying into 
little pieces..."
Gary Pavlovich
----- Original Message ----- 
From: "Dave Isle" <mnwildpunk@xxxxxxxxx>
To: <1962to1965mopars@xxxxxxxxxx>
Sent: Thursday, December 10, 2009 8:56 PM
Subject: Beginners question sorry


> I see a lot of you guys saying you have a poly this or a poly that. I know 
> it is a type of engine but which one is it and what makes it a poly.
>                Thank you for being patient and answering this probably 
> silly question.     Dave
> Sent via BlackBerry by AT&T
>
>
> ----
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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!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html.