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Poly 318

  
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Poly 318

 
Tim70Mustang Tim70Mustang
New User | Posts: 3 | Joined: 07/10
Posted: 07/26/10
08:11 PM

As long as you are on the subject what the heck is the difference between a regular 318 and a poly 318?

Poly is short for Polyspherical head. Some say it was a forerunner to the Hemi (Hemispherical head). Basically it was based on a theory that you could get more combustion or volume by angling the intake and exhaust valves then if you had them parallel. From Hemmings  Motor News book of Chrysler Performance Cars…”The ploy’s exhaust valve is located parallel to, but offset from, the cylinder axis.”  

This increased the efficiency.  The hemi was constructed to increase the efficiency with a more angled system. The shape that the valves make are semi-circular with the Poly being a little flatter than the Hemi.  I did the below image in Paint.
Image located:

http://timsweet.wordpress.com/2010/07/26/question-from-reader-dodgeplymouth-318-poly/  
Tim Sweet
Average Guy's Car Restoration, Mods and Racing
http://www.average-guys-car-restoration-mods-racing.com

skyeking skyeking
User | Posts: 243 | Joined: 11/09
Posted: 07/27/10
05:54 PM

Read the biography of Walter Chrysler and his team's creations
before and during WW2...  
skyeking

Rolling_Thunder Rolling_Thunder
New User | Posts: 48 | Joined: 04/07
Posted: 05/12/11
11:09 PM

The Poly engine is a weird beast...   had one in my 66 Plymouth Satellite...     it uses different heads (obviously) but the major component is the intake manifold...   no one makes an aftermarket intake anymore...    very rare to find a factory 4bbl, dual 4bbl, or aftermarket aluminum ones....    I've had two V800 intakes (iron dual quad) and one Weiand 4bbl...   bought the weiand for $40 and sold it for $790  

UNCLE_MIKE UNCLE_MIKE
New User | Posts: 2 | Joined: 12/11
Posted: 12/02/11
09:09 PM

one is a boat anchor for a 30 ft boat and the other is a boat anchor for a 40ft boat


seriously though the LA318 is good little motor. don't waste your time with a poly318 but why build one when you can build a 360 for the the same cost.  

pepsi1 pepsi1
Enthusiast | Posts: 301 | Joined: 10/11
Posted: 12/02/11
09:56 PM

Didn't know those things still get a mention today. Good riddens to the POLY 318. ALL boat anchors.  

Rolling_Thunder Rolling_Thunder
New User | Posts: 48 | Joined: 04/07
Posted: 02/26/12
11:00 AM

Well the 318 Poly was a good engine back in the day - the biggest problem is the lack of aftermarket support. The engines are good design in theory but never used as a real performance engine.  

Budnicks Budnicks
Enthusiast | Posts: 676 | Joined: 10/10
Posted: 02/26/12
04:42 PM

The 318 Poly-Spherical engine had it's purpose in Mopar's history it's considered the red headed ba$tard child of the Mopar engines, there are many still running very well still to this day, some people that have restored cars don't want, can't or shouldn't replace the engine, with the more modern 273-360 LA Small Block, there are very limited parts available for a high end performance application, they are out there but very expensive, but you can improve the power a whole lot, buy doing some intake exhaust & head porting & misc.head work, shaved/milled surfaces, larger valves, free flowing exhaust systems, hotter ignition conversions {within the original distributor}, custom ground camshafts {you can have your cam reground to a smaller base circle, to achieve more effective valve/cam lift & use custom push-rods or adjustable push rods}, higher compression custom pistons, offset ground stroker crankshaft {the limit is your imagination & time to source the parts & machine work}, carburetor mods, even a centrifugal supercharger with some custom mounts & pulleys, Weiand use to make a alum. 4bbl manifold, I think Eggy & PAW still sell some parts for the 318 & other Poly-Spherical engines, there are some parts occasionally on Craigslist & E-Bay you can't just open a catalog & order every part like you can with the, 318c1 LA or 5.2ltr. Magnum, but they are still very easily capable of 400+hp, if you do the proper things & you can still retain most of the stock appearances.. Good luck with your so called disrespected 318ci Poly "Boat Anchor", you should build it & prove every one wrong... Do a GOOGLE search there is NOS, new & used, stuff out there, the parts won't be cheap, "if there's a will there's a way", you will probably need to some custom parts & machine work or fabed parts, either way... The best of luck to you...  
"Fill Your Library Before You Fill Your Garage" Good Luck  "Budnicks"

Budnicks Budnicks
Enthusiast | Posts: 676 | Joined: 10/10
Posted: 02/26/12
04:48 PM

Try www.JalopyJournal.com Forum, also maybe www.62-65mopar.ornocar.com , as much as I hate to say it www.moparts.com main index, links & forum, www.dodgecharger.com forum , www.forbbodiesonly.com forums, there as a bunch of stuff, but mostly just information, available on some of those sites, there is a following just not as big as other engine platforms, stuff is out there you have to do some research & foot work.... Again best of luck...  
"Fill Your Library Before You Fill Your Garage" Good Luck  "Budnicks"