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

@IndridCool54, I appreciate your feedback. Thanks.

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

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.

I like that you did the proper research and how you explained everything. Seems like they were building very good and efficient engines in the late 50s. Then by the mid 70s the grand fury was getting horrible fuel mileage and had less power. My dad bought one brand new in 1977.

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.

​@@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.

Thanks!

Need something cool to put it in👍

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

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 .

develop a 4-valve setup

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

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 😆

@@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

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

@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.

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

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

@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.

Haha yeah

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.

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

@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.

@@Poly318 thank you for all the great info.

@alexgrindnshine2522, I'm happy to share.

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.

@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.

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

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.

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

@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.

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

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

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

The Dodge 325 Red Ram is covered.

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.

@@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.