Mopar 318 Engine Specs

Intro

The Mopar LA 318 is the small-block that did the boring work so well people started mistaking boring for bad. The earlier A/Poly 318 had already made the 318 number familiar, but the LA 318 changed the hardware. Introduced in volume for 1968, this was the wedge-head LA version: lighter, simpler, narrower, and easier to build around than the old Poly-headed A engine. Same displacement. Different engine. Same number, different parts argument waiting at the counter.

Chrysler needed the LA 318 because the 273 had started the LA small-block line, but the company needed more displacement and broader usefulness. The 273 worked in compact cars, but the 318 gave Chrysler a better all-around V8 for compact cars, intermediates, full-size models, trucks, vans, police packages, fleet cars, and about half the vehicles Mopar people drag home while claiming they “just need a tune-up.” It was never meant to be exotic. It was meant to start, pull, survive, and keep the car useful.

That’s where the 318 earned its reputation. In most factory form, it was a two-barrel, hydraulic-lifter, practical small-block built for everyday driving. It didn’t have the 340’s breathing, the 360’s extra stroke, or the big-block’s intimidation. What it had was durability, decent torque, parts availability, and enough simplicity to keep working after flashier engines had already turned into expensive garage furniture. That’s not glamorous. That’s useful.

The wrong assumption runs both ways. Some people treat every LA 318 like a wheezing smog-era lump that should be thrown behind the shed. Others act like a cam, intake, carburetor, and loud exhaust magically turn one into a 340. Both are wrong. The LA 318 has real strengths, but the small bore, heads, compression, camshaft, year, induction, and vehicle weight decide how far the story goes.

The plain-English identity is this: the Mopar LA 318 is Chrysler’s long-running wedge-head small-block workhorse, built for ordinary cars, trucks, vans, and fleet duty more than bragging rights. It’s not the Poly 318, not a baby 340, and not junk because it wasn’t born with a performance badge. It’s the small-block that kept showing up because Chrysler knew it would keep doing the job.

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Overview

The Mopar LA 318 sits in the middle of Chrysler’s small-block story as the engine that made the LA family common. The 273 introduced the lightweight wedge-head LA idea in 1964, but the 318 gave Chrysler the displacement, flexibility, and production life needed to make that family a default answer. It replaced the old Poly-headed 318 in regular U.S. use and carried the 318 number into the wedge-head era, where it stayed for decades in passenger cars, trucks, vans, police service, fleet work, and plain old transportation.

Architecturally, the LA 318 used the same 3.91-inch bore and 3.31-inch stroke dimensions associated with the earlier 318 Poly, but the engine itself was different where it counted. The LA used wedge-style heads instead of polyspherical heads, a narrower package, a lighter layout, and the simpler small-block architecture that made the later 340 and 360 part of the same broad family conversation. That doesn’t mean parts all swap by wishful thinking. It means the 318 became the normal, practical LA small-block foundation. The Poly was the old argument. The LA was the answer Chrysler kept using.

In base form, the 318 was built for service, not hero worship. Two-barrel carburetion, hydraulic lifters, mild cams, conservative compression, and ordinary exhaust made most LA 318s easy to drive and hard to get excited about on paper. That was the job. A grocery-getter Satellite, a Dart, a van, or a half-ton truck didn’t need an engine that acted like every stoplight was qualifying day. It needed one that would start cold, idle cleanly, pull through traffic, and not require the owner to understand valve lash before breakfast.

The LA 318’s strength is balance. It wasn’t as small as the 273, wasn’t as eager or performance-focused as the 340, and didn’t have the 360’s stroke and torque. What it had was enough displacement to be useful, enough durability to survive neglect, and enough parts support to stay alive long after the cars around it started dissolving into driveway archaeology. That’s why the 318 became one of those engines people complain about right up until they need something dependable.

There were sharper versions and later changes, but the label still needs proof. Police four-barrel engines, lean-burn-era engines, roller-cam versions, throttle-body injection engines, and late truck applications don’t all tell the same story. A 1969 two-barrel 318, a late-1970s emissions 318, a police 318, and a late LA truck engine can share displacement and still behave very differently. Carburetion, heads, camshaft, compression, ignition system, emissions hardware, year, and application decide what’s actually there. Same 318 badge doesn’t prove the package.

The biggest source of confusion is the Poly 318 and LA 318 split. The old A/Poly 318 and the LA 318 share displacement and family history, but they’re not the same engine. Poly heads, intakes, valve covers, and parts logic don’t turn into LA pieces because the number matches. The later Magnum 5.2L adds another wrinkle: related, but still not the same as a carbureted LA 318. Mopar kept the number alive long enough to make lazy identification expensive.

Compared with the 340, the LA 318 has less bore, less breathing room, and less factory performance intent. Compared with the 360, it has less stroke and less torque. Compared with the slant-six, it gave buyers smoother V8 power without jumping into big-block territory. None of that makes the 318 a loser. It just tells you what job it was built to do. The 318 was the normal answer, and normal answers are usually the ones that keep the bills from getting stupid.

The Mopar LA 318’s real place is as the durable, practical, long-running wedge-head small-block that carried Chrysler through decades of ordinary V8 work. It isn’t glamorous, and it doesn’t need to be. Expect it to act like a 340 because the valve covers fit, or dismiss it as scrap because it came with a two-barrel, and the little workhorse will sit there quietly while you prove you brought the wrong expectations to the right engine.

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What makes it different

The Mopar LA 318 is the small-block that survived long enough for everybody to underestimate it. The trouble starts when people read the 318 badge and drag in every nearby Mopar small-block story at once: Poly history, 273 origin talk, 340 performance envy, and 360 torque bragging. This engine has a plainer job than all that. It’s the ordinary LA workhorse, and ordinary is exactly why it spent decades doing the jobs flashier engines only bragged about.

Compared with the A/Poly 318, the LA 318 is the cleaner wedge-head replacement, not the same engine with tidier valve covers. Same bore and stroke can fool the lazy, but the heads, intake, top-end layout, accessory details, and parts logic changed. The Poly has its own old-family charm and its own ways to make parts shopping irritating. The LA 318 became the familiar small-block Mopar workhorse with better later parts support and a much bigger trail through cars, trucks, vans, and junkyards. Same cubes doesn’t mean same hardware.

Compared with the 273, the 318 is what happened when the LA family got enough displacement to become the everyday answer. The 273 started the line and deserves that respect. It’s small, crisp, and right in early LA applications. But the 318 brought more bore, more torque cushion, more general usefulness, and a lot less explaining. The 273 is the first act. The 318 is the one that kept showing up for work until nobody even looked surprised anymore.

Compared with the 340, the 318 is the engine people love to insult because it didn’t get the factory performance crown. Fine. The 340 had the bigger bore, better breathing room, stronger factory performance hardware, and the reputation. Nobody honest needs to pretend a stock 318 is a 340 with humility issues. But that doesn’t make the 318 trash. It means the 318 needs a different kind of plan: compression, cam, heads, exhaust, gearing, and realistic expectations instead of trying to win a badge fight it wasn’t built to win.

Compared with the 360, the 318 gives up stroke and easy torque. The 360 has more cubes, more low-speed shove, and a better argument when the car is heavy or the builder wants street torque without working so hard. But the 360 also brings its own balance, parts, and fitment details, so it isn’t just “better 318” with a bigger number. The 318 is smaller, smoother, common, and forgiving when used honestly. The 360 is the bigger wrench. The 318 is the one that keeps getting the job done while people complain it isn’t glamorous enough.

Compared with Magnum-era small blocks, the LA 318 belongs to the older carbureted / early electronic world before the Magnum heads, oiling details, and later roller-cam/truck logic changed the conversation. Magnum 5.2 engines share displacement and family blood, but they’re not the same parts pile. Heads, valvetrain oiling, intakes, accessories, and electronics can all get involved. If somebody says “318 is 318” and starts mixing LA and Magnum parts without checking, the engine isn’t confused. The parts order is.

The LA 318 makes sense when the job is a driver, cruiser, budget build, truck, van, mild street car, or original small-block Mopar that needs honest service instead of ego. It makes less sense when someone wants easy big power, 340 bragging rights, or 360 torque without giving the 318 the compression, airflow, cam, and gear it needs. A 318 can run well. It can even surprise people. But it won’t fix a lazy combination just because the builder read one forum story about a miracle junkyard motor.

That’s the 318’s place. It’s the LA family workhorse: more useful than the 273 for everyday torque, less special than the 340, less torquey than the 360, and not the same thing as the old Poly or later Magnum just because the number stayed alive. Build it honestly, match the parts, and stop expecting it to apologize for being common. The 318 didn’t win by being glamorous. It won by staying useful after the bragging stopped.

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General Specs

Displacement	318 cu in / 5.2L	Bore / Stroke	3.910 in × 3.3125 in
Production / Use Era	1968–1991 LA 318 regular U.S. passenger-car and light-truck 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 in LA small-block baseline
Cylinder Head Material	Cast iron	Main Journal	2.500 in
Factory Rating / Strength Lane	Mild-to-medium-duty workhorse lane; common factory versions range from low-compression 2-barrel cruiser output to stronger police, fleet, 4-barrel, roller-cam, and TBI-era truck use	Compression Ratio	Early, emissions-era, police/fleet, truck, roller-cam, and TBI versions used different compression setups; verify exact year and application
Fuel / Induction	Gasoline; carbureted or throttle-body EFI by year and application	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 for traditional LA 318 use
Weight	~500–550 lb complete iron LA small-block with typical accessories	Dimensions	~28H / ~26W / ~29L
Primary Identity Check	LA 318 wedge-head small-block; verify against A/Poly 318, Magnum 5.2, truck, police, roller-cam, and TBI-era claims	Common Use	Passenger cars, trucks, vans, fleet service, police/fleet packages, mild street cars, and budget Mopar drivers

Verify the block, bore, crank, heads, intake pattern, cam type, compression, fuel system, front dress, oil pan, converter or flywheel fit, balance hardware, stampings, and vehicle application before ordering parts. The LA 318 is common enough to make people lazy, and that’s exactly how the wrong Poly, Magnum, truck, or 360-based parts start walking into the garage.

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Variants

The LA 318 needs a variant section with guardrails because everybody thinks he knows this engine. That’s how the trouble starts. The 318 was everywhere, but a 1968 passenger-car 2-barrel, a late smog-era cruiser engine, a police 4-barrel package, a truck roller-cam core, and a Magnum 5.2 aren’t the same animal just because the displacement badge stayed friendly.

The useful split is simple: standard passenger-car LA 318s, factory 4-barrel / police / special-duty versions, emissions-era low-compression engines, truck / van / roller-cam engines, Magnum 5.2 confusion, and service / swap identity problems. That’s enough. Don’t turn the 318 into a code swamp just because Chrysler kept finding new places to bolt one.

Standard Passenger-Car LA 318

The standard LA 318 became Chrysler’s bread-and-butter small-block because it did normal work without drama. It replaced the old A/Poly 318 in regular U.S. use with a lighter, narrower, wedge-head package using the familiar 3.910-inch bore and 3.3125-inch stroke. Same cubes as the Poly. Different heads, intake, valve covers, packaging, and parts logic. The Geezer says that before the parts counter starts humming funeral music.

In ordinary passenger-car form, the 318 was usually mild: 2-barrel carburetion, hydraulic lifters, conservative cam timing, reasonable manners, and enough torque to move Darts, Satellites, Coronets, Furys, wagons, and daily drivers without acting like every stoplight was a qualifying round. That was the job, and the engine did it well.

A standard 318 isn’t junk because it came with a 2-barrel. It can be a reliable cruiser engine, a correct restoration engine, a mild street foundation, or a good swap when the goal is manners instead of bragging rights. It just isn’t a 340 wearing modest shoes, and it won’t become one because somebody adds chrome valve covers and a carburetor too big for its own manners.

The standard version needs honest expectations. Small-port heads, low compression on many later engines, mild cam timing, restrictive exhaust, and lazy gearing can make a 318 feel plain because plain was often the factory assignment. Build around the actual engine, not the number on the air cleaner.

Factory 4-Barrel, Police, and Special-Duty 318s

The 318 did have stronger factory versions, and those deserve their own lane. Police, fleet, special-duty, and factory 4-barrel versions can bring better induction, exhaust, cooling, calibration, or supporting hardware depending on year and application. That makes them more interesting than a sleepy 2-barrel cruiser engine. It doesn’t make every 318 a performance package.

A real factory 4-barrel or police 318 claim has to prove itself. Intake, carburetor, heads, exhaust, distributor, cooling package, engine stamping, application, drivetrain context, fender tag, broadcast sheet, and paperwork all matter when the seller starts adding money for the story.

A normal 318 with an aftermarket intake and a tired 4-barrel is a modified 318. It may run fine. It may be worth owning. It doesn’t become a police engine, special-duty engine, or factory high-output package because the seller learned the word “pursuit” and stood up straighter.

These stronger 318s should be respected for what they are: better factory workhorse versions with useful hardware. They’re not disguised 340s, and they don’t need that lie to matter.

Emissions-Era 318s

The emissions-era 318 is where the engine’s boring reputation got welded to the fender. Lower compression, mild cams, small-port heads, lean calibration, emissions equipment, and restrictive exhaust made many 1970s and early 1980s 318s feel about as exciting as wet cardboard with a timing light.

That doesn’t make them bad engines. It means they were built for a different fight: fuel quality, emissions rules, drivability, durability, and ordinary transportation during an era that treated performance like a public nuisance. A low-compression 318 can still be a good cruiser or budget foundation if the plan respects what’s inside.

The mistake is bolt-on fantasy. A big cam, huge carburetor, stock converter, lazy gears, weak compression, and tight exhaust won’t wake up a smog 318. They’ll make it idle like trouble and pull like regret. Cylinder pressure, airflow, exhaust, ignition curve, and gearing have to agree before the engine gets blamed.

Used correctly, an emissions-era 318 can be smooth, cheap to maintain, durable, and pleasant. Used stupidly, it becomes the reason people say 318s are weak when the real problem is the parts combination wearing a clown nose.

Truck, Van, and Roller-Cam 318s

Truck and van 318s earned the engine’s workhorse reputation the hard way. They hauled weight, idled hot, survived neglect, pulled trailers, sat in traffic, and kept running in vehicles whose maintenance history often reads like a confession nobody signed.

Depending on year, truck and van engines can bring different oil pans, mounts, exhaust manifolds, accessory drives, emissions equipment, cooling pieces, carburetion or throttle-body injection, and camshaft details. Later roller-cam LA 318s can be attractive starting points because the roller hardware can help a mild build. That still doesn’t make every truck core a prize.

A truck 318 may be a good engine. It may also be worn out, heat-soaked, overworked, sludged, mismatched, or rebuilt with whatever parts were cheapest when the fleet budget ran out. Check the actual block, heads, cam type, front dress, oil pan, exhaust, fuel system, and wear before calling it an upgrade.

The truck and van lane is useful when the buyer understands it. Don’t pay performance money for work-duty scars, and don’t dismiss a good core just because it came from something with a ladder rack and questionable wiring.

Magnum 5.2 Confusion

The Magnum 5.2 is the later descendant that keeps wandering into LA 318 conversations like a cousin who changed his name and brought different luggage. Same displacement, related family, different details. That’s the part people skip right before the intake bolts start disagreeing.

Magnum 5.2 engines use different heads, intake pattern, valvetrain oiling, rocker gear, valve covers, fuel injection, accessory layout, and engine-management logic compared with a traditional carbureted LA 318. Some ideas cross. Some parts adapt. Some parts make a simple job turn into a pile of small corrections.

A Magnum 5.2 can be a good donor. Magnum heads can be useful in the right plan. Roller-cam architecture can help. But none of that makes the Magnum just an LA 318 with fuel injection and better manners. It has its own rules.

If a seller says “318” and the engine has Magnum heads, EFI hardware, later truck accessories, or the Magnum intake pattern, identify it before buying parts. The number gets the conversation started. The bolt pattern gets the final laugh.

Service, Swap, and Identification Confusion

The LA 318 is common enough that people stop respecting the details. That’s the danger. Rare engines make buyers cautious. A 318 makes them shrug, and the shrug is where the money leaks out.

After decades of swaps, rebuilds, 4-barrel conversions, police claims, truck takeouts, roller-cam cores, Magnum parts, and half-remembered stories, a surviving 318 may not match the car, the paperwork, or the seller’s memory. It may be a correct original. It may be a good replacement. It may be a worn-out core wearing one color of paint and three generations of excuses.

The proof burden depends on the claim. A basic driver needs correct identification and a health check. A factory 4-barrel, police, special-duty, original-engine, roller-cam, truck, or Magnum-swap claim needs more. Casting numbers, stampings, heads, intake pattern, carburetion or EFI, cam type, exhaust, accessories, application, tags, broadcast sheet, and paperwork all need to line up before the price gets brave.

The LA 318 is a good engine because it’s useful, durable, common, and forgiving. Forgiving doesn’t mean magical. If the parts don’t match the job, it’ll still run badly, pull weakly, and drain the wallet while the owner blames Chrysler instead of the combination.

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Key Points

The LA 318 is Chrysler’s everyday LA small-block workhorse. Its value isn’t mystery, rarity, or badge drama. Its value is usefulness: it fits, starts, idles, pulls ordinary cars and trucks, accepts mild upgrades, and keeps old Mopars moving without demanding 340 money every time the hood opens.

The basic fingerprint is 318 cubic inches from a 3.910-inch bore and 3.3125-inch stroke. That bore gives it more breathing room than the 273, but less performance ceiling than the 340. The stroke keeps it shorter than the 360’s torque-heavy layout. That puts the LA 318 in the practical middle: enough engine for real street use, not enough engine to rescue a bad combination by brute force.

The most important identity split is simple: LA 318, A/Poly 318, and Magnum 5.2 are separate parts conversations. The old Poly 318 uses wide polyspherical-head hardware. The LA 318 uses wedge-head LA hardware. The Magnum 5.2 is the later truck-era descendant with different heads, intake pattern, valvetrain oiling, valve covers, and fuel-system logic. The shared number starts the conversation. It doesn’t order the parts.

The LA 318 became common because it solved normal problems. It worked in passenger cars, trucks, vans, fleet rigs, police packages, daily drivers, and mild street builds. That broad use is why condition and application matter so much. A clean passenger-car core, a tired emissions-era engine, a hard-worked truck motor, a police-package claim, and a later roller-cam takeout can all wear the same displacement label while telling very different stories.

A stock or near-stock LA 318 should be judged as a workhorse, not as a failed performance engine. Many factory versions were mild by design: small-port heads, two-barrel carburetion, conservative cam timing, low or moderate compression, and quiet exhaust. That was not stupidity. It was the recipe for drivability, warranty survival, and owners who wanted the car to start on Monday instead of winning a parking-lot argument on Saturday.

The 318 responds well when the parts match the mission. A sensible cam, decent compression, clean ignition curve, properly sized four-barrel, matched intake, real exhaust, healthy cooling, and reasonable gearing can make a 318 feel much sharper without ruining manners. The engine rewards clean combination work. It punishes catalog bravery, especially when compression and gearing are already asleep.

The common mistake is building the 318 like a bigger engine with smaller numbers. Big cams, oversized carburetors, large-port heads, lazy gears, weak cylinder pressure, and heavy vehicles can make it softer than the mild engine that came out. The 318 can run well, but it needs velocity, compression, timing, and torque where the car actually drives. It isn’t a displacement charity program for parts meant for something larger.

Factory 4-barrel, police, fleet, special-duty, roller-cam, and truck claims deserve proof. A four-barrel intake, orange paint, chrome valve covers, headers, or a “mild cam” story may describe a useful modified engine. They don’t prove a factory package. If the claim adds money, the intake, carburetor, heads, exhaust, distributor, cooling pieces, stampings, application, tags, paperwork, and drivetrain context need to agree.

Parts support is strong, but the 318 still needs year-aware checking. Early and later LA details, flat-tappet versus roller-cam hardware, carburetor versus TBI fuel systems, car versus truck front dress, oil pan shape, kickdown linkage, accessory brackets, ignition pieces, converter or flywheel fit, and emissions hardware can all change the order. “LA small block” gets the buyer into the right neighborhood. It doesn’t hand over the right house key.

Interchange needs discipline because the LA 318 sits close to too many tempting donors. Some 273, 340, 360, and Magnum parts can help when the whole combination supports them. Some parts fit but hurt compression, airflow speed, oiling, balance, accessory alignment, or street manners. The 360’s external-balance hardware doesn’t belong on a normal internally balanced 318, and Magnum top-end parts bring their own oiling and intake rules.

A used LA 318 core still needs real inspection. Check for cracks, freeze damage, stuck cylinders, ridge wear, bad crank journals, worn cam lobes, tired timing sets, lifter-bore wear, deck damage, oiling abuse, sludge, broken exhaust bolts, missing brackets, hacked wiring, wrong oil pan, mixed-year accessories, and previous rebuild work done by somebody who treated silicone like structural steel.

The LA 318’s value depends on purpose. A complete, healthy, known-application engine with the right brackets, pulleys, manifolds, linkage, oil pan, front dress, and drivetrain pieces can be a great score. A stripped long block with unknown internals and a pile of missing hardware can still be a bad deal, even if every Mopar guy within earshot says “318s run forever.”

The LA 318 belongs in the honest-driver lane first. It is a smart choice for reliability, mild street manners, stock-style restoration, trucks, vans, budget builds, and old Mopars that need to run more than they need to brag. If the goal is serious horsepower, easy torque, or factory performance value, the 340, 360, Magnum, or stroker conversation should start before the wallet gets heroic.

That’s the real lesson: the LA 318 isn’t junk, and it isn’t magic. It is a durable, common, useful small-block that does best when the plan respects its bore, compression, airflow, gearing, and job. Build it honestly and it will earn its keep. Build it like a discount 340 or tiny 360 and it will make the owner pay for the fantasy.

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Common Problems

The 318 LA’s trouble starts because it’s too familiar for its own good. Everybody has heard of one. Everybody has owned one, pulled one, ignored one, or seen one sitting in a truck. That reputation is useful, but it also makes people sloppy. The LA 318 isn’t the earlier poly 318, not a 340 with smaller stickers, and not a 360 just waiting for bigger heads and optimism.

• A/Poly 318 Confusion
  The LA 318 isn’t the earlier A/Poly 318. Same displacement number. Different engine. Different heads, intake layout, valve covers, width, look, and parts reality.
  
  That confusion still burns buyers and parts counters. Intake manifolds, valve covers, exhaust, brackets, front dress, mounts, and identification clues need checking before anyone orders parts by displacement alone. “It’s a 318” is only half a sentence. The expensive half comes after the family name.
• Two-Barrel Workhorse Misread
  Most LA 318s lived honest two-barrel workhorse lives. That isn’t an insult. It’s the reason so many survived. The problem starts when people either dismiss every 318 as grocery-store furniture or pretend every clean one is hiding a factory performance package.
  
  Carburetion, intake, compression, heads, camshaft, exhaust, application, dates, and vehicle context need checking before the story gets upgraded. A plain two-barrel 318 can be a good engine. It doesn’t become a high-performance small-block because somebody found a four-barrel intake and started talking faster.
• 340 / 360 Parts Expectations
  The 318 belongs to the LA family, but it’s not a 340 or 360 with a smaller number on the air cleaner. The bore, compression, heads, cam choice, and intended use change the build plan.
  
  Big-port heads, big camshafts, oversized carburetion, lazy gearing, and heavy vehicles can make a 318 worse instead of better. Some 340/360-style parts can work in the right combination. Some just move the powerband to a place the 318 never wanted to live. The catalog doesn’t know what the car weighs.
• Low Compression and Smog-Era Reality
  Later LA 318s can be tough, cheap, and easy to find, but many came from the low-compression, emissions-era world. That matters when somebody expects bolt-on miracles.
  
  Compression ratio, piston depth, camshaft choice, head chamber size, ignition curve, carburetion, exhaust, and gearing all need to work together. A tired low-compression 318 with a big cam isn’t a sleeper. It’s a lesson in how to make less torque with more noise.
• Magnum 318 Confusion
  The Magnum 5.2 carried the 318 displacement forward, and that creates another round of sloppy assumptions. LA and Magnum engines are related, but they aren’t the same parts pile.
  
  Heads, intake bolt pattern, rocker gear, valvetrain oiling, timing cover details, accessory drive, fuel system, and engine-management pieces can change the job fast. A Magnum swap or parts mix can be smart. Calling every 5.2 “just a 318” is how the project starts ordering parts from two different engine generations and trusting both boxes.

For broader Mopar LA-series problems shared across the engine family, use the Mopar LA-series family page under Common Family Problems.

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Common Misconceptions

The 318 LA gets misunderstood because it’s common, durable, and easy to underestimate. That combination makes people say dumb things from both directions. One crowd calls it junk because it’s not a 340. The other crowd thinks it becomes a 340 with a cam, carb, and enough garage confidence. The 318 is better than the haters say and less magical than the dreamers want.

• “The LA 318 is the same as the poly 318.”
  No. Same displacement, different engine family. The A/Poly 318 and LA 318 don’t share the same heads, intake layout, valve covers, appearance, or parts assumptions.
  
  The LA 318 needs LA identification and LA parts checking. The poly 318 needs A/Poly checking. Mixing the two by name is how the wrong intake arrives looking proud of itself.
• “All LA 318s are weak smog engines.”
  No. Some later 318s were low-compression, emissions-era workhorses. That doesn’t make every LA 318 weak, useless, or unbuildable.
  
  A healthy 318 with the right compression, cam, heads, intake, exhaust, ignition, and gearing can be a good street engine. It just needs a matched plan, not a pile of parts chosen by somebody angry at displacement.
• “A 318 can be built just like a 340.”
  No. The 340 has more bore, better breathing room, more factory performance identity, and a different build argument. The 318 can run well, but it doesn’t become a 340 because the camshaft got ambitious.
  
  A good 318 build needs parts sized for the engine. Too much cam, too much carburetor, too much head, and not enough compression can turn a dependable small-block into a loud disappointment.
• “Any 360 part is an upgrade for a 318.”
  No. Some 360 parts can help in the right build. Some can hurt. Bigger doesn’t automatically mean better.
  
  Heads, intake, camshaft, carburetion, exhaust, compression, gearing, and intended use all need to match. A 318 doesn’t care that the part came from a bigger engine. It cares whether the combination works.
• “The 318 is worthless because 340s and 360s exist.”
  Wrong. The 340 and 360 have real advantages, but the 318 has its own job. It’s common, durable, affordable, and useful in drivers, trucks, swaps, budget builds, and mild street cars.
  
  The 318 isn’t the glamour engine. Fine. Glamour doesn’t get the car to work, pull the parts hauler, or run for years while the expensive project sits on jack stands.

For broader Mopar LA-series misconceptions shared across the family, use the Mopar LA-series family page under Common Family Misconceptions.

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Upgrade Limitations

The Mopar LA 318 is the engine everybody thinks they understand because there are so many of them. That’s how it gets underrated, overbuilt, and abused all at once. It’s not the earlier 318 Poly, a discount 340, a polite 360, or automatically a Magnum 5.2 just because the displacement stayed familiar. The LA 318 is a durable, useful small-block, but it still has limits that cubic-inch daydreaming won’t fix.

The LA 318 uses a 3.91-inch bore and 3.31-inch stroke. That gives it the same basic bore and stroke size as the old 318 poly, but the LA architecture, heads, intake, valvetrain layout, front dress, emissions-era details, and later parts world are different. The 318 LA has much better support than the early poly engines, but support isn’t the same as permission to bolt on every 340, 360, or Magnum part and expect the engine to smile.

The first upgrade limitation is displacement. The 318 can make a strong, pleasant street engine, but it doesn’t have the bore and cubic inches of a 340 or 360. Big-port heads, too much carburetor, too much cam, lazy compression, tall gearing, weak exhaust, and a heavy vehicle can make it feel soft. The 318 rewards matched parts. It punishes catalog bravery.

Compression is where many LA 318 builds go flat. A lot of later 318s lived through emissions-era compression, mild cams, small ports, conservative carburetion, and heavy vehicles. Tossing a big cam and shiny intake on one of those engines without fixing compression and airflow usually makes noise, not power. A 318 needs cylinder pressure, quench where practical, correct cam timing, and a realistic fuel plan before it gets asked to act like a larger engine.

Camshaft choice needs restraint. The 318 can wake up nicely with a sensible cam, good tune, better exhaust, and a four-barrel when the rest of the combination supports it. It can also become a lazy mess with too much duration and not enough compression, converter, or gear. A street 318 wants throttle response, vacuum, usable torque, and manners. It doesn’t need a cam selected by someone trying to impress a parking lot.

Cylinder heads need to match the engine’s size. Better heads can help, especially when the compression, cam, intake, and exhaust agree. But large-port heads intended for bigger small-blocks can make a mild 318 sluggish if the rest of the build isn’t ready. Valve size, chamber volume, port volume, piston height, gasket thickness, and compression ratio all matter. A 318 doesn’t need the biggest head in the room. It needs the right head.

Induction is another place people overspend in the wrong direction. A two-barrel 318 can be a perfectly good cruiser. A four-barrel can be a strong upgrade with the right intake, carb size, ignition curve, exhaust, and gearing. Too much carburetor, a mismatched intake, poor linkage, bad fuel distribution, or a tall single-plane on a mild engine can make it worse. The 318 doesn’t need carburetor theater. It needs clean mixture and response.

The 318 also gets caught between LA and Magnum assumptions. Later Magnum 5.2 engines share the 318 displacement, but heads, intake pattern, oiling through the valvetrain, rocker system, front dress, accessory layout, and electronics-era details differ. Magnum head swaps and later parts can work in the right plan, but they aren’t casual bolt-on magic. If the build mixes LA and Magnum pieces, oiling, pushrods, intake fit, rocker gear, compression, and accessory details need real checking.

Roller-cam, flat-tappet, emissions-era, truck, van, police, and service-engine details also need exact-year checking. A later LA 318 may not use the same cam, lifters, timing parts, heads, ignition, accessory brackets, oil pan, or emissions hardware as an earlier one. “318 LA” is a good starting label. It’s not a complete parts order.

Core condition still matters. The LA 318 is tough, but it isn’t immortal. Worn bores, tired rings, worn heads, cracked exhaust manifolds, damaged threads, worn timing sets, wiped cam lobes, sludge, bad oiling history, corroded cooling passages, missing brackets, and mixed-year hardware can turn a cheap engine into an expensive lesson. The 318’s reputation for durability doesn’t rebuild the thing for free.

The honest upgrade plan is mild to moderate and matched. Build the LA 318 when you want reliability, street manners, decent torque, easy parts, and a small-block Mopar that can live in the real world. Use compression that matches the fuel, a cam that fits the car, heads that fit the displacement, a sensible intake and carburetor, good ignition, real exhaust, and gearing that helps. If the goal is serious horsepower per dollar, a 340, 360, or stroker plan usually starts ahead. The 318 is good. It just doesn’t deserve to be bullied into pretending it’s bigger.

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When It Actually Makes Sense

The LA 318 makes sense when the goal is a reliable small-block Mopar driver. It starts easily, runs smoothly, takes normal use well, and has enough parts support to be kept alive without turning every repair into an archaeological dig. In a cruiser, truck, daily-style classic, mild street car, or budget Mopar build, that matters.

It makes sense when the engine already belongs in the car. A correct 318-equipped Dodge, Plymouth, Chrysler, truck, van, or proper factory application can be better served by a healthy matched 318 than by a half-planned swap. Originality may not always make the car more valuable, but keeping a good engine that fits, cools, shifts, and drives properly isn’t a dumb plan.

It also makes sense when the build stays realistic. A mild cam, four-barrel, dual exhaust, better ignition curve, proper compression, and good tune can make a 318 feel much better without ruining manners. The engine responds well when the parts are chosen for low- and mid-range use instead of imaginary race duty.

The 318 makes sense where fuel economy, drivability, and durability matter more than bragging rights. It’s not the biggest LA engine, and that’s part of why it can be pleasant. A properly built 318 can be smooth, dependable, and easy to live with while still giving an old Mopar enough V8 feel to be worth driving.

It makes less sense when the goal is big power on a tight budget. By the time you buy pistons, heads, cam, intake, carburetor, machine work, exhaust, converter, gears, and tuning to make a 318 chase larger-engine numbers, a 360 or stroker foundation may have been smarter. That doesn’t make the 318 bad. It means the horsepower goal has to respect the starting point.

It also makes less sense when the engine is a worn-out smog-era core and the owner expects bolt-ons to fix everything. If compression is low, the cam is tired, the timing set is loose, the heads are weak, and the tune is sloppy, a shiny intake won’t rescue it. The engine needs health before decoration.

Plain answer: build the LA 318 when you want a reliable, sensible, street-friendly Mopar small-block with good parts support and honest manners. Don’t build it because you think it’s a cheap 340 or 360 in disguise. It isn’t. The 318 is happiest when the plan stops asking it to lie.

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Compatibility Notes

Family identity.
The 318 LA is a Mopar LA-series small-block V8. It’s not the earlier A-series 318 Poly, a Magnum 5.2, a 340, or a 360. It belongs to the LA family, but exact year, application, heads, intake, front dress, crank, balance, and transmission details still decide what fits.

Bore and stroke proof.
Verify the actual engine before trusting the badge. The LA 318 uses a 3.91-inch bore and 3.31-inch stroke. Check casting numbers, stampings, bore, crank, pistons, heads, intake, date context, vehicle application, and physical measurements before calling it an LA 318, poly 318, Magnum 5.2, 340, 360, truck engine, police engine, roller-cam engine, or swap mystery.

318 LA versus 318 poly.
The LA 318 and the earlier 318 poly share displacement, not top-end identity. Blocks, heads, intakes, valve covers, valvetrain layout, exhaust fit, and many accessory relationships differ. Don’t order poly parts for an LA or LA parts for a poly because both say 318. That mistake has been expensive since the parts counter learned to sigh.

318 LA versus Magnum 5.2.
The Magnum 5.2 is a later 318-family engine, but it’s not the same as a traditional LA 318. Cylinder heads, intake bolt pattern, rocker oiling, pushrods, valve covers, front dress, accessory layout, fuel injection pieces, and electronics-era hardware can differ. Magnum swaps and Magnum head conversions can work, but oiling, intake fit, pushrod length, compression, and accessory details need proof.

318 LA versus 340.
The 340 is a larger-bore performance LA engine with different expectations. It can use different heads, pistons, compression, camshaft, intake, exhaust, and value logic. A 340-style build plan can be too much for a mild 318. The 318 can be improved, but it doesn’t become a 340 because the valve covers got confident.

318 LA versus 360.
The 360 is a larger-displacement LA engine with a different stroke, larger main journals, different balance requirements, and different torque expectations. Don’t assume 360 crank, damper, converter, flexplate, flywheel, pistons, or balance parts belong on a 318. The 360’s external-balance hardware doesn’t get to wander onto a 318 just because both are LA small-blocks.

Heads, intake, and valvetrain.
Verify head casting, chamber size, valve size, intake manifold fit, rocker gear, pushrods, lifters, camshaft, timing parts, and oiling details by exact year and build plan. LA engines span enough years that “small-block Mopar” isn’t a complete parts description. Roller-cam, flat-tappet, emissions-era, truck, car, and performance-style combinations need separate checking.

Crank, balance, and transmission fit.
Verify crank register, crank flange, internal balance, damper, converter, flexplate, flywheel, starter location, bellhousing or case pattern, clutch parts, linkage, mounts, driveshaft, and rear gear by exact year and application. Most LA 318s are internally balanced, but swap parts still need checking. The 360’s external-balance hardware doesn’t belong on a 318 unless the whole rotating assembly has been deliberately engineered that way.

Front dress, cooling, and accessories.
Check timing cover, water pump outlet side, pulleys, alternator brackets, power steering brackets, A/C brackets, radiator hose routing, fan spacing, oil pan, mounts, and chassis clearance. Early and later LA front-dress parts can differ, especially when mixing car, truck, van, and later accessory systems. The front of the engine is where “same family” often starts leaking.

Car, truck, van, police, and emissions differences.
A 318 may come from passenger-car, truck, van, police, emissions-era, roller-cam, flat-tappet, or later service use. Those engines can carry different oil pans, mounts, brackets, heads, camshaft, carburetion, ignition, exhaust, front dress, accessory layouts, and emissions hardware. Don’t assume a truck 318 drops into a car like it showed up wearing the right shoes.

Restoration-correct versus driver-correct versus performance-correct.
For restoration-correct work, the right 318 and supporting hardware can define the car. For a driver, a mild matched build can be reliable, smooth, and satisfying. For performance work, be honest about the goal. The LA 318 can be a great small-block, but it isn’t a 340, it isn’t a 360, and it isn’t obligated to make bad parts choices look smart.

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Reality Check

The LA 318 is better than the haters say and less magical than the dreamers want. That’s the whole engine in one greasy sentence. It’s common, durable, useful, and cheap enough to be taken for granted, which is exactly why people either throw it away too fast or overbuild it into disappointment.

A good 318 can be a fine driver engine. With decent compression, sensible cam timing, clean ignition, a matched intake and carburetor, good exhaust, and gearing that fits the car, it can make an old Mopar pleasant, dependable, and more fun than the bench racers admit. It doesn’t need to become a 340 to be worth owning.

But the limits are real. The 318 doesn’t have the 340’s bore and breathing room or the 360’s stroke and torque. Low-compression smog-era versions need health and combination work before bolt-ons do much. Big cams, oversized carburetors, lazy gears, and weak cylinder pressure turn the 318 into a noisy lesson, not a sleeper.

The identity details matter too. LA 318, A/Poly 318, and Magnum 5.2 aren’t the same parts pile. Car, truck, van, police, roller-cam, emissions-era, and service engines can also carry different hardware. The engine may be common, but the wrong parts still don’t bolt on out of respect.

The hard truth is simple: build the 318 when you want a reliable, sensible, street-friendly Mopar small block. Choose a 340, 360, Magnum, or stroker plan when the power goal needs more engine. The 318 is a workhorse. Treat it like one and it’ll earn its keep. Treat it like a cheap disguise for a bigger engine and it’ll make you pay for the lie.

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Bottom Line

The Mopar LA 318 is Chrysler’s practical small-block workhorse. It wasn’t built to be the glamour engine, and that’s exactly why it survived everywhere. Passenger cars, trucks, vans, police packages, fleet rigs, cruisers, and budget builds all used the 318 because it was simple, durable, and useful. That kind of boring deserves more respect than it usually gets.

The 318 makes the most sense when the job is reliability, drivability, and mild street use. A healthy 318 with the right compression, camshaft, ignition, induction, exhaust, cooling, converter or clutch, and gearing can be a smooth, enjoyable engine. It may not win a cubic-inch argument, but it can make a Mopar run right without turning the project into a wallet bonfire.

It makes less sense when the goal is serious horsepower per dollar. By the time a builder buys pistons, heads, cam, intake, carburetor or EFI pieces, machine work, exhaust, converter, gears, and tuning to make a 318 chase bigger-engine numbers, a 340, 360, Magnum, or stroker foundation may already be the smarter move. That doesn’t make the 318 bad. It means the goal has to fit the starting point.

The mistake to avoid is assuming every 318 is the same. The A/Poly 318, LA 318, and Magnum 5.2 all need separate identification. Passenger-car, truck, van, police, emissions-era, roller-cam, and service engines can also carry different parts. Casting numbers, stampings, heads, intake pattern, fuel system, cam type, front dress, oil pan, balance parts, and application all need to support the plan.

Condition and completeness matter more than the famous “318 runs forever” line. A complete, healthy engine with the right brackets, pulleys, manifolds, oil pan, linkage, and known history can be a great score. A tired, low-compression, half-stripped core with mixed-year parts can become expensive before it becomes useful. Common doesn’t mean free to rebuild.

Bottom line: the LA 318 is a good engine when it’s treated honestly. Build it for street manners, reliability, and useful torque, and it’ll do the job without whining. Don’t confuse it with a Poly, don’t call every 5.2 a plain LA, don’t expect 340 breathing or 360 torque, and don’t let a cheap core talk you into an expensive fantasy.

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