Plymouth, Dodge, Chrysler Poly A Block Engine Family 277 301 303 313 318 326 History and Myths

[@IndridCool54]

I’m an old dude and former automotive machinist who loves engines and this was a really well done video. 👍🏼👍🏼

[@Poly318]

@IndridCool54, I appreciate your feedback. Thanks.

[@NipkowDisk]

Thanks a million for covering this series!

[@MrGlenferd]

I put a 66 or 67 poly 318 into my 70 fargo. Got a big older 4 speed truck transmission and. Bell housing. It bolted together except for one main bell housing bolt that didnt line up. Ran it for a decade like that. Was a great combination.

[@mylanmiller9656]

i really appreciate what you did, the Mopar A engine is an important part of Mopar history!

[@heathmcinerney4995]

The Poly 318 is an awesome engine. Thankyou for your factual and sensible video.

[@donaldperrotta8514]

My dad bought a new 59 Plymouth Savoy with a poly 318 & automatic push button transmission … motor & transmission were bullet proof reliable !!!!

[@Troy440Dodge]

There's enough quality information in the video. Makes an old Mopar man like me appreciate my automotive choice even more. Subbed instantly!

[@Poly318]

Thanks!

[@paulpaul8953]

I bought a nice original '58 Plymouth Plaza sedan a few years ago. Not being a MOPAR guy, I knew nothing about 50s Plymouth engines. I have been nothing but impressed with the 318 two barrel engine. It is reliable and powerful, a lot of fun to drive!

[@davef.2329]

Great video and trip down memory lane. I had a poly-318 Coronet in high school and it was very reliable, economical, and took a helluva beating, but kept on ticking (literally).

[@UncleTonysGarage]

Nice video, but two things... The term "Semi Hemi" didn't come around until the middle 60's and it was applied to Big Block Chevy engines who were then competing against the 426 Hemi. Chrysler only referred to the Poly's as "single rocker shaft engines" when they were in production. As for them being cheaper, yes the quality of the components was top notch, but they had fewer parts and less metal overall, Chrysler was able to save on the second set of shafts, the rocker shaft stands and their machining, the pushrod tubes etc. They were by no means "cheap" engines, just cheaper than the Hemi.

[@eugenepolan1750]

If you say "Less Expensive" rather than "Cheaper", it doesn't have a negative connotation.

[@Poly318]

Thanks for the comments. While Chrysler Corporation never referred to the Hemi-block poly as a "semi-Hemi," the earliest evidence of the term I have found is long before the Chevy reference. I located a microfiche 1958 Los Angeles Herald Examiner classifieds ad from an auto wrecker advertising "running Dodge and Chrysler semi hemispherical motors." The period hot rodders I have spoken with who were building Hemis in the late 50s and early 60s also confirm that they were using the moniker when buying Hemi-block poly engines for parts. When someone would say they picked up a 354 it was assumed to be a Hemi, so they would say, "I picked up a 354 semi-Hemi" to clarify it was a poly head. This newspaper and personal sources are from Southern California, so the term may very well have been regional to where other regions were not calling them sem-Hemis until the 1960s. There was no similar need to differentiate the A-block since it was unique. They and all period sources I've found referred to it as either a Plymouth [displacement] or a poly [displacement], such as a Plymouth 318 or poly 318. From the internal Plymouth documents written by the Qualimatic Mound Road plant engineers and by Plymouth's Finance Department, almost all of the savings in the A-block came from the plant and production process design versus hard parts. While there was minimal savings in a lighter engine block and the single rocker-arm assembly design, the automation coupled with the extremely precise machining tolerances they were able to produce ended up allowing them to build far more engines per hour than the Hemi and Hemi-block poly and with less errors that created factory waste and less warranty issues from dealerships. Two prime examples the A-block design, factory, and finance team give in 1955 documents are the automation of torqueing the head bolts by machine and the cylinder head line. The A-block's head bolts were torqued by machine and had an excellent record of not having leak issues, whereas the Hemi and Hemi-block poly engines were done by hand and would result in human error and head gasket leaks. The other example is how the A-block design team and equipment suppliers invented a single machine to process the cylinder heads that only clamped the head once the entire process, whereas Chrysler Corporation 6 and 8 cylinder heads prior to the A-block including the Hemi and Hemi-block poly required 3 to 4 separate machines and multiple clamping/unclamping actions of the head to process it that introduced stacked tolerances and resulted in junk heads the factory had to either take off the line to repair or scrap. The A-block factory and design applies these similar concepts to every aspect of the engine plant, which resulted in both superior machining and savings.

[@Wiencourager]

All of the poly heads were called semi hemi. Had nothing to do if the block was the same as a hemi engine or not. Chrysler usually referred to them as dual or single rocker shaft. Hot rodders called them semi hemi or poly engines, later on mostly to differentiate them from the later wedge engines.

[@moparnut6286]

​@@Poly318... Pay no mind to uncle caveman he's just a hack pretending to be knowledgeable. Any one can search and be a keyboard expert.

[@JackF99]

Ford Boss 302, 351Cleveland, and 429/460 were the same way too, eh?

[@donaldlong9259]

I have one of these rebuilt sitting on a stand in my conex box. Even picked up a dual carb intake for it. garage art!

[@mickangio16]

Need something cool to put it in👍

[@petergrey7125]

Lol! I just picked up and dual quad intake for mine. Hard to find.

[@petergrey7125]

Great video with great content. I have a 66 Plymouth fury convertible that has the 318 A block. Could change it out but I like the idea of keeping it original to the car. Part of the fun is finding parts for it and making it run well enough to keep up with the big blocks. Please keep up the great and informative videos . 👍

[@alanpearce9071]

Our family had a slew of 318's. '59 Suburban with a Torqueflite and a gas heater, a '60 Dart Pioneer w/ Powerflite, a '64 Savoy w/ Torqueflite, a '64 330 w/ Torqueflite, and a '63 440 w/ Torqueflite that I did change the intake to a 4bbl.

[@chuckwhitson654]

I put an old 318poly into my buddy's ram charger. It has a ton of wear and tear on it but smoking a little, a quart or quart and a half a week of oil and he kept it awhile

[@race8427]

It would have been nice to see further development done on the poly heads.

[@hoost3056]

They could have made the Poly a beast if they wanted to but it's a marketing thing. It wasn't meant to overshadow the B and the Hemi .

[@adotintheshark4848]

develop a 4-valve setup

[@mrdanforth3744]

The 318 was overshadowed by the bigger B engine for performance. The 318 had a lot of potential that was never developed.

[@chasefell4234]

I have a 66 Travco with original Poly 318-3. This engine pulls the coach quite well. I have the hydraulic lifters and the 4V carburetor. . I can make the case that the A engine cools better because of the mass of the heads. Long live the Poly. Great video BTW.

[@TimGrimes-q2q]

great content, I worked at mound rd engine and other big 3 plants as an outside contractor doing concrete form work. I look foward to more of your videos, thank you

[@Poly318]

Thanks for your support. After researching the Mound Road plant, I would love to have toured it before its demolition. I guess I could see if Stellantis will let me stand it the parking lot that now covers the old plant to see if an aura exists 😆

[@TimGrimes-q2q]

@@Poly318 you didn't miss much. mound rd engine was a dump, low ceiling, i could never have punched into that plant for 30 yrs, i worked at warren truck and stamping and i had to drag up for outside work cuz i needed fresh air. i look forward to more of your videos. My dad was a district manager for Dodge from 67-73 and he had excess to any ride he wanted back then, he had a 70 RT/SE convertible with a 383 mag and he let me sit on his lap while he did whole shots in the under construction neighborhood and mom had a 340 4 speed , those were the days, i never have seen a 318 poly but it sounds like TCC should have run with it, just imagine a 340 poly

[@michaelwallbrown3726]

i have a polyhead 318 in my 1965 Coronet 440 ragtop i love it for it's uniqueness and dependability would get it rebuilt if anything would happen to her

[@adotintheshark4848]

The LA 273 could be had in the '65 Plymouth Valiant and Barracuda. That's probably the earliest use of that engine. Also, I owned two vehicles that had the A-318. A '62 Dodge Power Wagon 4x4 and a "65 Belvedere I inherited from my parents. Both were high mileage and both used a little oil, but didn't break down. Excellent, informative video I might add!

[@Poly318]

@adotintheshark4848, thanks. The 1965 Belvedere has wonderful lines. The LA273 was released for the 1964 model year optional in Plymouth Valiant and Barracuda and Dodge Dart models. The 273 Super Commando was released in 1965, which is a great engine and the start of factory performance LAs.

[@jimstrict-998]

​@@Poly318 273 Super Commando usually referred to as the "Formula S".

[@soilwork1981ify]

My 66 Dodge Cornette 500 2 door had the 318 poly.

[@adotintheshark4848]

65-66 Belvederes and Coronets were beautiful, under-appreciated cars, especially the hardtops.

[@felonysounds]

My dad bought a 55 4 door savoy 6 cylinder, bought a 56 4 door for parts that had a V8, it's a poly with dual points and I believe a 2 barrel or single barrel 🤷 has spark but could never get the poly V8 to fire. My dad passed in 2016, we still have the 55 savoy and the poly V8 and transmission is still bolted to it. Always had plans of putting the V8 into the good car, only thing savable from the parts car was motor, trans and glass, hood and trunk and doors

[@jeffalan6339]

Who says the Internet cant be informative? I onow 340 wnd 340 6 bbl and 440 also 5440 6 bbl a hemi owner addition ally 413 ramcharger. Thid video provided more info than all thoe mopar guys. Todays engines are all about technology and fuel efficiency Back then romp and stop gastest car wins. My old nova SS installed 406 SB lunati racing cam it would turn completely sideways from dead stop get 13 on the highway ,17 in town. I long fit yhe day of hemi charger 440 6pk sioer bee 440 corner RT Even 340 duster

[@markanderson1519]

Great video. One of the interesting things that I noticed is that some poly engines have a much more pronounced sawtooth shape to the valve covers than others. I wonder if the big sawtooth poly's are the semi-hemi engines or if there is some other explanation.

[@Poly318]

@markanderson1519, thanks. Yes, the Dodge/Chrysler Hemi-block poly heads have four very deep, symmetrical waves in the heads and valve covers pictured at 0:30. On the other hand, all A-block heads have a shallower sawtooth wave pattern with four peaks like my head at 0:20.

[@michaelgautreaux3168]

👍👍 Many thanx.

[@hoost3056]

The Poly came back in the modern era as the 4.7 SOHC V8. The principle was the same. I will say this......the Poly has one of the best sounds ever produced by a V8. There's a stroker on KZbin that will make you smile.

[@rossawood5075]

I owned an Australian assembled right hand drive 1959 Desoto Firesweep, it would have been a 1958 equivalent in US and Canada, it was fitted with a 361 cu block that if I remember correctly developed a claimed 309 bhp, it had a push button torqueflite auto, air and steer, however the air was not factory but a very neat aftermarket wide slim underdash unit. A light green with dark green top and those beautiful 3 bullet tail lights on each fin, the Desoto had the best looking front grille and rear tail styling of the forward look Chryslers IMHO.

[@79tazman]

My grandfather worked for Chrysler in Windsor his first job was the engine plant not sure what year he started but it was in the 50's for sure when he retired he worked in the big van plant on Pillette Road he also worked in the main plant back in the 70's when they were building the Cordoba's and the Lil Red Express trucks.

[@angieshaw8877]

Whatever happened to the Cordova?... MoPars answer to GM/Chevy MonteCarlo ...both of the early-mid 70s... @lds/aes

[@bobroberts2371]

One data point. I have a 1956 Plymouth with a 277 / Powerflight. Decades ago the crankshaft broke under another persons ownership and the car was sidelined. From what I understand, broken cranks on the 277 were an issue.

[@michaelsmith8467]

I didn’t know the 318 was so versatile. I had a Sport Fury with a 318. I had the misconception it was just a dog without redemption. Swapped a 383 commando B block which was difficult to do. Although it had better performance the chassis just was not up to the job even after installing beefier torsion bars, leaf springs, and sway bars off a police cruiser. I needed the B chassis K member. Way to much work to swap out in the day.

[@ImNotHereToArgueFacts]

Had a '66 Belvedere 318 in '82 The interior was trashed and someone primered it brown looked like with a paint brush. It was hideous I tried to blow it up and burnt up 2 tires. I filled it hose water trying to freeze crack it. Grandad replaced the tires and freeze plug 6 months before died. I inherited his '77 Ford F150 351M and gave the car to my cousin. Wish I still had both today

[@tomlewis4345]

We had a 59 Plymouth wagon with the 318 in it and you couldn’t keep main bearings in it. It ran pretty good and was pretty quick but the front sump oil pickup starved the oil pump under hard acceleration.

[@Poly318]

The 1959 A318 wagon engine was a center sump oil pan, and a front-sump pan won't clear the crossmember. Only trucks and some industrial A-blocks received a front sump, and that design was used through 1967 without widespread reports of oiling issues. The A-block cars used the 4-quart center-sump design from 1959 - 1967 with no reputation or service bulletins of oiling problems with the pan/pickup, so I suspect something else was wrong with the engine.

[@tomlewis4345]

@@Poly318 Ithink it was something other than the oil sup because of other 318s would live forever and rattle like a junk yard.

[@daveallen8824]

It would be interesting to know the logic behind the 313 - to make a separate engine line (at least the boring operation) for a difference of just 5 cubic inches? Had to have been a compelling reason.

[@mylanmiller9656]

What I always wondered was how come Mopar stuck with the 318 instead of the larger bore 326 dodge engine.

[@herman452]

Good overall presentation, but the 56 Fury 303 did not get its extra inches just from a .060 overbore, but also from an increased stroke. The Fury 303 essentially had what became the 318 crank, with a 3.31 stroke compared to the 277's 3.13 stroke. Then the 57 301 had a 318's 3.91 inch bore with a 277's 3.13 stroke. Etc., etc.

[@Poly318]

Correct, the A303 has a 3.81" bore and 3.31" stroke, whereas the A277 has 3.75" bore and 3.125" stroke. I have a full list of the specs if anyone is interested in seeing the comparisons at poly318.com/poly-318-engine-specifications/ Thanks for the comment.

[@milkyperformance]

why is the 315 truck engine always left out of these lists ??

[@Poly318]

The 315 is not in the A-block engine family that this video covers but is in the first-generation hemi-block family. It's a very different engine than the A-block polys.

[@garymckee8857]

Timing Chains fit 318, and the early Chrysler Hemi

[@JosephCowen-ru7up]

Did I miss the bit on the 273 LA or Low Deck A engine ?

[@Poly318]

You did not. There was never a "low deck" or "raised deck" A-block since only one deck height was used for the 1956 - 1967 A-block at 9.603", plus or minus a few thousands depending on machining tolerances. The 273 is based off the A-block short block but is in the Light A (LA) engine family and not the focus of this video. I mention the LA273 around 15:11 as an aside but don't go into much detail.

[@alexgrindnshine2522]

These poly engines are really cool. Not sure how many people know that the modern 4.7L sohc engine has valve placement that looks almost identical to these old poly heads. I wish Chrysler would have kept with this design. Were they the first to bring this canted valve arrangement to the market out of the big three? Will Poly heads bolt onto an LA block?

[@Poly318]

@alexgrindnshine2522, yes, Chrysler Corporation pioneered what they named the polyspherical valve and chamber arrangement at the time GM was experimenting with the wedge arrangement in the small block and Ford with the peanut-shaped chamber in the Y-block, both with inline valve configurations. A-block heads can be fitted onto an LA short block, but it's not a direct interchange and much more work than simply using an LA 2.5" main journal crankshaft in the A-block for stroking. Most of the A-block's coolant ports are either missing or misaligned and need to be drilled into the LA block for optimal cooling. A-block heads use two oil drain-back galleries drilled through the head down through the block into the crankcase that the LA doesn't have, so you either need to rely on the A-block intake push rod holes for drainage--which keeps a quart or more of oil tied up in each cylinder head for it to pool high enough to reach the push rod holes--or you have to tap into the A-block's head and run drain-back lines into the oil pan. The LA block up toward the deck needs to be ground for A-block push rod clearance. LA flat-top pistons will either need to have valve reliefs cut in to match the A-block intake valve, or A-block pistons can be fitted. An A-block camshaft must be used, which fits without modification. Either A-block or LA lifters can be used, although A-block lifters are shorter.

[@alexgrindnshine2522]

@@Poly318 thank you for all the great info.

[@Poly318]

@alexgrindnshine2522, I'm happy to share.

[@jarepair7429]

They forgot to mention the self driving 1958 model named Christine.

[@trickyricky12147]

Haha yeah

[@jonathanmorrisey5771]

Where does the 241 cid from 1955 fit in?

[@Poly318]

@jonathanmorrisey5771, the 241 Hemi and Hemi-block poly is not in the A-block family covered in this video.

[@davidpowell3347]

@@Poly318Did 1955 Plymouth offer both "poly" based on the Dodge hemi block and "poly" based on the new A block?

[@Poly318]

@davidpowell3347, no, the A-block was not offered until the 1956 model year. 1955 Plymouth used the Dodge V8.

[@wildcat650power]

I had to 🛑 and say something. Just because the engine did not have the early "Hemi" heads like the early engines, does not mean it's not a semi Hemi. They are indeed a semi Hemi. The heads have a hemispherical computation chamber thus semi Hemi. The same was for the Australian slant 6'ers. The old guys didn't say they are a full on Hemi...thus "semi Hemi" was the term used.

[@louislepage5111]

Its a crying shame that Chrysler didn't develop this engine further performance development 😮

[@kevinsparks1279]

I have a 57 dodge one ton dually with what I thought was a 315ci. poly. Is it a 313? I really like it and feel like it's a rare find and hope to get it restored. Dodge all the way!!!!

[@Poly318]

@kevinsparks1279, domestic Dodge trucks did not receive the A-block until 1959 with the A318. Export trucks offered the A303 in 1957 and then the A313 starting in 1958. The A-block is easy to tell apart from the Hemi-block poly. If your engine has valve covers with four very deep and symmetrical scallops, it's a Hemi-block poly. If your engine has four shallow and asymmetrical scallops, it's an A-block. There are many other differences, but the valve covers are easy giveaways. Another easy one is that the A-block has an intake manifold that seals the valley, like an LA or small block Chevy intake manifold, whereas the Hemi-block poly uses a separate valley cover underneath the intake manifold with a gap between them.

[@jimstrict-998]

​@@Poly318The red 315 Dodge truck engine pictured for 1959 is a true hemi.

[@hotrodray6802]

The B block was introduced in 1958 at 350 cubic inches.... In 59 grew to 361.

[@jimstrict-998]

Another correction is for the 1959 361 Golden Commando. That would be 395 gross TORQUE, rather than HP, unless we're talking about a dual-quad version.

[@Poly318]

@hotrodray6802, The B350 and B361 were both available in 1958.

[@Poly318]

@jimstrict-998, You're correct. I meant to say ft.lbs. torque, but horsepower snuck out. They were advertised 305 HP. Thanks for pointing that out.

[@mylanmiller9656]

the reason for the development of the LA engine was, Mopar needed a V8 engine to fit into the compact Valiant and Dart. it is too bad they didn't continue development of the poly engine; the Ford 351 Cleveland is a copy of this head design and it proved to be the best power to ci engine with all modern engine layouts copying it. Mopar could have been first to the water hole if they had continued developing the Design.

[@jammerz63]

He forgot the 325 dodge.

[@Troy440Dodge]

The Dodge 325 Red Ram is covered.

[@Poly318]

I discuss the A-block Dodge Red Ram 326 at 09:00 minutes. The Dodge 325 is a Hemi and Hemi-block poly engine and not in the A-block family discussed in this video. The A-block version was a 324.49 c.i.d. advertised by Dodge and listed in service manuals as a 326 to differentiate it from the Hemi and Hemi-block poly 325.

[@Troy440Dodge]

@@Poly318 My mistake on the engine identification. As a retired mechanic specializing in Mopars, I've encountered only two 325 Dodge engines. I will admit that the 318 is the toughest engine ever built. In all generations. And one of the most underestimated as a performance build.

[@deanstevenson6527]

🥝✔️

[@ericwilson2585]

Well these Chrysler poly engines are as confusing as all the different engines Ford produced....

[@raginroadrunner]

Chrysler shot themselves in the ass when they dropped this motor. Bad bad move.

[@TheJCompound]

Mopar!