Mopar 350 B-Series Big-Block Engine Specs

Intro

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

The Mopar 350 B-series is one of those engines that can confuse two different crowds before the hood is halfway open. Chevrolet people hear “350” and think they know what they are looking at. Mopar people hear “big block” and start expecting a 383, 440, or something with enough mythology to require crowd control. Both groups can put the guessing away. Chrysler’s 350 was a real low-deck big-block wedge, built for 1958, and it helped launch the B-engine family before the numbers everybody remembers took over.

Its importance comes from timing more than longevity. Chrysler was replacing a collection of older Hemi, Poly, and division-specific V8 thinking with a cleaner big-block wedge architecture that could serve several brands without every engineering department building its own private kingdom. The 350 and 361 were the opening move. The 350 disappeared quickly, but the basic low-deck B design it helped introduce stuck around for another twenty years. That is a pretty respectable legacy for an engine that barely had time to get its tools arranged.

The 350 was not some timid first draft, either. Plymouth’s Golden Commando version used dual four-barrels and carried a 305-horsepower rating, while the rare Bendix Electrojector fuel-injected version was listed at 315 horsepower. For 1958, that was serious hardware. The fuel injection was also serious trouble, which is why rarity and desirability need to be kept in separate drawers. A system can be historically fascinating and still make the owner stare at it like a dead refrigerator.

Other 350s were less dramatic. Dodge and DeSoto used lower-rated big-car versions in the 280- to 290-horsepower range, doing exactly the sort of work big late-1950s Mopars required. That spread is important because it keeps the engine honest. Not every 350 was a Golden Commando, and certainly not every one spent 1958 wearing exotic induction. Some simply hauled chrome, passengers, and enough sheet metal to qualify for its own zip code.

The 350’s short life is what makes it both interesting and inconvenient today. In a correct 1958 Plymouth, Dodge, or DeSoto, originality can give the engine real value because the 350 belongs to a very specific moment in Chrysler history. Sitting loose on a pallet with half the brackets missing, that same rarity changes personality. Suddenly the uncommon parts are not charming. They are things somebody has to find.

For a general performance build, the larger B and RB engines make a much cleaner argument. A 383, 400, 413, or 440 starts with more displacement, more builder familiarity, and fewer reasons to spend an afternoon explaining to the machine shop that no, this is not the Chevy one. The 350 can certainly be built into a good engine. It just makes little sense to choose the rare early displacement when horsepower per dollar is the entire assignment.

So the 350 B earns respect for what it actually did. It helped launch Chrysler’s modern low-deck big-block wedge family, carried real 1958 performance hardware in its best versions, and disappeared before the 383 could steal all the attention. Preserve one when the car and history justify it. Build one intelligently when originality is part of the point. Just do not make the little early B-block drag the muscle-era résumé of engines Chrysler had not built yet.

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Overview

Chrysler introduced the 350 B-series for 1958 as part of the first generation of its new low-deck big-block wedge family. The company had spent the earlier part of the decade juggling Hemis, Polys, and division-specific V8s, which produced plenty of interesting machinery and a parts catalog with all the organizational elegance of a junk drawer. The B engine was the rationalization move: one basic big-block wedge architecture that could be used across several divisions and enlarged as the product planners discovered new reasons to want more cubic inches.

The 350 used a 4.0625-inch bore and 3.375-inch stroke, giving it 350 cubic inches inside the new 9.980-inch-deck B block. Bore spacing was 4.800 inches, rod length 6.358 inches, and the basic engine used the five-main-bearing, pushrod, wedge-head arrangement that would define the low-deck B family. The important dimension is the stroke because Chrysler kept that same 3.375 inches through the 361, 383, and 400. From there the engineers mostly reached for a larger boring bar.

The 361 launched beside it using the same stroke but a 4.125-inch bore. That makes the relationship between the two beautifully simple. The 350 was not an unrelated oddball that happened to arrive at the same time. It was the smaller-bore version of Chrysler’s new low-deck idea. The 361 had slightly larger cylinders and therefore more displacement. Anybody trying to identify one by confidence and valve-cover shape is volunteering for remedial measuring.

Plymouth gave the 350 its most memorable job with the Golden Commando. In its better-known high-output form, dual four-barrels helped produce a 305-horsepower rating. That was not decorative carburetion added so the air cleaner could occupy more acreage. Chrysler was making a real performance statement with the new wedge engine, and the Golden Commando gave the 350 a brief moment when it could stand at the front of the showroom instead of being remembered later as “that one-year B-block.”

Then came the Bendix Electrojector version, rated at 315 horsepower, and here history becomes considerably more interesting than ownership. Electronic fuel injection in 1958 was ambitious, rare, and troublesome enough that many systems did not remain on the engines that originally received them. That makes a genuine surviving setup historically important, but it also means an Electrojector claim needs more than a fuel line, an old photograph, and somebody saying his uncle remembers it.

The rest of the 350 story was more ordinary and therefore easier to forget. Dodge and DeSoto used lower-rated versions around 280 and 290 horsepower in big-car applications. Those engines were not failed Golden Commandos. They were doing a different job. Late-1950s cars were large, heavy, and expected to move with enough authority that the owner did not regret buying the expensive model. A big-block wedge with healthy torque was exactly what the assignment called for.

Dodge identification deserves extra caution because the D-500 name carries enough performance shine to attract engine stories like a porch light attracts bugs. The 1958 D-500 identity is more strongly associated with the 361 B engine, not the 350. That does not mean no 350 ever lived under a Dodge hood. It means nobody gets to attach D-500 money to a 350 until the car, engine, application, and documentation all agree. Badges are removable. History is supposed to be harder.

The short production run is one reason the 350 vanished from the collective memory so quickly. Chrysler already had the larger 361 in production, and the 383 followed soon enough to become the familiar low-deck big block. Once the 383 started doing everything from big-car duty to serious muscle work, the 350 became the relative who helped build the house and then moved away before anybody took family pictures.

That short run also shapes rebuild economics now. Bore-specific pistons, early induction, brackets, pulleys, linkage, air-cleaner hardware, exhaust pieces, and restoration details can be much harder to replace than ordinary later B-engine parts. Some pieces interchange across the broader family. Some do not. Some can be adapted if originality has already been thrown overboard. The correct answer depends on whether the goal is restoring a 1958 car or merely finding someplace to bolt a big-block Mopar.

The low-deck B versus raised-deck RB distinction also needs to stay nailed to the wall. The 350 belongs to the B family. The 413, 426 wedge, and 440 belong to the taller RB family. They share Mopar big-block ancestry, but deck height changes intake width, valley dimensions, rotating geometry, and other hardware assumptions. “It’s all Chrysler big-block stuff” works right up until the intake manifold is suspended above the heads like a bridge somebody forgot to finish.

Inside the engine, the 350’s 4.0625-inch bore also deserves respect during machine work. A shop familiar with later 383s and 440s still needs to treat the engine as the 350 it is. Bore size, piston choice, compression height, head chamber volume, valve clearance, gasket selection, camshaft, and intended use all need to be planned around the actual block rather than the better-known Mopar somebody has rebuilt twenty times.

That becomes especially important because the engine’s best modern use is usually restoration-aware rather than maximum-effort performance. A sensible compression ratio, mild camshaft, correct or appropriate induction, healthy ignition, good cooling, and freer exhaust can make a 350 pleasant without turning the project into an archaeological dig for horsepower. There is no prize for destroying rare early parts while trying to prove a larger B engine would have been cheaper.

Compared with the 361, the 350 is the rarer, smaller-bore first-year sibling. Compared with the 383, it gives up displacement, parts familiarity, and nearly all the later muscle-era reputation. Compared with the 400, it gives up enormous bore area and most modern stroker appeal. That leaves the 350 with a narrow but legitimate strength: it is the correct engine for certain 1958 Mopars and an important piece of the B-series beginning.

That is enough reason to save one when the car deserves it. A complete, documented 350 in the right Plymouth, Dodge, or DeSoto contributes to the historical identity of the vehicle in a way a later swap cannot. A genuine Golden Commando combination deserves even more care, especially when the original dual-quad or rare fuel-injection hardware survives. Once that context disappears, however, the engine has to compete with larger, easier, and cheaper Mopar big blocks, and sentiment starts losing ground to machine-shop arithmetic.

The 350 was not Chrysler’s greatest big block. It was the first small step in a family that soon produced much bigger reputations. That is precisely why it belongs in the story. Chrysler built a modern low-deck wedge, gave it real performance hardware right out of the gate, then immediately started enlarging the cylinders. The 350 opened the door. The 361 walked through it. The 383 kicked the thing off the hinges.

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General Specs

Displacement	350 cu in / 5.7L	Bore / Stroke	4.0625 in × 3.375 in
Production / Use Era	1958 early Mopar low-deck B-series passenger-car era	Bore Spacing	4.800 in
Engine Family	Chrysler / Mopar B-series low-deck big-block wedge V8	Deck Height	9.980 in
Block Material	Cast iron	Rod Length	6.358 in
Cylinder Head Material	Cast iron	Main Journal	2.625 in
Fuel / Induction	Gasoline; carbureted, 2-barrel or 4-barrel by version	Rod Journal	2.375 in
Cam Location	In-block camshaft	Main Bearings	5
Valve Layout	OHV / pushrod, 2 valves per cylinder	Firing Order	1-8-4-3-6-5-7-2
Common Main Caps	2-bolt	Distributor Rotation	Counterclockwise
Rear Main Seal	2-piece	Weight	~650–700 lb complete iron big-block, depending on accessories/configuration
Balance	Internal balance	Dimensions	~29H / ~29W / ~30L

Exact parts and specs can still vary by vehicle line, performance package, service history, and whether somebody already mixed parts without checking what actually fits. Use these numbers as the family baseline, then verify the actual block, crank, heads, induction, main-cap configuration, balance parts, and application before ordering parts or machining anything expensive.

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Variants

The 350 B-block only lasted through 1958, but Chrysler managed to give the little first-year big block more personalities than its one-year résumé suggests. Ordinary Dodge and DeSoto versions handled big-car duty. Plymouth’s Golden Commando stepped up to dual four-barrels. Then Bendix Electrojector fuel injection arrived and proved Detroit was perfectly capable of getting ahead of itself before most garages had figured out automatic chokes.

1958 Dodge / DeSoto 350 — Passenger-Car Versions

What it was: These were the more ordinary 350 B-series applications used in large Dodge and DeSoto passenger cars. Same new low-deck B architecture, same 4.0625-inch bore and 3.375-inch stroke, but without the exotic induction that made the Plymouth Golden Commando famous.

What changed: The supplied material identifies lower-rated Dodge and DeSoto combinations around 280 and 290 gross horsepower. Exact induction and calibration varied by application, so there is no reason to manufacture separate variants where the surviving specification material does not establish different hardware packages clearly enough.

What that did: These engines supplied the torque and smooth road power a late-1950s Mopar needed without pretending every full-size sedan had wandered out of a performance catalog. A 280-horsepower big block was hardly punishment in 1958, even if history later became distracted by everything with two carburetors.

Where used: 1958 Dodge and DeSoto big-car applications.

Identification caution: Dodge’s better-known D-500 performance identity is more strongly associated with the 361 B engine. A 350 does not become a D-500 engine because the badge, air cleaner, or seller gets enthusiastic. Vehicle application, engine identity, dates, and documentation need to agree.

1958 Plymouth Golden Commando 350 — Dual Four-Barrel

What it was: This is the 350 most people remember. Plymouth took Chrysler’s brand-new low-deck wedge and gave it enough induction to make sure nobody mistook the new B-series for an economy experiment.

What changed: The Golden Commando used dual four-barrel carburetors on the 350 B-series package. That is a genuine induction change, not a later carburetor swap being promoted by nostalgia.

What that did: Output reached 305 gross horsepower. For a first-year big-block family in 1958, that was serious business. The extra induction let the engine breathe well enough to establish performance credibility before the larger 361 and 383 had time to steal the furniture.

Where used: 1958 Plymouth Golden Commando performance applications.

Identification caution: Dual four-barrel equipment has had sixty-plus years to migrate between engines. Intake, carburetors, linkage, air-cleaner hardware, heads, camshaft, compression, exhaust, dates, and original vehicle application all need to support a Golden Commando claim before the asking price starts acting important.

1958 Golden Commando 350 — Bendix Electrojector Fuel Injection

What it was: This was the exotic one. Chrysler substituted Bendix Electrojector electronic fuel injection for carburetion and produced one of the earliest American production attempts at electronic gasoline injection.

What changed: The Bendix system replaced the conventional carburetor arrangement with electronically controlled fuel injection and its associated hardware. That was an enormous technological leap in 1958, which also explains why ownership could turn into an electrical-engineering correspondence course.

What that did: The fuel-injected 350 was rated at 315 gross horsepower, ten more than the dual-quad Golden Commando. Historically, it is fascinating. Practically, the system developed enough trouble that many original installations were later converted back to carburetors.

Where used: Extremely limited 1958 Plymouth Golden Commando applications equipped with Bendix Electrojector injection.

Identification caution: This claim earns the full inspection. Genuine Electrojector hardware is rare, many original systems disappeared, and an engine that once had injection may no longer carry it. Injection hardware, wiring and controls, engine configuration, dates, vehicle application, and documentation all need to agree. An empty mounting hole and a family story are not fuel injection.

That is the useful 350 variant map. Ordinary Dodge and DeSoto versions handled big-car work. The dual-quad Golden Commando supplied real performance hardware. The Electrojector version added historically important electronic fuel injection and another ten horsepower along with considerably more opportunity for aggravation. One year, three genuinely different levels of ambition, and then Chrysler enlarged the bore and moved on.

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Key Notes

The Mopar 350 B-series is the kind of engine people ignore until a 1958 car makes their parts-counter guesses look stupid. It was part of Chrysler’s first low-deck B-engine push, not a Chevy 350, not a small-block Mopar, and not some later 383 wearing an early disguise. The number causes confusion because half the garage hears “350” and starts thinking about the wrong brand before the coffee cools.

The basic fingerprint is 4.0625-inch bore and 3.375-inch stroke in the low-deck B-series architecture. That puts the 350 in the same family neighborhood as the later 361, 383, and 400, but it doesn’t make those engines interchangeable piles of wishful thinking. Bore, pistons, compression height, application hardware, and early-year details still get a vote.

The 350 and 361 are close enough to make lazy identification dangerous. They share early B-series blood and the same stroke, but the bore difference is real. A 350 isn’t a 361 with bad handwriting. If the block, bore, crank, pistons, and application don’t agree, the machine shop will eventually explain the mistake with a bill.

The B versus RB split also needs a fence around it. The 350 is a low-deck B engine. The 413, 426 wedge, and 440 are raised-deck RB engines. Deck height changes intake fit, valley width, top-end assumptions, and build planning. “Mopar big-block” is a family argument, not a parts order.

The Golden Commando name deserves respect, but it doesn’t replace evidence. A correct Plymouth 350 with dual four-barrels is a real piece of 1958 performance history. The rare Bendix Electrojector version is even more interesting, and usually more troublesome. Either way, carburetion, intake, heads, cam, compression, exhaust, application, dates, air cleaner, linkage, and documentation need to line up before the price starts acting brave.

The 350’s original application matters more than the displacement number. In the right 1958 Plymouth, Dodge, or DeSoto, a complete 350 B can be an important restoration piece. As a loose engine on the floor, it has to prove itself harder. A complete early package is one conversation. A mystery core missing half the hardware is another, and that second conversation usually smells like shipping costs.

Parts support is the practical warning. Later B/RB engines get more attention, more aftermarket help, and more builder familiarity. The 350 may share family architecture, but early-specific induction, pistons, brackets, pulleys, linkage, air-cleaner hardware, exhaust pieces, dress parts, and restoration hardware can still turn into a hunt. Missing parts on a short-run engine aren’t charming. They’re invoices waiting for a box.

Machine work and build planning need to match the actual engine, not the closest better-known Mopar in somebody’s head. Bore size, crank stroke, piston choice, compression ratio, cylinder-head compatibility, intake fit, cam selection, valve clearance, and intended use all need checking before money starts flying. A shop that knows 383s and 440s still needs to slow down before treating a 350 like a warm-up exercise.

The right build is usually mild, clean, and restoration-aware. Keep the original pieces when they belong. Use sensible compression, a reasonable cam, proper ignition, good cooling, clean fuel delivery, and exhaust that helps without turning the car into a fake drag-strip refugee. This engine can be interesting and useful when it’s built for what it is.

The wrong build is cheap-power fantasy. If the goal is easy Mopar big-block torque, a 383, 400, 413, or 440 usually makes more sense. Those engines are easier to feed with parts, easier to explain, and usually better suited to horsepower work. The 350 B is worth saving when correctness, completeness, and early Mopar identity matter. It’s a rotten shortcut when the plan is big power and the homework got left under the creeper.

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Bottom Line

The Mopar 350 B-series matters because it helped launch Chrysler’s low-deck big-block wedge family in 1958, not because it became the engine everybody spent the next decade chasing. It is a real Mopar big block, a real part of the B-engine beginning, and a very different animal from the Chevrolet 350 that steals the number in most conversations. The 350 B opened the door. The 361, 383, and 400 were the engines that stayed around long enough to furnish the room.

Its strongest argument is originality. In a correct 1958 Plymouth, Dodge, or DeSoto with the proper early hardware still present, the 350 can be exactly the engine that belongs there. A Golden Commando or other documented period package deserves even more care when the parts and application support the claim. Pulling one out simply because a later big block is easier can turn a historically correct car into a faster vehicle with a weaker story.

Its weakest argument is horsepower per dollar. Once originality stops mattering, the 350 has to compete with larger B and RB engines that offer more displacement, broader parts familiarity, and fewer early-production headaches for roughly the same machine-shop appetite. A 350 can make a fine mild driver, but choosing one as a cheap path to serious Mopar big-block power is starting the race with one shoe untied.

Buying one requires more skepticism than excitement. A loose core needs the block, bore, stroke, heads, induction, dates, accessories, application, and completeness checked before somebody charges extra for Golden Commando history, rare fuel-injection stories, or simple scarcity. Rare can mean desirable. It can also mean the missing bracket costs three weekends and enough money to make common parts look beautiful.

So save the 350 B when the car, hardware, and history give it a reason to stay. Build it mildly, protect the hard-to-replace early pieces, and let it be the clean first-generation wedge it actually is. Do not overbuild it into an imitation of the larger engines Chrysler produced almost immediately afterward. The 350 earned its place by starting the B-series story. It does not need somebody else’s muscle-era résumé stapled to it.

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