'64 Dart GT: 273 for 318 poly ?

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my7tb

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According to the research I've done, the '64 273 shares the 318 poly crank, and possibly other parts, designs, etc. from it. I'm wondering then, could the 273 in a '64 Dart GT 4-speed be swapped with with a 318 poly ('65 truck) ? Any issues with motor mounts, clearances, etc. ? Custom headers needed ? Any other snags / concerns ?
 
You don't want a 318 Poly in your early-A.. They are both larger and a lot heavier than a smallblock.
When they developed the LA engine (273-360) for use in the compacts they were based on components from the Poly but with weight and size in mind.
The 318 Poly is a 50's design, nice engine but likes gas and is by no means a performance engine.
 
On second thought, instead of me trying to explain in a foreign language, here's a cut and paste on the subject :wink: :

The A engine was produced from 1955 through 1966. 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.
Bill Watson noted that the 273 carried over the A engines’ crankshaft, bearings, bearing caps, vibration damper, and timing chain, and conecting rods (if you want to interchange them, though, you need a 273; the 318 and other engines used different rods.). The LA bore was smaller, though the stroke was the same, and camshafts could not be shared.
 
I don't know whether I agree with that assessment or not, although I DO agree that I see no good reason to stick a poly into an A just because you have one.

If you were to tear a poly and an LA down to the short blocks, you would have a VERY difficult time telling the two apart. In fact, the heads "nearly" interchange.

The real practical difference between a poly and an LA is the heads and intake.

I keep hearing people call these a "wide block" because of the large heads. The fact is that the blocks themselves are about the same.

Weight? I'd bet there is not as much difference as you might think

This guy claims to have actually weighed the important parts which changed:

http://www.moparchat.com/forums/showthread.php?t=117690

A partial quote:

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The LA (lightweight 'A' engine, lest we forget... ) only differs from the Poly in any significant manner in the heads and block. Crank, rods, timing cover etc are the same or interchangeable, while many other things (rockers, pushrods, cam) would be so close to the same weight as to be the same weight.

So I really only had to weigh a block and a head. Out with the bathroom scales!

Results:

Poly 318 block with main caps,
cam bearings in place,
main shells in place, original bore (3.91") .......... 192 lbs

LA 318 block with main caps,
cam bearings in place,
most main shells in place, original bore (3.91") ... 168 lbs

Poly 318 head with valves and springs only ........ 51 lbs

LA 318 head with valves and springs only .......... 48 lbs

Sum total difference is somewhere in the vicinity of 30 lbs.

Though this is ignoring another area where the LA might be lighter... the manifold. I really should weigh them. I know the Poly manifold comes in at 53 lbs, I can imagine the LA manifold is lighter
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The Poly's cave eats, or possible cave eats for this idea are as followed.

The crank, at the rear, may have an issue in the register for accepting a newer converter or 4 spd. I'm real bad in this area, sorry, but some of the old cranks are not set up to take a new part. They can be machined to do so.

Headers are an issue. While TTI makes headers for a Poly, they may not fit at all since there designed for a B body. There are no A body designed TTI headers.

Performance items are out there and the 3 biggest concerns are,;

1, Intakes. They are hard to come by and often VERY expensive with the last E-bat 4bbl. Weiand single plane intake I seen sell go for over $600. Dual quads fetch more, complete set up's are amazingly rare with price tags going over $1500 with ease.

2. Camshafts. Racer Brown is the only guy that will have any camshaft on hand for you for this engine. Comp Cams, Crane, etc... (Any Major cam house/grinder) will custom make one for you if you know what your talking about.)
Cam prices are reasonable.

3. Pistons are only made by Egge machine and come only in cast with limited compression ratio's. OR you can have them custom machined by any maker for about $1,000.

Otherwise, the heads are the short coming in term of there ability to flow air. They can move a decent amount, but, do not flow like mad. If you plan on a powerful build, this must be taken into account for the plan.

For the most part, the "A" engine will accept most performance "LA" parts.
And I do believe they will have no issue in the use of engine mounts as well.
 
67Dart273 is correct. I had taken a Poly apart. The term "Wide Block" comes from the intake manifold giving the appearance of the block being wider. The head/intake look at this attaching point is different than a "LA" and very noticeable.

The head interchange he mentions is absolutely correct. I have tried it in my garage. Itis almost possible. The area of concern is where the water jackets are to cool the head and intake. It could be possible to weld your problem away. However, at the cost of doing so, it would be crazy to pay.

Give me a minute or so to post pictures that I need to resize.
 
Thanks Rocket. I understand the weight concern, and that being the reason why the 273 was made with a thin-wall casting. I'm looking for a performance upgrade for my car though, and have a 318 poly sitting in the garage. I know the polys of the 50's didn't have a lot of power, but they didn't have much for compression ratios, etc. either. The 318 polys can be stroked (Mopar Performance crank) and bored to 402. I've read articles that mention that they're actually underrated torque monsters. I'd be willing to beef up the car for such a swap if needed. But, would the 4-speed and engine compartment accept it ? Or, would it still be better (due to the extra weight of the poly, etc.) to stay with a small-block and somehow make a 360 work with the trans ?
 
1st shot, "LA" intake up top a Poly

2ND and 3rd, passenger and drivers side shots of the"LA" up top the Poly.

it fits all around, it would seal.
 

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Yes, use a modern 318 or 360 for much better results.

Water outlet in the center of the intake ports from the Poly block is a huge issue and probably something that will not be able to be overcome.

Then the 2 block shots, Poly then LA. and a comparo (Intake side) head shot.
 

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Thanks, Rumble, but I wasn't suggesting anyone do a top end conversion. Years ago, we sold a shortblock to someone with ???? forgotten, but it was near the changeover year, and the customer, it turns out, did not know which he had. We ordered, and sold, whichever short block was wrong. He actually got part of it together before "things didn't go well." I had no idea, until, later, we got both shortblocks sitting together in the back room.

This of course was before (long before) Al Gore invented the internet.
 
I didn't see it as you suggesting anything. Funny story though. Ehhh, crap happens.
 
Try this one on for size: strip the poly down to a bare block, drop a 4 inch crank into it, bore it out to 4 inches, use 360 pistons, have a 402, use cleaned up Magnum heads, early 5 bolt valve covers, tell every one you hot rodded your 273. It would be a killer, and 99.2% would never know the difference.

This is just the result of a random neuron fireing.
 
4spdcuda66 said:
The poly will be a difficult fit in an early A, mostly because of exhaust manifold clearance. Custom headers would no doubt need to be fabricated and probably would only fit with manual steering. As far as performance goes, Jim Richardson can give some advice there. http://www.moparmecca.com/ Here is an old article from Mopar Muscle on poly 318 performance. http://www.moparmusclemagazine.com/..._give_a_318_poly_engine_more_power/index.html
Click to expand...

Interesting article. But I would have to say if he took a LA 318 block and stroked it he would come out cheaper and have the same amount of torque and hp (if not more) for the same amount of money.
 
True dat Cliff. I posted the article to illustrate the potential of the mighty poly 318 since he said he already has one lying around. In the poly's defense, they are really good running reliable engines. I have one in my '67 Fury. Fresh rebuild about 25,000 miles ago and very reliable.
 

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4spdcuda66 said:
True dat Cliff. I posted the article to illustrate the potential of the mighty poly 318 since he said he already has one lying around. In the poly's defense, they are really good running reliable engines. I have one in my '67 Fury. Fresh rebuild about 20,000 miles ago and very reliable.
Click to expand...

Did you do stock rebuild or do one like in the article?
 
Valiant Rebel said:
Did you do stock rebuild or do one like in the article?
Click to expand...
Stock rebuild with .040 oversized pistons to clean up bore taper. Really good running engine. Nothing to write home about HP wise but it pulls that Fury down the road with no trouble and close to 20 mpg.
 

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That's a 67 correct? I thought they had LA 318, My Dads 67 did.
 
Don't let other people dictate what YOU want to do with YOUR car. The 318 ploy engine is a formadible power plant. Go here, and READ.

http://www.1962to1965mopar.ornocar.com/poly318.html

Lots of good info and some links there. There's even a part number by part number list for a stroker poly. I say if you wanna do it, go for it. Yeah, it's a wide *** motor and you might have to move some stuff around and do some fab work to get it in, but you'll have something different. Read the web site and follow the links for more info if you like...but whatever you do, don't let someone else tell what you don't want. Make your own decision.
 
Valiant Rebel said:
That's a 67 correct? I thought they had LA 318, My Dads 67 did.
Click to expand...
Some '67's had the poly and some had the LA. I checked the engine code digit on the vin and fender tag with the "white book" and both confirmed the poly engine. In the 1967 service manual there are USA built and Canadian built engines. The poly is the Canadian engine the manual refers to. 1967 was the last year for the poly, although it is commonly thought to be '66.
 
No performance parts for a poly? Yeah, right.
 

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The only problem with that picture is that the intake is a custom built T-ram. You can have that done for any engine. All it takes is cash.
 
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