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Old 08-10-2008, 08:58 PM
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318 Poly Engine

G'day guys,

1. What is a Poly engine & how do you identify one externally?

2. What is the difference between a Poly engine & the 318 V8 that was fitted to the Australian made Valiants etc.?

I have just bought a 318 & 904 auto trans that came out of a 1968 Dodge Charger & I would like to know what this engine is. It was the original engine from the car.

I have been told that the Poly engine is the better engine of the two & that it has a different combustion chamber shape. That's all I know.

Growing old is unavoidable,
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Old 08-10-2008, 09:15 PM
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I can tell you that Chrysler did not manufacture the Poly head engine in 1968. The last year of manufacture for the poly head was 1967.

You can tell a poly by checking out the pictures in this thread. They were made with a couple different valve cover designs but both are pretty much the same internally. The poly, although a good design and ahead of its time was pretty much left out of the "performance" race. Finding performance parts now days is a challenge.

If you Charger was a 68 it should have an LA 318. When it comes to a 318 you want an LA engine which is the same design as the 340 and 360 and has much more performance potential.

Last edited by Centerline; 08-10-2008 at 09:21 PM.
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Old 08-11-2008, 08:23 PM
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Re 318 Poly Engine question

Thanks centerline,

My engine is an LA 318.

Cheers...........John
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Old 08-11-2008, 08:40 PM
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they make Torque
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Old 08-12-2008, 07:13 AM
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318 Poly was the base engine for 1966 and 1967 Chargers
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Old 08-12-2008, 12:31 PM
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The 318" Polyspherical engine was big, hell-for-stout and reasonably good performer. It was based upon one of the first-generation-smaller-hemi block - maybe the DeSoto. There are next-to-no performance parts for it. IIRRC, Rod&Custom or one of the other off-brand rodder mags did a major feature on the Poly a couple of months ago - lots of good info in it.

thnx, jack vines
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Old 08-12-2008, 03:18 PM
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Quote:
Originally Posted by Packard V8
The 318" Polyspherical engine was big, hell-for-stout and reasonably good performer. It was based upon one of the first-generation-smaller-hemi block - maybe the DeSoto. There are next-to-no performance parts for it. IIRRC, Rod&Custom or one of the other off-brand rodder mags did a major feature on the Poly a couple of months ago - lots of good info in it.

thnx, jack vines
Hot Rod did a build years ago ,,was pretty strong
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Old 05-02-2009, 09:48 AM
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Quote:
Originally Posted by rough_idle
G'day guys,

1. What is a Poly engine & how do you identify one externally?

2. What is the difference between a Poly engine & the 318 V8 that was fitted to the Australian made Valiants etc.?

I have just bought a 318 & 904 auto trans that came out of a 1968 Dodge Charger & I would like to know what this engine is. It was the original engine from the car.

I have been told that the Poly engine is the better engine of the two & that it has a different combustion chamber shape. That's all I know.
The Poly head engine was a derivative of the early Hemi engine, based on the Dodge Red Ram 241CI engine. It was produced in the 318 in size 1957 to 1966 when the 318 LA engine was produced. Your Charger has the later model 318 LA 2 bl engine that was the standard V-8 in the 68 Dodges. It is the same engine family that includes the 340 and 360 engines. As for which is a better engine, well it depends on who you talk to. I like both of them, but the performance parts are a lot more plentiful for the LA engines. The Poly which you can identify easily by the 2 bolt scalloped valve covers are a heavier casting. They can be safely bored .090" to open the bores to 4.0 and the poly head, which is a canted valve head has a lot of flow potential. If I was in your shoes, I'd work with the LA engine you have. Another question, is this an Aussie Charger, or a Charger from the US? The engines will be the same, but the body is a lot different.
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Old 05-02-2009, 11:52 AM
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Ya, getting hi po parts for the poly isn't real easy but if you know where to go, it's not all that bad but being from down under, your cost is going to bite. These people here http://www.diamondbackengines.com/ know poly engines pretty good and the owner, Damon, really knows his stuff. They are heavily into Nostalgia Super Stock racing but they are into a lot of other things too. Their machine shop does excellent work too which is kinda rare around here in the Houston area if you are a Mopar freak. Houston is very much a Chevy town.
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Old 05-02-2009, 04:13 PM
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I'd heard that the Houston area had a good MOPAR support?? I know Dallas does, but you have to find them. The same old story, Chevy owners will always outnumber us 5 to 1. That's why I love to see a MOPAR win in any style racing. I remember back in the 70s when NHRA refactored the Super Stockers to the point it was extremely difficult to compete. I was running a Stocker and a S Stocker back then. The Stocker was a 70 Charger RT. I had about every engine/trans combo available from the factory in it trying to fill a slot. I would do real well with the std 440, then refactored. I switch to the 6-pack, refactored. I ran a Hemi in B/S until I was refactored. I finally ran in G/S with a 383 and all the R/t badges removed. Super Stock was just as bad. I started with a 71 Cuda and went all up and down in combos. Best overall successs was with the 440-6 in it. I still have the Charger. It was caught up in a shop fire a year or so ago and I haven't taken the time to restore it. I'll try and post a photo. If I can figure this forum out. LOL


Speaking of Poly heads, I had an old 58 Fury that had the 2X4 setup. Now that was a fun old car. Some of my favs from that era are those NASCAR specials that were always slipping through. My mom owned a Chry-Plym-Dodge dealership and our bodyman has a NASCAR Pontiac. Man we use to have a blast with those cars. Wish I'd kept a few, but can't cry... "well not to loud," over spilt milt.
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Old 05-02-2009, 04:19 PM
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Well finally figured it out, so here is a sad sight. Luckily its cosmetic damage, the drivetrain and suspension wasn't hurt.

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Old 05-02-2009, 04:29 PM
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Since you're in Australia, I have a good buddy that lives in Trott Park S.A. has a 68 Charger R/T that he has restored. Here is photo of him with it last year. I've been trying to figure out how to get one of your Hemi 6 Charger's over here to the states. I love oddball engines and that 6 is a legend with the MOPAR community here in the States. Of course you also have those wonderful Sport Ute's.

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Old 05-07-2009, 02:21 AM
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Quote:
Originally Posted by badsam56
The Poly head engine was a derivative of the early Hemi engine, based on the Dodge Red Ram 241CI engine. It was produced in the 318 in size 1957 to 1966 when the 318 LA engine was produced. Your Charger has the later model 318 LA 2 bl engine that was the standard V-8 in the 68 Dodges. It is the same engine family that includes the 340 and 360 engines. As for which is a better engine, well it depends on who you talk to. I like both of them, but the performance parts are a lot more plentiful for the LA engines. The Poly which you can identify easily by the 2 bolt scalloped valve covers are a heavier casting. They can be safely bored .090" to open the bores to 4.0 and the poly head, which is a canted valve head has a lot of flow potential. If I was in your shoes, I'd work with the LA engine you have. Another question, is this an Aussie Charger, or a Charger from the US? The engines will be the same, but the body is a lot different.
Thanks badsam, The LA 318 I bought was from a Charger imported from the USA. It is being fitted to a 1934 Plymouth 4 door sedan Hot Rod that I am currently building.
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Old 05-07-2009, 04:27 PM
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Now that is way too cool. I use to have a 37 Plymouth 4 door sedan with a 340 in it. It was a great cruiser and those suicide doors are neat. I'm also glad you're keeping it all MOPAR. The 318 is good platform for a hot rod. It's easy to modify and it will respond well to simple bolt ons.
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Old 10-29-2009, 03:17 PM
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Simplest way of telling the Poly 318 is the bolts through the top of the rocker covers...

Up to '61 there were three of them, after that they dropped the centre one out. They aren't based on any of the old Hemis at all.

Earlier there were Polys that were based on Hemis, but in those the heads interchanged as the blocks were identical for both Hemi and Poly versions. The scalloping of the rocker covers was much more pronounced in those engines.

The 318 Poly engine's bottom end is pretty much identical to the LA. Just a bit of wasting of some weight here and there in the LA so it could be the 'Lightweight A' engine, while the Poly was the 'A' engine.
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