Mopar 273 Engine Specs

Intro

➤ See the Family Page for specs common to all engines in this family.

The Mopar 273 is where the LA small-block story actually starts. Before the 318 became the engine everybody had, before the 340 started collecting trophies and inflated asking prices, and before the 360 discovered torque, Chrysler built a little 273-cubic-inch wedge V8 for cars that needed more engine without hanging an anvil over the front suspension. Introduced for 1964, it was the first production LA and the clean break from the broad-headed A-series Poly that came before it.

The important word is little, and there is no insult in it. The 273 used a 3.625-inch bore and roughly 3.31-inch stroke, which gave it the smallest bore in the LA family and a personality built around light cars, clean response, and willingness to rev rather than brute-force torque. Put one in an early Dart, Valiant, or Barracuda and the whole idea makes sense. Put one in something heavy and start asking for 360 behavior, and physics will eventually ask what everybody has been drinking.

Base two-barrel versions were honest transportation engines. They gave Chrysler’s compact cars smooth V8 manners without turning every trip to the grocery store into a tuning exercise. In a light A-body with decent gearing and a healthy ignition system, even the ordinary 273 could feel crisp because the car was not asking 273 cubic inches to drag half the county behind it.

Then Chrysler showed what the little engine could do when somebody stopped ordering it for sensible people. Commando and Charger 273 versions added higher compression, four-barrel carburetion, hotter cam timing, stronger valve springs, dual exhaust, and enough factory attitude to make a light Barracuda or Dart considerably more interesting. The commonly listed 235 horsepower was serious output for a small V8 in that package, and the engine did not need another sixty cubic inches to make its point.

The rare 1966 D/Dart took the 273 farther into factory drag-racing territory with an even more specialized combination. That is also where today’s nonsense starts. A four-barrel, louder exhaust, and enthusiastic owner do not convert an ordinary 273 into a Commando, Charger, or D/Dart while nobody is looking. The hotter the claim, the more parts, dates, vehicle context, and documentation need to quit mumbling and agree.

The 273 also carries some early-LA peculiarities that punish anybody who assumes every Chrysler small-block part was designed at the same meeting. Early intake-manifold bolt arrangements, crank-register details, transmission hardware, front dress, and other year-specific pieces need checking before somebody orders a pile of later 318 and 340 parts because “it’s all LA stuff.” Family resemblance gets the parts into the garage. Measurements decide whether they stay.

For a restoration or period build, the 273 has a strong reason to survive. It belongs in the early cars that introduced Chrysler’s new lightweight V8 architecture, and a correct Commando, Charger, Formula S, or other original application loses something when the little engine gets tossed aside simply because a 360 makes more torque.

For a clean-sheet horsepower project, though, sentiment needs to know when it has lost the argument. The small bore limits breathing, valve size, piston choices, and easy displacement. Machine work costs just as much on 273 cubic inches as it does on something larger. Build the 273 because the car deserves one or because a sharp little early LA is exactly what you want. Do not build one because somebody convinced you the smallest engine in the family is secretly the cheapest road to big power.

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Overview

Chrysler created the 273 because its new compact cars needed a V8 better suited to their size than the old A-series Poly. The Poly had done good work, but its broad heads and heavier package were not exactly ideal when the engine bay belonged to a Dart, Valiant, or Barracuda. The LA design kept useful Chrysler small-block fundamentals and replaced the wide polyspherical top end with a narrower wedge-head arrangement. The result was lighter, easier to package, and considerably less likely to make the front suspension feel personally insulted.

The 273 used a 3.625-inch bore and roughly 3.310-inch stroke for 273 cubic inches. Bore spacing was 4.460 inches, deck height roughly 9.600 inches, and the familiar LA architecture included a cast-iron block and heads, five main bearings, in-block camshaft, pushrods, shaft-mounted rocker arms, and rear-mounted distributor. The engine was internally balanced in normal factory form and used 2.500-inch main journals and 2.125-inch rod journals.

That 3.31-inch stroke is important because Chrysler kept essentially the same short-stroke geometry when it developed the 318 and 340. The major difference was bore. The 273 starts at 3.625 inches, the 318 grows to 3.910, and the 340 stretches all the way to 4.040. The crank throw stayed familiar while Chrysler kept carving larger holes in the block until airflow finally had room to stretch its legs.

That makes the 273’s small bore both its defining feature and its natural limit. Smaller cylinders restrict valve diameter and breathing room compared with the later engines. None of that stops a 273 from making respectable power. It simply means the builder cannot order 340-sized airflow expectations and expect the cylinder walls to move out of courtesy.

In ordinary two-barrel form, the 273 was designed for smooth, useful V8 power in relatively light cars. Factory ratings commonly hover around 180 horsepower depending on year and specification. That does not sound dramatic until the engine is placed back into the compact Mopar Chrysler actually designed around it instead of compared with a modern crate engine on a sheet of paper.

The small displacement rewarded light vehicle weight, sensible gearing, clean ignition, and an engine combination that was not trying to impress everybody at the cruise night with carburetor size. Too much camshaft, too much carburetor, low compression, and tall gears can make a 273 feel remarkably weak. That is not the engine failing. That is 273 cubic inches filing a complaint against the parts list.

The Commando and Charger 273 packages showed the other side of the engine. Higher compression, four-barrel induction, hotter solid-lifter cam timing, stronger valve springs, dual exhaust, and other performance pieces raised output to the commonly quoted 235-horsepower range. In a light Barracuda Formula S, Dart, or similar application, that combination gave Chrysler a genuinely sharp little performance engine before the 340 existed.

Its character was different from the larger LA engines that followed. The 273 did not overwhelm a car with torque. It liked revs, gearing, and low vehicle weight. When the whole combination worked together, the engine felt lively rather than massive. Anybody expecting a little-block version of a 440 has misunderstood both ends of that sentence.

The 1966 D/Dart represented the narrow factory-racing end of the 273 story. Commonly associated with a 275-horsepower rating and more aggressive competition hardware, it deserves its own proof standard because very few engines become rarer after spending sixty years around hot rodders unless somebody starts inventing additional survivors.

A genuine D/Dart claim therefore needs the car and engine to support one another. Correct application, induction, camshaft, exhaust, drivetrain context, date information, and documentation matter. A normal four-barrel 273 can be a perfectly desirable performance engine without being promoted into a factory drag package because the seller found an old magazine article.

The same caution applies to Commando and Charger claims. Intakes, carburetors, valve covers, distributors, and exhaust pieces all move easily enough after decades of ownership. A 273 wearing good equipment today may simply be a well-modified 273. That can make it more enjoyable without rewriting what Chrysler assembled.

Early production also brings one of the 273’s most famous parts traps. Early 1964–1965 heads use intake-manifold bolt details that differ from later LA practice. A later LA intake may look like it belongs right up until the bolt holes start explaining otherwise. Verify the heads and bolt arrangement before buying the manifold. Aluminum has no moral obligation to fit merely because the catalog said “LA small-block.”

Crank-register, converter, flywheel, transmission, and related hardware also deserve year-specific attention. Early Chrysler small-blocks were built during an era when engineers were still perfectly willing to change details before future restorers had organized their socket drawers. A transmission may share the general small-block pattern and still need the correct crank, converter, starter, and related pieces before anything useful happens.

Front dress can create the same kind of grief. Timing covers, pulleys, water pumps, brackets, accessory drives, and linkage evolved as the family matured. Keeping original 273 hardware together is often far cheaper than throwing it into separate boxes and later discovering that one ugly bracket was apparently manufactured from unobtainium.

Compared with the LA 318, the 273 shares the basic short-stroke family architecture but gives away substantial bore and displacement. The 318 is easier to build for general street torque and has a broader parts history. If originality is irrelevant and both engines are sitting equally complete on the floor, the 273 needs a reason to win.

Compared with the 340, the difference is even clearer. Both share roughly the same stroke, but the 340’s 4.040-inch bore gives it dramatically more breathing room and lets Chrysler use larger valves and more serious performance hardware. The 273 helped prove the LA platform could perform. The 340 later demonstrated what happened when Chrysler gave that architecture considerably more cylinder.

Compared with the 360, the 273 belongs to an entirely different personality. The 360 uses a much longer 3.580-inch stroke and considerably more displacement, making it naturally better suited to torque and heavier vehicles. Asking which is “better” without mentioning the car is like arguing whether a ball-peen hammer is better than a sledgehammer. Try driving trim nails with the sledge and report back.

That is why a good 273 usually deserves to remain a 273 when the vehicle gives it historical context. An early Barracuda, Dart, Valiant, Formula S, Commando, Charger 273, or similar car can lose some of its identity when the original little engine is replaced simply because more cubes were available behind the next garage.

A sensible street rebuild should work with the engine instead of fighting it. Healthy compression, modest camshaft, properly sized carburetion, clean ignition, free exhaust, and gearing appropriate to a light car can make a 273 crisp and entertaining. The engine responds far better to a matched combination than to somebody throwing the largest available parts at it and waiting for displacement to appear.

Condition still decides whether the project is worth doing. The small bore makes cylinder wear, rust, previous overbores, and remaining wall thickness especially worth inspecting. Add cracked castings, worn lifter bores, damaged exhaust ears, missing manifolds, hacked linkage, tired valve gear, and questionable old machine work to the usual list. A rare or correct block does not become healthier because everybody wants it to be.

Parts availability is manageable, but the 273 is not the LA family’s easy button. Pistons, rings, early intake hardware, valvetrain pieces, exhaust, brackets, pulleys, linkage, transmission fit, and other early components need more deliberate shopping than a common later 318 or 360. Missing early parts have a special talent for becoming valuable shortly after somebody discovers they are missing.

For pure horsepower-per-dollar work, the larger LA engines usually win. The machine shop does not charge by cubic inch, and the 273’s small bore starts the build with less airflow and less displacement before the first dollar leaves the wallet. Spending heavily to make a 273 behave like a 340 can become a very expensive demonstration that Chrysler already built a 340.

The 273 therefore makes its strongest case through context and character. It started the LA family, fit Chrysler’s early compact cars beautifully, produced some legitimate factory performance packages, and showed that a small wedge-head Mopar could be sharp without being large. Build one because that is the engine the car deserves or because a rev-happy early LA is exactly the point. The little engine does fine when nobody asks it to apologize for being 273 cubic inches.

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General Specs

Displacement	273 cu in / 4.5L	Bore / Stroke	3.625 in × 3.310 in
Production / Use Era	1964–1969 early Mopar LA small-block passenger-car era	Bore Spacing	4.460 in
Engine Family	Chrysler / Mopar LA-series small-block wedge V8	Deck Height	9.600 in LA small-block baseline
Block Material	Cast iron	Rod Length	6.123–6.125 in LA small-block baseline
Cylinder Head Material	Cast iron	Main Journal	2.500 in
Factory Rating	Base 2-barrel commonly listed around 180 hp; Commando / Charger 273 4-barrel versions commonly listed around 235 hp; 1966 D/Dart package commonly listed around 275 hp	Compression Ratio	Version dependent; verify by exact year, pistons, heads, and package
Fuel / Induction	Gasoline; carbureted, 2-barrel or 4-barrel by version	Rod Journal	2.125 in
Cam Location	In-block camshaft	Main Bearings	5
Valve Layout	OHV / pushrod, 2 valves per cylinder; wedge chambers	Firing Order	1-8-4-3-6-5-7-2
Common Main Caps	2-bolt	Distributor Rotation	Clockwise
Rear Main Seal	2-piece	Balance	Internal balance
Weight	~500–550 lb complete iron LA small-block, depending on accessories/configuration	Dimensions	~28H / ~26W / ~29L
Primary Identity Check	Early LA 273; verify bore, intake bolt angle, crank register, castings, stampings, and original application	Common Torque Range / Strength Lane	Light-duty small-cube torque lane; crisp in light cars, not a cheap big-torque substitute for 318 / 340 / 360 builds

Verify the block, bore, crank, heads, intake pattern, intake bolt angle, carburetion, camshaft, compression, converter or flywheel fit, front dress, stampings, and vehicle application before ordering parts. The 273 is an LA small block, but early LA does not mean every later LA part gets to march in and behave.

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Variants

The 273 starts the LA story, and Chrysler gave the little engine three useful factory personalities: the ordinary two-barrel version, the hotter Commando / Charger four-barrel package, and the rare 1966 D/Dart competition engine. Same 3.625-inch bore and roughly 3.31-inch stroke underneath, but the induction, compression, camshaft, exhaust, and factory purpose changed enough to matter.

Standard 273 — Two-Barrel

What it was: This was the everyday 273, built to give early Darts, Valiants, Barracudas, and other compact Mopars smooth V8 power without hanging unnecessary weight over the front wheels.

What changed: The standard engine used two-barrel carburetion, modest compression, conservative cam timing, and street-oriented exhaust around the new wedge-head LA architecture.

What that did: In a light A-body, 273 cubic inches were enough to make the car feel crisp without pretending it had swallowed a big block. The engine liked sensible gearing and clean tuning. Give it too much carburetor, too much camshaft, and tall gears, and the little thing starts wondering why the parts catalog was allowed near the garage.

Where used: Early Dodge and Plymouth compact passenger-car applications including Dart, Valiant, Barracuda, and related models.

Commando / Charger 273 — Four-Barrel Performance

What it was: This was the genuine factory performance version. Plymouth used Commando terminology, while Dodge used Charger language for its hotter 273 applications.

What changed: Chrysler added higher compression, four-barrel carburetion, hotter solid-lifter cam timing, stronger valve springs, dual exhaust, and the supporting performance hardware needed to make the little engine breathe.

What that did: Output climbed into the commonly quoted 235-horsepower range, and the character changed with it. The 273 still did not make big-block torque, but in a light Barracuda Formula S, Dart, or similar car it liked rpm and rewarded a driver who understood gears. Small engine, light car, good breathing. Funny how often that works.

Where used: Performance-oriented Barracuda, Formula S, Dart, and related Commando / Charger 273 applications.

Identification caution: Four-barrel intakes, carburetors, valve covers, distributors, and exhaust parts have spent sixty years changing owners. A real Commando or Charger 273 claim needs the correct engine, compression, camshaft family, carburetion, distributor, exhaust, application, dates, tags, and documentation. A four-barrel proves somebody owns a four-barrel.

1966 D/Dart 273 — Factory Drag Package

What it was: The D/Dart was the narrow competition branch of the 273 family, built for drag-class work rather than ordinary street performance.

What changed: Chrysler used a more aggressive high-output 273 combination with specialized induction, camshaft, exhaust, and supporting drivetrain hardware beyond the regular Commando / Charger package.

What that did: The commonly associated 275-horsepower rating put the little LA into genuine factory competition territory. Chrysler was no longer asking whether the 273 could make a Dart entertaining. It was asking whether the other lane could keep up.

Where used: Rare 1966 Dodge D/Dart drag-racing package.

Identification caution: D/Dart claims deserve the hardest proof in the 273 family. Correct vehicle identity, engine hardware, induction, camshaft, exhaust, drivetrain, dates, original equipment trail, and documentation all need to agree. Rarity is not a substitute for evidence. It is the reason to demand more of it.

Early 273 hardware also deserves attention because Chrysler had not yet finished standardizing every LA-family detail. Intake-manifold bolt angle, head configuration, crank register, converter or flywheel fit, front dress, and year-specific pieces can differ from later 318, 340, and 360 hardware. “It’s all LA” is a fine sentence right up until the bolt holes disagree.

So the real 273 variant map stays clean: standard two-barrel, Commando / Charger four-barrel performance, and the rare D/Dart competition package. The 273 was small because Chrysler designed it for light cars, not because the engineering department forgot how to measure cylinders. Give it the right hardware and the right job, and the little engine does not need to apologize to anybody.

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Key Notes

The LA 273 is the first of Chrysler’s lightweight LA small blocks, not an A-series Poly, not a later LA 318, and not a tiny 340 waiting for a decal to make it important. It matters because it started the LA path, but starting the path isn’t the same as being the strongest engine on it. That difference keeps people from spending 340 money on 273 results.

The basic fingerprint is 273 cubic inches from a 3.625-inch bore and 3.310-inch stroke. The stroke is shared with the 318 and 340, but the small bore changes the whole conversation. It limits valve size, breathing room, piston choice, and how much lazy 318 / 340 thinking the engine will tolerate before it turns into a wheezy little lesson.

The 273 is easy to misidentify because Mopar small blocks share enough family shape to fool people who stop at valve covers. Casting numbers, bore measurement, date codes, intake bolt angle on early engines, crank register, converter or flywheel details, and original application all deserve a look. “Small-block Mopar” isn’t a parts list.

Early 1964–1965 273 engines can have their own intake-manifold headache. The early LA intake bolt angle and bolt size can differ from later LA small-block assumptions, so a later intake doesn’t automatically bolt on like the catalog shortcut promised. This is one of the classic 273 ways to waste time: buy the part first, learn the angle later, then explain why the engine is still sitting open.

The Commando and Charger 273 stories need proof. The base 2-barrel 273 was a small, smooth, useful V8. The hotter 4-barrel versions got better compression, cam, induction, dress-up pieces, and more attitude. Those parts can be swapped, cloned, lost, or faked. A 4-barrel intake and shiny valve covers don’t prove the engine was born special.

The 235-horse 273 was real, and it gave early A-bodies a sharp little engine with more personality than the displacement suggests. That doesn’t make every 273 a Commando, and it doesn’t make every Commando claim worth a premium. The block, date trail, induction, valve covers, distributor, compression, original car application, and paperwork need to agree before the seller’s grin gets paid.

D/Dart-style claims need even more suspicion. Race-oriented hardware, special induction, camshaft, exhaust, and limited-production context can make imaginations sweat. Don’t buy a D/Dart fantasy because somebody found a 273 with a 4-barrel and a loud exhaust. Rare package claims need rare-package evidence, not volume and confidence.

Application context matters. In an early Barracuda, Dart, Valiant, or other correct small-body Mopar, a 273 can be a neat, right-sized engine that keeps the car’s original character. In a heavier car or a generic street build, the small cubes show up fast. The 273 likes light weight, gearing, compression, clean ignition, and matched parts. It doesn’t like being asked to act like a 340 after lunch.

As a restoration engine, the 273 can be worth saving when the car calls for it. A correct early A-body with its proper 273 is different from a loose core somebody wants to price like rare jewelry. The engine has historical value, originality value, and early-LA charm. It doesn’t automatically have big-dollar performance value just because it’s less common than a 318.

As a performance platform, the 273 is usually the hard way to do a job a 318, 340, or 360 handles easier. The small bore limits breathing, and the aftermarket isn’t built around making the 273 everyone’s favorite shortcut. If the goal is a period-correct little engine that revs cleanly and feels right in a light car, fine. If the goal is cheap power, the bigger LA engines are already laughing from the corner.

Parts support is manageable, but it isn’t idiot-proof. Pistons, rings, early intake fitment, solid-versus-hydraulic valvetrain details by year and version, timing pieces, exhaust manifolds, brackets, pulleys, valve covers, and kickdown / throttle-linkage details need checking before money leaves the building. Missing early-LA pieces aren’t cute. They’re time thieves with part numbers.

Interchange needs discipline. Some LA parts cross, some require year-specific attention, and some later pieces create more problems than they solve. Don’t assume later 318 / 340 intakes fit 1964–1965 273 heads. Don’t assume every converter, crank, flywheel, or accessory setup matches just because the block is LA-family. Mopar parts can look friendly right up until they make you crawl back under the car twice.

A used 273 core needs the normal old-engine inspection plus the early-small-bore worries. Check for cracks, freeze damage, stuck pistons, rusty cylinders, overbore limits, worn lifter bores, deck damage, broken exhaust ears, missing manifolds, missing brackets, hacked linkage, and prior machine work done by somebody who measured enthusiasm instead of clearance. A small-bore engine with bad cylinders isn’t a bargain. It’s a bill with a crankshaft.

The 273 belongs in the early-LA identity lane first, not the universal performance lane. Verify the bore, year, intake pattern, performance-package claim, and missing pieces before spending money. If the car deserves a 273, build it carefully and enjoy the sharp little Mopar for what it is. If the plan needs easy torque and cheap horsepower, stop trying to make the smallest LA engine do the bigger engines’ work.

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Bottom Line

The Mopar LA 273 is where Chrysler’s lightweight wedge-head small-block story starts. It never had the cubes of the 318, the reputation of the 340, or the torque of the 360, and none of that is a defect. In a light early Mopar, the 273’s job was to be compact, responsive, and willing to rev without dropping a boat anchor between the front wheels.

The standard two-barrel engine is an honest little cruiser. A genuine Commando or Charger 273 adds real factory performance character, while a documented D/Dart belongs in an entirely different price and preservation conversation. Those versions share displacement, not value. One four-barrel intake and a set of shiny valve covers do not promote an ordinary 273 through all three ranks.

The 273 makes its strongest argument in an early Barracuda, Dart, Valiant, Formula S, or other car where the original engine helps define what the vehicle is. Built with sensible compression, camshaft, carburetion, exhaust, and gearing, it can be crisp and entertaining. Ask it to pull a heavy car, swallow too much carburetor, or behave like a 340, and the little engine will expose the bad plan long before it impresses the tires.

For a project starting from loose iron with horsepower per dollar as the only goal, the larger LA engines usually make more sense. The 318 brings easy displacement, the 340 brings the performance hardware and reputation, and the 360 brings torque. The 273 earns its rebuild bill through correctness, early-LA identity, and light-car manners. Small displacement does not make machine work, missing early hardware, or rare-package mistakes any cheaper.

So save a good 273 when the car deserves it, build one sharp rather than oversized in ambition, and make Commando, Charger, or D/Dart claims prove themselves before the wallet gets involved. The 273 does not need to impersonate its bigger brothers. It started the LA family, fits its early cars beautifully, and can be a very satisfying little V8 when nobody asks 273 cubic inches to carry 340 expectations.

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