Dartswinger70
Well-Known Member
I read somewehre that someone was glad to see an LA under the hood when they came out. What was better about the LA vs the Poly it replaced? I seem the think the HP on the Poly was 230,and the LA 318 was 235 etc.
Poly Engine what was good/bad about it and why is the LA better?
- Thread starter Dartswinger70
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Primarily, LA was lighter (LA = "light A") and cheaper. Bore and stroke for both was the same. I'm guessing not much if any difference in head flow. Rated hp for both was 230.
I wouldn't be too concerned about rated horsepower. That got fudged too much back in the day, up or down.
I wouldn't be too concerned about rated horsepower. That got fudged too much back in the day, up or down.
Professor Fate
Push the button, Max...
Really, it was all about size and manufacturing costs. The LA was lighter due to the newer thin wall castings and the wedge heads made them dimensionally smaller, to fit more easily in cars a like the A bodies (the poly was an "A", "LA"s were "Light A"s if I'm not mistaken...). The poly heads (which were actually quite good for their day) cost more to produce than the LA variety, kind of like the situation with the Hemi vs. wedge BB heads.
Chrysler needed a V8 to put in their small cars, and assembly line installation of a poly into an A just wasn't practical- so they went with the LA and dropped the poly.
Chrysler needed a V8 to put in their small cars, and assembly line installation of a poly into an A just wasn't practical- so they went with the LA and dropped the poly.
There was a four barrel version of the poly 318 available 59 through 62. Had 260 hp. Besides the four barrel carb and dual exhaust, it also had a mildly hotter cam, with 248 degrees duration vs. the 240 of the 318 poly two barrel. That 248 degrees of duration, coincidentally, is that same as the later 273 four barrel.
Professor Fate
Push the button, Max...
There was a dual-quad version, too; if I remember correctly...
The 318 poly is the reason early 273's had an alternator bracket with four head mounting holes. Two are for the poly 318, two are for the 273. Both motors used the same bracket. Many other parts same, too, including timing cover, pulleys, crank and rods.
Oh yeah, 57 and 58 Furies, which had a 256 duration cam and dual four barrels. 290 hp.
Also, there was an optional dealer-installed dual quad intake and hot cam for the 303 poly in 56 Furies, which gave it 270 hp - up from the standard Fury's 240. Standard Fury 303 had a single four barrel; same cam duration (around 240 degrees) as the 277 poly four barrel (200 hp), but with tighter lobe separation, which gave it a few more horsepower (as did the extra 26 cubes and higher compression ratio). Can't remember the duration of the optional Fury cam.
Scamp Rhonda
Well-Known Member
All of the above is Really good information! I knew none of this before. Thanks much.
MopaR&D
Nerd Member
The Poly chamber and valve arrangement was marginally better for combustion efficiency and flow compared to conventional wedge heads but that was easily made up for by increasing the compression ratio. According to my "Chrysler Engines: 1922-1998" book by Willem Weertman the LA was a revision on the A-engine to reduce weight and width so they could offer a small V8 for the new (at the time) A-body cars. Somebody on here once tried to argue that the "L" did NOT stand for Lightweight but in this book written by the head engine engineer at Chrysler at the time that's exactly how he describes it, "Lightweight A". I believe they were able to shave 50 lbs off the A-engine while still keeping the heads and intake manifold cast iron.
Also because of the wedge head they were able to take advantage of quench/squish and run higher compression ratios, at least on the early LA engines with closed-chamber heads. My big question is why they dropped closed-chamber heads for LA engines after 1967(?) and never bothered trying them again until the 1985 318 roller-cam engine. Literally since the beginning of Chrysler Corp they were pioneers in making flathead engines with "high-turbulence combustion chambers" which was a quench pad. They knew its benefits back in the 1920s so why toss it out? Unfortunately it's not mentioned in the book in the chapters about our beloved V8s...
Also because of the wedge head they were able to take advantage of quench/squish and run higher compression ratios, at least on the early LA engines with closed-chamber heads. My big question is why they dropped closed-chamber heads for LA engines after 1967(?) and never bothered trying them again until the 1985 318 roller-cam engine. Literally since the beginning of Chrysler Corp they were pioneers in making flathead engines with "high-turbulence combustion chambers" which was a quench pad. They knew its benefits back in the 1920s so why toss it out? Unfortunately it's not mentioned in the book in the chapters about our beloved V8s...
The LA was better for Chrysler, because it cost less in production. The poly engines arguably have better potential in their heads. They just never really caught on. The LA was smaller, lighter and cost much less for Chrysler to make. The cars were getting smaller and less and less room was available for such a wide engine. While the blocks are identical in terms of shape and size, the heads made the 318A engine much wider and with all of the little A bodies in the early and mid 60s, Chrysler needed something different, so the LA was born. The polysphere engine had a great run though, all through the 50s all the way to 66. They were great engines, all of them. Dodge, Chrysler, Plymouth and Desoto all made their own versions of polys for many years. They wouldn't have wasted time on a POS design.
By the way, the 1956 dealer installed dual quad intake and hot cam could also be installed in a 277, which upped the hp from 200 to 230.
And while I'm discussing arcane and mostly useless info about a motor family that hasn't been produced for well over 50 years, one more thing I only learned recently:
If you get a timing cover gasket set for a small block, you'll notice that there is one extra water pump gasket that doesn't fit whatever small block - A or LA - you might have. Turns out that the 56 motor has a different timing cover, that places the water pump higher on the motor than 57 and later. In other words, the 56 water pump and timing cover are unique to that year. Reason being that the 57's were lowered several inches from 56, and so the radiator was lower to clear the hood, so the water pump had to be lowered too. And the 57 water pump was also re-designed. So the water pump gasket changed.
I only found this out recently when I put a new timing chain in my 56. Its timing cover is cast iron, and I was thinking I might change to a later aluminum timing cover. But no - that would have lowered the water pump, which would have lowered the fan to where it wouldn't be in the right place for the radiator. So, I finally found out what the extra water pump gasket is that's in every small block timing kit I've ever bought.
I kept the 56 timing cover and water pump, but I did swap in a 65 poly 318 crank damper (the 56 didn't come with one) and pulley, and bolted a 273 timing tab to the bottom of the water pump. That tab clears the damper by probably an inch. Still usable, but it doesn't hug the damper like it does on a later A/LA.
And while I'm discussing arcane and mostly useless info about a motor family that hasn't been produced for well over 50 years, one more thing I only learned recently:
If you get a timing cover gasket set for a small block, you'll notice that there is one extra water pump gasket that doesn't fit whatever small block - A or LA - you might have. Turns out that the 56 motor has a different timing cover, that places the water pump higher on the motor than 57 and later. In other words, the 56 water pump and timing cover are unique to that year. Reason being that the 57's were lowered several inches from 56, and so the radiator was lower to clear the hood, so the water pump had to be lowered too. And the 57 water pump was also re-designed. So the water pump gasket changed.
I only found this out recently when I put a new timing chain in my 56. Its timing cover is cast iron, and I was thinking I might change to a later aluminum timing cover. But no - that would have lowered the water pump, which would have lowered the fan to where it wouldn't be in the right place for the radiator. So, I finally found out what the extra water pump gasket is that's in every small block timing kit I've ever bought.
I kept the 56 timing cover and water pump, but I did swap in a 65 poly 318 crank damper (the 56 didn't come with one) and pulley, and bolted a 273 timing tab to the bottom of the water pump. That tab clears the damper by probably an inch. Still usable, but it doesn't hug the damper like it does on a later A/LA.
One more thing I forgot to mention. Early 273 timing covers had one extra bolt boss about halfway up the driver's side. That's because the 318 poly had a bolt there. 273 didn't, but used the 318 poly timing cover as is. So it still had provision for the bolt that a 273 didn't use. Eventually, LA timing covers were updated to eliminate the unused bolt hole, but I don't remember when that happened.
Very cool! Can we have some more pictures?
pishta
I know I'm right....
Soo...a hotter 248 (273/4ish) cam in a higher compression 68 318 LA with a 4bbl could potentially crank out 260HP? Touche.....
Professor Fate
Push the button, Max...
The cam specs may have been the same between the 248 and 273, but the cams can't be interchanged between A and LA. The port layouts are different, therefore the cam lobes are sequenced differently. Same core, different lobe layout.
I've posted a few pix of the car here and there on this site. Be happy to post more. What do you want to see?
BTW, I bought the 56 Plymouth at Mopars at Big Daddy's twenty years ago. Doesn't seem possible I've had it that long.
The engine man! lol
Keith Mopar
Mopar Nut
Another cool thing is the electronic LA distributer can drop right in on the Polly engines.
The duration was the same. I haven't been able to come up with lift figures for the poly 318 four barrel. 273, of course, is .415/.425. Very mild cam, actually.
I've heard people say the 273 hi-po had a "hot solid lifter cam." But it wasn't much hotter than the two barrel cam, which was also a solid lifter cam - same as every A motor ever built except the 59 Dodge 325 (or 326) poly, which was just a .040 over 318. Dodge was still exclusively a mid-priced car in 59, so had to have a bigger motor than the Plymouth. Besides the extra eight cubes, the Dodge poly also got hydraulic lifters. Next year, Chrysler Corp said the heck with this and dropped the 326 poly; was 318 from then on.
And, talk about hp ratings, the extra eight cubic inches of the 59 Dodge motor somehow bumped the power up to 255 - still with a two barrel carb, single exhaust and the same compression ratio as the 318 poly. Twenty five hp from eight cubic inches. Pretty good trick. . . .
Professor Fate
Push the button, Max...
If you want engines, Rusty? Here you go-
I posted these in another thread the other day when I was in a "Poly" kind of mood...
67Dart273
Well-Known Member
All I know is, in the early 70's, stationed at NAS Miramar, and my street driven pretty-much-my-only transporttion 70 440-6RR would run low 13's with 3.54 gear. A guy "I used to know" showed up in a stock class 63? B body with a Poly and big 2bbl and ripped off 13.0's. I don't remember what class they built it for, he claimed "it was right on" the national record, and THIS was the first runs with the car
If you search around the video might still be up.......someone at engine masters built a poly. I think they actually used an LA block?? I've forgotten the particulars
This is not the engine I was thinking of BUT
Daniel Boshears Brings a Poly 318 Stroker to the 2018 Engine Masters Challenge
Another one
If you search around the video might still be up.......someone at engine masters built a poly. I think they actually used an LA block?? I've forgotten the particulars
This is not the engine I was thinking of BUT
Daniel Boshears Brings a Poly 318 Stroker to the 2018 Engine Masters Challenge
Another one
Here's a couple. When my generator crapped out the third time (once was my fault), there was no longer anyone in Tallahassee who could rebuild a generator, so I converted to GM one wire alternator. Then someone on ebay offered a new chrome one he had bought for a street rod and then sold the rod. Starting bid was $60 (Speedway's price was $150), so that's what I bid. No one else bid, so I got it and swapped the natural finish alternator for a chrome one.
Distributor is a Mallory Unilite for a small block Mopar - which fits all A motors, too. Carb is a 500 Edelbrock. I used a die grinder to open up the throttle bores in the factory four barrel intake. I still have the original WCFB and huge oil bath air cleaner, so I could go back to stock, I suppose.
Except for the carb, distributor and glass packs, it is completely stock. Supposed to have 200 horsepower, actual net power is probably less than 150.
I also have an old Edelbrock P600 three-deuce intake, but the carbs would cost me probably $1000 and wouldn't make any more power than the setup I have. The cool look of the three two barrels is not worth the cost to me. At least not yet.
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The Poly heads were a cool design. The valve train had to be different to make it work. Similar to the Hemi in many ways.
The head bolts hold down the rocker stands.
The head bolts hold down the rocker stands.
yes, I had one of the manifolds years ago, 290 hp.
I has been said that is the the engine in Christine {demon car} is a 290 hp dual quad poly, watch the movie closley it is a 4 bolt valve cover BB (probably a 350 , i believe first year for BB was 58. there were some b engines that had factory dual quads. The only one I can think of now is the 383 343 hp, with dual carter AFB
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