Mopar 318 Engine Specs

Intro

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

The Mopar LA 318 is the engine that did the boring work so well people eventually started confusing boring with bad. Introduced in volume for 1968, it took the familiar 318-cubic-inch number from the old Poly era and attached it to Chrysler’s newer, lighter, narrower wedge-head LA architecture. Same displacement. Different engine. Chrysler reused the number because it made perfect sense at the time and guaranteed parts-counter arguments for the next fifty years.

The 318 became the center of the LA family because it was large enough to do useful work without demanding much in return. Its 3.910-inch bore and 3.3125-inch stroke gave it more displacement than the little 273 while keeping the short-stroke bottom-end proportions later shared with the 340. It was not built around maximum airflow, heroic rpm, or showroom intimidation. It was built around starting every morning and getting the car home again.

Chrysler put the thing everywhere. Darts, Satellites, Coronets, Furys, wagons, trucks, vans, police cars, fleet vehicles, and enough anonymous daily drivers to wear out several generations of upholstery all got 318 power. Most versions used mild compression, a two-barrel carburetor, hydraulic lifters, conservative cam timing, and exhaust designed more around silence than enthusiasm. That was not Chrysler accidentally forgetting to build a 340. Normal people needed engines too.

The reputation for durability came from surviving exactly that kind of normal service, plus plenty that was not normal at all. Neglected oil changes, overheated vans, tow duty, cold starts, bargain ignition parts, clogged carburetors, fleet maintenance, teenagers, and previous owners with theories all took their turns. Plenty of 318s eventually wore out. The impressive part is how much nonsense many of them tolerated before finally doing it.

There were stronger factory versions. Four-barrel, police, fleet, special-duty, later roller-cam, and truck combinations can bring better induction, calibration, cooling, camshaft, or supporting hardware depending on year. They deserve to be identified correctly without turning every 318 wearing an aftermarket four-barrel into a pursuit engine somebody’s uncle supposedly outran the law with.

The emissions years did the engine’s reputation no favors. Low compression, mild cams, restrictive exhaust, lean mixtures, and tall gearing could make a perfectly healthy 318 feel as though somebody had placed a pillow over the carburetor. Blaming the basic engine for that is like blaming the mule because somebody loaded the wagon with concrete.

The 318 responds well to sensible improvements because it starts with decent architecture and enough displacement to use them. Reasonable compression, a camshaft sized for the actual car, a properly sized four-barrel, better exhaust, good ignition, and gearing that is not asleep can wake one up considerably. The trick is stopping before every part in the catalog gets selected because the word “performance” appeared in bold type.

That is where 318 builds usually go wrong. Large-port heads, too much camshaft, too much carburetor, weak compression, stock converter, tall rear gears, and a heavy car can turn a cheap engine into an expensive device for producing noise. A 318 likes airflow velocity, cylinder pressure, and parts that agree with one another. Cubic inches cannot rescue a combination assembled by enthusiasm alone.

For a dependable cruiser, stock-style restoration, truck, van, or mild street Mopar, a healthy LA 318 remains one of the easiest Chrysler V8s to defend. For serious horsepower, the arithmetic eventually starts favoring a 340, 360, Magnum, or stroker foundation. Knowing when to stop spending money on the smaller engine is not surrender. It is evidence that somebody in the garage owns a calculator.

↑ Back to the Top, Before the Casting Numbers Start Lying

---

Overview

The LA 318 became Chrysler’s default small-block answer because it occupied the useful middle of the family. The 273 had established the LA architecture, but 273 cubic inches were better suited to light cars than to everything Chrysler intended to power. The 340 would later chase performance and the 360 would add torque. The 318 got assigned nearly everything else.

Its dimensions were 3.910-inch bore by 3.3125-inch stroke for 318 cubic inches. The block retained the LA family’s 4.460-inch bore spacing, roughly 9.600-inch deck height, five main bearings, in-block camshaft, pushrods, wedge heads, shaft-mounted rocker arms, and rear distributor. Traditional LA 318 rotating assemblies were internally balanced, with 2.500-inch main journals and 2.125-inch rod journals.

Those bore-and-stroke dimensions happen to be essentially the same as the earlier A-series Poly 318, which is historically neat and mechanically responsible for more confusion than neatness ought to be allowed to cause. The LA engine uses a completely different top-end arrangement: wedge heads rather than polyspherical heads, narrower packaging, different intake and exhaust pieces, different valve covers, and its own valvetrain and accessory logic.

So the first rule with any “318 Mopar” is determining which 318 somebody means. The Poly came first. The LA carried the number through decades of production. The later Magnum 5.2 kept the displacement alive again with another round of changes. Chrysler got excellent mileage out of 318 cubic inches and apparently felt restorers could sort out the consequences themselves.

In regular passenger-car use, the LA 318 was usually deliberately mild. Two-barrel carburetion, hydraulic lifters, conservative camshaft timing, modest compression, quiet exhaust, and street-friendly ignition calibration made it easy to start, easy to drive, and difficult to kill. Those qualities sell far more automobiles than a lumpy idle, even if nobody hangs posters of them in the garage.

That mild specification also made later owners underestimate the basic engine. A low-compression 318 with a small carburetor, restricted exhaust, tall gears, and thirty years of timing-chain stretch can feel thoroughly unimpressive. That tells you what condition and combination it is in. It does not prove 318 cubic inches are genetically opposed to acceleration.

Chrysler built stronger versions when the application called for them. Factory four-barrel, police, fleet, and special-duty combinations could receive better induction, exhaust, calibration, cooling, or other supporting equipment. These were useful upgrades built around the same basic displacement rather than secret 340s hiding inside fleet paperwork.

Police-engine stories deserve the same skepticism as every other valuable factory claim. Intake, carburetor, heads, exhaust, distributor, cooling equipment, engine stamping, application, fender tag, broadcast information, drivetrain, and documentation should support the story. A Thermo-Quad acquired at a swap meet does not confer law-enforcement service on the block beneath it.

The emissions era changed the personality more dramatically than the architecture. Compression fell. Camshaft timing got milder. Exhaust systems became more restrictive. Carburetion and ignition calibration had to satisfy emissions requirements instead of somebody’s desire to leave two black stripes behind the Dairy Queen. Many later 318s therefore earned their sluggish reputation honestly, but the cause was the factory combination rather than some sudden weakness in the block.

Those engines can still make good street foundations if the rebuild restores what the later factory package surrendered. Compression, cylinder pressure, sensible cam timing, decent heads, appropriately sized induction, free exhaust, and proper ignition can transform the way a 318 behaves. Removing emissions equipment alone does not restore compression. Pistons remain stubbornly involved in that discussion.

Truck and van service gave the 318 another long career. These applications valued durability, torque at ordinary rpm, cooling capacity, and the ability to tolerate work more than quarter-mile manners. They also left behind plenty of used engines that have spent decades hauling weight, idling hot, pulling trailers, and receiving whatever maintenance somebody remembered before Friday afternoon.

A truck or van 318 can therefore be an excellent core and still deserve suspicion. Oil pans, mounts, exhaust manifolds, brackets, front dress, cooling pieces, carburetion, throttle-body injection, and accessory arrangements can differ from passenger-car hardware. The engine may bolt to the transmission and still have half its external parts arguing with the chassis.

Later LA production added roller-cam versions, which can be attractive foundations for mild street work. Roller hardware removes some flat-tappet concerns and gives the builder another useful path. But “roller 318” still does not tell the entire story. Year, block, heads, fuel system, front dress, application, and supporting parts remain part of the purchase.

Throttle-body-injected late LA engines add another transition step before the Magnum family takes over. These engines retain LA architecture while carrying later fuel-system and electronic hardware. A builder converting one to older-style induction needs to understand what belongs to the long block and what belonged to the vehicle electronics before the wire cutters become management.

The Magnum 5.2 is where the family relationship gets close enough to encourage particularly expensive optimism. The later engine shares displacement and Chrysler small-block ancestry but uses different heads, intake attachment, pedestal rocker gear, pushrod oiling, valve covers, fuel injection, accessories, and engine-management systems.

Magnum heads and other later pieces can be useful in a planned LA build, but the word “useful” is doing important work there. Oil passage requirements, intake fit, pushrod length, compression, rocker geometry, and accessory arrangements have to be planned. Parts do not become interchangeable merely because both engines appear on the same family reunion photograph.

Compared with the 273, the 318 keeps roughly the same stroke and adds substantially more bore. That gives it more displacement, more breathing room, and considerably more usefulness in heavier vehicles while preserving the short-stroke character of the early LA branch.

Compared with the 340, the 318 gives away bore diameter and factory performance hardware. The 340’s 4.040-inch bore allows larger valves and more airflow, and Chrysler built the engine around performance from the beginning. Installing large 340-style heads on a mild 318 can work in the right combination. Installing them because “bigger must be better” can also remove the port velocity the smaller engine was using to stay awake.

Compared with the 360, the 318 uses less bore, less stroke, smaller main journals, and an internally balanced factory rotating assembly. The 360’s 3.580-inch stroke brings more displacement and torque, along with its own external-balance requirements. A weighted 360 converter, damper, or flywheel does not belong on a normal LA 318 merely because both blocks accept many of the same surrounding pieces.

That difference becomes increasingly important when a street build starts chasing power. A mild 318 can be a tremendous bargain because the core is common and the existing engine may already be complete. But once the plan includes pistons, expensive heads, substantial machine work, large induction, converter, gears, exhaust, and every other performance expense, the savings from starting with 318 cubic inches can quietly evaporate.

That does not mean every 318 should be replaced with a 360. A complete, healthy 318 already installed in the correct car can make far more sense than buying an unknown larger core and starting over. Existing brackets, pan, pulleys, linkage, accessories, exhaust, transmission pieces, and cooling hardware all have value. The cheapest engine is occasionally the one whose parts are already attached.

For a sensible street combination, the 318 rewards restraint. Useful compression, moderate cam timing, a properly sized four-barrel, good ignition advance, real dual exhaust, and gearing appropriate to the vehicle can make one responsive without sacrificing the manners that made the engine popular in the first place.

Too much camshaft is probably the most traditional way to ruin that advantage. Weak cylinder pressure combined with a large cam, stock converter, tall gears, heavy vehicle, oversized carburetor, and large-port heads can produce an engine that sounds impressive at idle and spends the rest of its time waiting for rpm that never arrives. Noise is not torque. Chrome is also not torque, though catalogs continue experimenting with the theory.

Used cores deserve the same inspection as any engine that has been alive since disco. Check cylinder wear, ridge, rust, crank journals, cam lobes, timing set, lifter bores, oiling condition, sludge, decks, exhaust bolts, cooling passages, and previous machine work. A 318 may have survived incredible neglect. That does not mean the clearances survived with it.

Completeness deserves attention because common engines can still become expensive when all the ordinary pieces are missing. Brackets, pulleys, correct oil pan, pickup, manifolds, kickdown linkage, accessory drives, ignition parts, converter or flywheel, and front dress can consume plenty of money when purchased individually. A bare cheap engine can spend itself into an expensive engine without ever making compression.

The LA 318’s strongest modern role remains the same one Chrysler gave it: dependable general-purpose service. It is excellent in a cruiser, stock-style restoration, mild street car, truck, van, or budget Mopar where smooth operation and durability count more than a horsepower number somebody can repeat at lunch.

For serious performance, know when the project has crossed into another engine’s territory. A 340 brings the desirable bore and factory performance identity. A 360 starts with more displacement and torque. Magnum and stroker combinations open other doors. Spending heavily to avoid changing the number stamped on an ordinary 318 can eventually become loyalty to the wrong part of the engine.

The 318 survived because it was neither junk nor magic. It was simply a durable, forgiving small-block built in enormous numbers for jobs that needed a V8 without requiring a parade. Build it around what 318 cubic inches actually do well and it remains one of the most useful Mopar engines ever made. Build it like a discounted 340 or undersized 360 and the dyno sheet will eventually send the parts catalog a thank-you note.

↑ Back to the Top, Before the Casting Numbers Start Lying

---

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.

↑ Back to the Top, Before the Casting Numbers Start Lying

---

Variants

The LA 318 stayed around long enough to collect plenty of different carburetors, compression ratios, cams, fuel systems, and work assignments, but the Geezer is not turning every emissions calibration into its own engine. The useful hardware map is narrower: the ordinary two-barrel passenger-car 318, stronger factory four-barrel / police / special-duty combinations, and the later truck-and-van engines that brought roller valvetrains and, in some applications, throttle-body injection. The Magnum 5.2 comes afterward and belongs to another chapter no matter how familiar the cubic inches look.

Standard Passenger-Car 318 — Two-Barrel

What it was: This was Chrysler’s bread-and-butter LA 318, the engine that spent decades hauling Darts, Satellites, Coronets, Furys, wagons, and assorted family debris without demanding applause.

What changed: The standard combination centered on two-barrel carburetion, hydraulic lifters, conservative cam timing, street-oriented heads and exhaust, and an internally balanced 3.910-inch-bore, 3.3125-inch-stroke rotating assembly.

What that did: It made the 318 smooth, durable, forgiving, and thoroughly uninterested in winning parking-lot horsepower arguments. In the later emissions years, lower compression, leaner calibration, milder cam timing, and restrictive exhaust could make the same basic engine feel considerably sleepier. That was the package getting softer, not the block suddenly forgetting how combustion worked.

Where used: Regular Chrysler, Dodge, and Plymouth passenger-car and wagon applications throughout the LA 318 era.

Factory Four-Barrel / Police / Special-Duty 318

What it was: Chrysler also built stronger 318 combinations for applications that needed more breathing, harder service, or both.

What changed: Depending on year and application, these engines could receive factory four-barrel induction, different carburetor calibration, freer exhaust, revised ignition curves, heavier cooling equipment, and other police, fleet, or special-duty supporting hardware.

What that did: The better induction and supporting equipment gave the 318 more useful output and, in fleet service, more ability to survive heat, idle time, and repeated hard acceleration. The Geezer still refuses to call one a disguised 340. A hotter workhorse is still a workhorse, and there is nothing wrong with that.

Where used: Selected factory four-barrel passenger-car, police, fleet, and special-duty applications.

Identification caution: This one earns the warning because four-barrel intakes migrate faster than police stories. Intake, carburetor, heads, exhaust, distributor, cooling package, engine stamping, application, drivetrain context, tags, broadcast sheet, and paperwork need to support the claim. An aftermarket four-barrel proves somebody owned a wrench.

Late Truck / Van 318 — Roller-Cam and Electronic-Fuel-System Versions

What it was: The later LA 318 kept working in trucks and vans after the old passenger-car version had already become yesterday’s news.

What changed: Depending on year, these engines could carry roller-cam valvetrain hardware, truck-specific oil pans and mounts, different exhaust manifolds, cooling and accessory drives, and later carburetion or throttle-body injection with the electronics that went with it.

What that did: Roller hardware made some later blocks attractive foundations for mild street builds, while the truck-specific equipment kept the engine useful under load. It also means a complete van engine can become half a project the instant somebody tries dropping it into an older car and discovers the pan, brackets, exhaust, accessories, and fuel system all have opinions.

Where used: Later LA-series Dodge truck and van applications.

The Magnum 5.2 is not another LA 318 variant. Same 318 cubic inches, related Chrysler small-block ancestry, but different heads, intake attachment, rocker system, pushrod oiling, valve covers, fuel injection, accessory layout, and engine-management hardware. Related is not interchangeable, and the parts counter remains perfectly willing to demonstrate the difference.

So the useful LA 318 ladder stays clean: ordinary two-barrel passenger-car engines, genuine factory four-barrel / police / special-duty combinations, and the later roller-cam / electronic-fuel-system work engines. Compression and emissions changes matter within those generations, but they do not need a new heading every time Detroit moved the timing curve. The 318 became famous by surviving almost everything. That does not mean every surviving one is the same engine.

↑ Back to the Top, Before the Casting Numbers Start Lying

---

Key Notes

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.

↑ Back to the Top, Before the Casting Numbers Start Lying

---

Bottom Line

The Mopar LA 318 is better than the haters say and less magical than the dreamers want. It became Chrysler’s small-block workhorse because it was durable, simple, common, and useful in everything from passenger cars and vans to trucks, police packages, and fleet duty. It was never supposed to be the glamour engine. It was supposed to start, pull, survive, and keep doing the job after everybody stopped admiring the valve covers.

That makes a healthy 318 an excellent choice when reliability, drivability, and sensible street performance matter. A reasonable combination can make one smooth, responsive, and genuinely enjoyable without pretending it has another displacement hiding inside. The 318 does not need to become a 340 to justify owning it, and a good street car does not need to win a bench-racing argument every time the hood opens.

Where the 318 loses the argument is when the horsepower target gets expensive. It does not have the 340’s bore and breathing room or the 360’s stroke and torque, and enough machine work and performance parts can eventually turn a cheap 318 into an expensive way to avoid starting with more engine. Big cams, oversized carburetors, weak compression, and lazy gearing do not create a sleeper. They create a 318 that sounds much more ambitious than it feels.

Condition matters more than the old claim that “318s run forever.” A complete, healthy engine with its brackets, pulleys, manifolds, pan, and supporting hardware can be an excellent foundation. A tired low-compression core assembled from mixed-year leftovers can consume plenty of money before it becomes anything worth driving. Common engines are easier to replace. They are not free to machine.

So build the LA 318 when a dependable, street-friendly Mopar small block is what the car actually needs. Keep the combination sensible, enjoy the durability, and move to a 340, 360, Magnum, or stroker foundation when the power goal genuinely calls for more engine. The 318 is a workhorse, and there is nothing wrong with that. Treat it like one and it earns its keep. Try to disguise it as something bigger, and the invoice eventually tells the truth.

↑ Back to the Top, Before the Casting Numbers Start Lying

---