Mighty oaks from little acorns grow, it’s been said, and it certainly applies to the 273 cubic-inch V8 introduced by Chrysler in 1964...
1956 Plymouth A Series polyspherical V8
Introduced in 1964, Chrysler’s 273 cubic-inch V8 was the first of the LA series engines, which proved to be one of the automaker’s most long-lived engine families. In fact, the little V8 spawned numerous variants and remained in production well into the 21st century. But the engine’s full history is even longer than that, as the LA was actually based on the A series V8 introduced way back in 1956. But you might never know it, as the A Series was a very different-looking engine with its polyspherical cylinder heads and distinctive scalloped valve covers (above).
Chrysler engineers were assigned the task (program A828) of creating a small, lightweight V8 for the 1964 Dodge Dart and Plymouth Valiant and Barracuda. But as usual at Chrysler, the budget was limited, while the company had invested a bundle in the Mound Road engine plant and the advanced tooling for the A series V8. With no real alternative, the new LA V8 was closely based on the A series architecture, with the same 4.46-in bore spacing. LA was simply an abbreviation for “lightweight A.” The result was a lighter and more compact package of 525 lbs.
Much of the size and weight reduction was achieved by discarding the poly V8’s bulky valve layout and adopting wedge-type combustion chambers similar to the big-block B and RB engines. The new, simplified valvetrain included one compromise: a funny angle between the pushrod and valve lifter (as shown above), but it wasn’t a problem in standard production applications. For the 1964 launch the 273 was equipped with solid valve lifters, and it didn’t receive hydraulics until 1968.
Up-to-date casting techniques and a single-plane intake manifold shaved off a few more pounds. The 273 cubic-inch displacement (273.29, to be precise) was accomplished with a relatively small 3.625-in bore and a 3.31-in stroke, producing a fairly square 1.095:1 bore/stroke ratio. Valve diameters were accordingly petite: 1.78-in intake and 1.50-in exhaust. The crankshaft and 6.125-in connecting rods were steel forgings (from 1967 on, cast iron) while the pistons were cast aluminum.
1964 273 CID 180 hp V8
For its initial application in the 1964 Dart, Valiant, and Barracuda, the 273 was equipped with a trusty Carter BBD two-barrel carburetor and an 8.8:1 compression ratio. That combination was good for 180 hp at 4,200 rpm and 260 lb-ft of torque at 1,600 rpm. But in 1965 a high-performance version (internal designation A861) arrived with a 10.5:1 compression ratio, a Carter AFB four-barrel carb, and a more aggressive camshaft. This one, standard in the Barracuda Formula S and optional in the Dart GT, was rated at 235 hp at 5,200 rpm. Dressed out with a chrome air cleaner and black-crackle valve covers, it’s the engine in the lead photo at the top of this page. At Plymouth, the high-performance 273 was branded as the Commando.
1965 Dodge Dart GT
The 273 CID V8 was discontinued after 1969, but there were already 318 and 340 CID versions in the lineup, and a 360 would soon follow in 1971. The LA series V8 carried on until 1992, when it was redesigned and rebranded as the Magnum V8, and it remained in production through 2003. Meanwhile, a whole string of purpose-built Dodge NASCAR V8s evolved from the original LA architecture. The ultimate LA, if you will, was the Dodge Viper V10 of 1992-2017. While it has 10 cylinders and an aluminum block, it’s still part of the LA family. In its final stage of production development, the Viper displaced 511 cubic inches and made 640 hp.
1992 Dodge Viper V10
273’s got a cast iron crank in 67, but all 273, 318, 340 and 360 engines had forged rods. 318’s got a cast crank in 67 or 68, 340’s got a cast crank beginning in 72 (some 72’s had forged cranks), and all 360’s had cast cranks.
I am the curator of a 1955 Plymouth with the early Hemi based 260 V8. The original dealer sales handwritten paperwork with my car says its 4 bbl carb and dual exhaust makes 277 HP and 250 torque. Those 55 polysphere and the 56+ polysphere really accelerated! Still does.
I had one in my 65 dart, the only problem I had was that a higher that 7200 Rpm If I pushed the clutch in, it would not re engage
One consequence of re-purposing the A series architecture was the LA was physically larger than Ford’s “Windsor” small block which was a “clean sheet” design. In 1967, after taking control of Rootes Group, Chrysler had intended to continue production of the Sunbeam Tiger (then powered by the 289 cid (4.7 liter) Windsor) but with the 273 cid (4.5 liter) LA. Unfortunately, while 4.7 Ford litres filled it to the brim, 4.5 Chrysler litres overflowed; the small-block Ford truly was compact. Allowing the Tiger to remain in production until the stock of already purchased Ford engines had been exhausted, Chrysler instead changed the advertising from emphasizing the “…mighty Ford V8 power plant” to the correct but deliberately vague “…an American V-8 power train”.
Our Chrysler 273 V8 spanked ’em all in the Mobil Economy Runs during the ’60s by consistently topping the V8 classes with superior engineering and the best drivers (and solid lifters). Fun fact:, the same rod bearing was used for the entire A-LA small block range from 1956 through 2003, including the 3.9L V6 (Dakota) and 8.0L V10 (Viper/Truck) engines.
In the late 1980s, Chrysler owned Lamborghini and tasked the Italian engineering team with transforming the LA-based cast iron Dodge truck V10 design into a lightweight, high-performance aluminum engine for the Dodge Viper. Lamborghini’s redesign was so extensive that almost no parts are interchangeable between the iron and aluminum versions. The project was led by legendary Italian engineer Mauro Forghieri at Lamborghini Engineering in Modena…
Mauro Forghieri (1935-2022) was the long-time technical director of Scuderia Ferrari from 1962 to 1984. He designed many iconic cars including the 312 T series, and was crucial to Ferrari winning 4 driver and 7 constructor championships. Credited with introducing the first rear wings in F1 at the ’68 Belgian GP, he is considered one of the last “total engineers’ in Formula 1, capable of designing a complete racing car…
GOIN COMMANDO!
That ‘polysphere’ head looks very similar to the later GM big blocks…396 , 427. 454 etc…I’ve seen them sometimes referred to as ‘ semi hemis ‘…I often wonder if GM was inspired by the poly with their ‘porcupine ‘ mystery motor …
I had a 1967 Barracuda with the 273. The heat riser froze shut and melted a piston. My next car was a 1969 Buick GS 400 4 speed convertible. That was 1 0f 213!
Not enough mention of the 340. This was the ONLY Chrysler engine of the 1960’s solely designed for high performance. Never produced in 2-bbl or single exhaust variants, the 340 completely optimized the LA platform with bigger valves, free-flowing heads, better oiling, and a host of performance tweaks that made its rated 275hp a joke. The NHRA immediately re-rated it to 325hp, and dyno tests of stock 340’s frequently exceeded that. A well-tuned 340 in a light-weight A-body is one of the great combinations of the muscle car era.
This story was deliberately focused on the 273 so we can do stories on the 340 and other variants at a later date. They’re certainly worthy of it.