Mopar LA Series V8 Engines: 318, 340, 360, and 273
by David Zatz
The LA engines were durable designs with high power capacity, the Chrysler's mainstay V8 for decades - and its only
V8 for many years, as well. The first "LA" engine, the 273, appeared in the 1964 cars; the basic design was used in the 2017 Viper V-10
Horsepower ratings before 1970 are gross measurements (without accessories). Ratings after 1971 are net, and are lower.
The LA was based on the company's first low-cost V8s, the A series
; but engineers needed to cut the weight, cost, and size of the engines, which dictated wedge heads with in-line valves. Spark plus were moved up, closer to the center of the combustion chamber, so they were above the exhaust manifold and easier to access than in the A and B engines. The wedge heads (first used by Chrysler on the B engines
) were far smaller, and lighter, than the old Hemi and polyspherical heads (318s with the poly heads are still often called "wide blocks" though the block itself is about the same size as that of the LA 318).
A new coring process at Chrysler's block foundry in Indianapolis allowed for thinner walls in the block, shedding fifty pounds and justifying the code LA ("Lightweight A"). The A-engine tappet bore machining was preserved to cut tooling expenses; the stroke was kept for most of the LA engines, too. In the end, it was far cheaper and faster to build than older Chrysler V8s, but no less durable - and, more efficient than the pricey polyspherical-head engines had been.
Thanks to Bill Watson, Joshua Skinner, Dan Stern,
Steven Havens, Jim Forbes, and Peter Duncan. Other information was provided by Willem Weertman's Chrysler Engines
The 273 carried over the A engines' crankshaft, bearings, bearing caps, vibration damper, and timing chain, and connecting rods (other LA engines used different rods)
|505 V-10||2002 - 2017||3.96||4.03|
|488 V-10||1991 - 2002||3.88||4.00|
The first engine in the LA series was the little 273, rated at 180 hp (gross) with a two barrel carburetor. In the 1965 cars, a four-barrel carb, new cam, and 10.5:1 compression pushed that up to 235 hp (280 lb-ft) in "Commando 273" form; and the 273 was made the base engine in the Plymouth and Dodge "intermediates," as well as being optional power for the Valiant and Barracuda.
In the 1966 cars, a 700 cfm carb and .500" lift cam moved the power rating up to very respectable 275 hp.
Engineer Pete Hagenbuch
LA (for Light A) engine
was developed with a wedge chamber, first as a 273 cid and then as a 318. Remember, this was the time the car lines expanded to three bodies, A, B and C. The 273 was limited to the A and B bodies, with the 318 engine in the C Body, which was new to Plymouth at the time.
Later came the 340
and then the 360, both with wedge chambers. And now, the one time state-of-the-art Mound Road Engine Plant is empty. The brand that used the majority of its production has disappeared too, to join ranks with names like Packard, Hudson, Desoto, Studebaker, Nash and Willys. ... It seems that a cherished name with a long history is not considered of value in this day and age.
He also said there was no performance drop in going from the old polyspherical heads to the wedge design:
The performance improved by getting rid of the silly polysphere.
A wedge chamber does have some advantages. One of the advantages is that you can build in a lot of what we call squish, where the chamber is just part of the cylinder head surface and the piston have a flat area that matches up with it ... It gets the charge moving and mixed, moving through the chamber at high velocity, which means the flame travel is fast and there isn't anything left to burn by the time it gets to top dead center, where you expect the detonation. [This allows the use of much higher compression ratios.]
|1967 283 V8||2 barrel||4 barrel|
|Gross hp (Valiant)||180 @ 4,200||235 @ 5,200|
|Torque (Valiant)||260 @ 1,600||260 @ 4,000|
|Bore and Stroke||3.63 x 3.31||3.63 x 3.31|
|Compression Ratio :1||8.8||10.5|
intake manifold was a hybrid single/dual plane design that
used one plenum for each side of the engine, joined by a carefully sized rectangular passage that solved
lean/rich problems that had occurred with the original "purely" dual plenum
design that had dedicated one barrel of the Carter BBD two-barrel carburetor to each bank. This
reduced the height of the engine and allowed
installation in the Valiant. (Thanks, Jim Deane.)
Since the bolt angle on the intake changed in 1966, the 1964-65 heads and intake are unique and cannot be interchanged with other LA engines or with the later 273. For the 1968 model year, Chrysler put a hydraulic cam into the 273.
1969 was the final year for the 273, its thunder having been stolen by the LA 318; but it still got a new manifold heat control valve (also used on the 318) with a disc-shaped counterweight. The next major change was the launch of the 340 cubic inch V8 in the 1968 cars; with bigger valves and other changes, it was clearly meant to be the performance leader of the Chrysler small-block V8s. One technician wrote that the 340 peaked at 5,600 rpm, while the 318 peaked at 4,400 rpm (with tests done every 400 rpm).
The 318 (5.2 Liter V-8)
Depending on how you look at it, Chrysler either bored out the 273 LA to create the 318, or upgraded the old A-series 318
to the new LA-type heads and block. Either way, American-made 1967 cars and trucks had the new engine; Canadian vehicles waited for a year. US-built trucks may have used the A-series as well, but production was definitely closed by 1968 (Thanks, Marcus Reddish).
The power ratings of the new LA-series 318 were exactly the same as those for the old polyspherical-head design, 230 hp and 340 lb-ft.
Generally, the 318 was a workhorse engine, using a single two-barrel carburetor for most of its life; it took regular gas, and provided good power, reliability, and, for a V8 of its time, economy. Hydraulic lifters, used from the start (and installed on A-engines starting with the 1968 model year), meant that owners did not have to do periodic adjustments.
|USA specifications||273 V8||318 V8 (LA)|| 340 V8|
|Gross horsepower, 1968|
(1962 for 318-A)
|190 @ 4400||230 @ 4400||275 @ 5000|
|Torque, lbs.-ft. , 1968||260 @ 2000||340 @ 2400||340 @ 3200|
|Compression ratio, 1968||9.0 to 1||9.2 to 1||10.5 to 1|
|Carburetor type (1968-73)||2-bbl.||2-bbl.||4-bbl.|
The 1969 model year brought a more reliable manifold heat control valve, using replaceable bushings for the valve shaft and a replaceable stainless steel internal seal to shield the bushings. Manifold heat control valve solvent can be squirted through the vent holes to keep the valve operating freely.
|1971 horsepower||155||235 @ 4,400|
|1972-75 horsepower||150 @ 4,000|
|1977 horsepower||145 @ 4,000|
|Torque, 1971 (SAE net)||260 @ 1,600||305 or 310|
|Torque, 1971 (gross)||230||340 @ 3,200|
|Torque, 1972-74||260 @ 1,600|
|Torque, lb-ft, 1975-77||255 @ 1,600|
|Compression (1971)||8.6 to 1||10.3 to 1|
|Compression (1973)||8.6 to 1||8.5 to 1|
As for the 340 Six-Pack, preliminary 1971 materials showed it at 250 horsepower, net, at 4,800 rpm; and torque was listed as 325 lb-ft (SAE net) or 345 (old-style), at 3,400 rpm.
Starting in 1973, Chrysler started using hardened valve seats to prepare for unleaded gasoline, since lead was being phased out of fuel. They did this by heating the seats to 1700°F and allowing them to air-cool.
| 1976 figures||Slant Six Valiant||318 V8 Valiant||360 V8 Valiant||440 Fury |
|Low speed pass||475 feet|
|405 feet /|
|High speed pass||2090 feet|
For 1977, F-bodies and B-bodies sold in high-altitude areas had altitude-adjustable carburetors; and the TorqueFlite torque converter was modified for better gas mileage and torque, with increased oil flow. The spark advance on these cars was also modified. Lean Burn was also set for a late 1977 launch on the 318 (except in California). Around this time, some 318 blocks were cast by International Harvester; they had the IH logo on the casting.
In 1978, Chrysler noted with regard to the 318 and 360:
The heat valve in the right exhaust manifold diverts hot gases to the floor of the intake manifold to vaporize the fuel mixture when the engine is cold. During warm-up, a thermostatic spring allows the heat valve to open to the exhaust pipe so gas flow through the intake manifold crossover passage is decreased.
All 1978 Chrysler V-8 and 6-cylinder engines have an adaptor to receive a magnetic probe for timing the ignition magnetically (you can still set the ignition with a timing light).
The engines had a second-generation Electronic Lean-Burn System for spark control, hydraulic valve lifters to avoid periodic adjustments, and cast iron cranks.
[It now has a] carburetor over a half pound lighter than the previous carburetor, designed for solid-fuel operation. This means a solid, continuous stream of fuel is fed to the primary discharge nozzles by the metering system. The fuel is mixed with air upon entering the nozzles. The solid-fuel metering produces precise carburetion for good driveability with lean fuel-air mixtures.
In California and some high-altitude locations, 1979 cars with the 318 had a Thermoquad four-barrel to boost performance in the face of primitive emissions systems; starting in 1981, the four barrel was available in trucks regardless of location.
In 1980, Chrysler altered the 318's block, cam, exhaust manifold, and rear main bearing cap to save weight.
The 1981 Diplomat and other M-bodies had an optional propane 318 system
- factory engineered, built, and warranteed, it proved to be popular. More interesting was the use of Chrysler's second
electronic fuel injection system (the first
was used on the '58s and was very similar in design).
he system was something of a rush job, without enough testing. It used a single continous-flow spray bar, and fuel flow was controlled by changing the fuel pressure. Engineer Richard Samul
wrote, "This system was prone to magnetic fields generated by power lines along roadways. This caused the fuel system to go rich at partial throttle and affected drivability." We have a large section on this system, with full details.
More successful was an attempt to replace the 360 with the 318 on 1981 model-year cars, essentially by using a four-barrel carburetor. The 318 four-barrel, used on police pursuit and other cars, produed 165 hp and 240 lb-ft of torque. The two barrel was, by now, down to a mere 130 hp and 235 lb-ft of torque.
318 throttle-body / roller-cam engines
by Vince Spinelli and Jack Perkins
In 1985, Chrysler switched from its original hydraulic lifters to a roller hydraulic lifter and a new matching camshaft; that both increased longevity (especially from cold starts) and allowed the company to use a steeper cam profile, and thus a more precise valve-train actuation. [Story of testing the roller cams
] The company also raised its compression from 8.7:1 to 9.0:1, bringing power up to 140 hp and 265 lb-ft, where it would stay until the end of 318s for passenger-car production in 1989.
Electronic fuel injection finally came to the 318 (and the 3.9 V6 based on it) in the 1988 Dodge trucks (but not cars). This was, in contrast to the Imperial's system, quite conventional, with a single dual-injector unit in the throttle body (one injector for each bank). Power output rose by a much-needed 20% to 170 hp and 280 lb-ft of torque. (In this year, oil capacity was reduced to five quarts, including filter.) See memories on the transition to fuel injection.
Though the low-pressure, dual-injector system was not all it could be, it dramatically improved the V8's driveability and reduced maintenance, boosting gas mileage and power alike.
The basic casting of the heads was the same, but the fine points were not; Chrysler added swirl intake ports to take advantage of the fuel injection. Since the pushrod angle was slightly changed by the taller lifters, the push rod guide holes were changed from roughly 0.5 inches to 0.66 inches. The push rods became shorter, and their diameter shrunk from 0.360" to 0.3125".
The 360 was upgraded in the following year - rising to 190 hp and 292 lb-ft of torque.
Magnum Engines (318/5.2, 360/5.9, 3.9 V6)
Chris Theodore said:
[After Chrysler bought AMC,] they tried to merge the two cultures, and so I was in charge of Jeep and Truck Powertrain. The first thing we started on were the Magnum engines, since the old 318 and 360
were still carbureted, and hadn't been improved in ages.
... Then they wanted to integrate the two groups, so they picked five guys from the Chrysler side and five guys from the AMC side, and moved me to Highland Park and some of the Chrysler Highland Park guys to the Plymouth Road
facility. We were all kind of like fish out of water.
The new engines came out on the 1993 Dodge Ram, Dodge Dakota, and vans. The main differences were in the high-swirl/high-flow heats, the better intake, and a sequential multiple-port fuel injection system which placed the injectors in the intake manifold, near the heads. This was controlled by a single-board computer, and fed by a returnless fuel supply with a higher-powered pump (aiming at a 90 psi fuel pressure). As with other Chrysler systems, the computer used signals from MAP (manifold pressure) sensor rather than a MAF (mass air-flow) sensor, calculating as needed. The Hall Effect crankshaft position sensor remained.
Horsepower shot up dramatically, from 170 to 230 hp, and the 280 lb-ft of torque stayed constant. That put the 318's power well above its best carburetor days. (The 360 had to wait a year, gaining Magnum power in the 1993 trucks and vans.)
wrote that "The Magnum blocks are physically the same as
the earlier LA engines, except the oil passage for the shaft mounted
rockers is not drilled, because the Magnum engines oil through the push
rods. The boss is there if you need to use the old style heads."
In 1996, as Dodge moved to the JTEC powertrain computer, the LA engine series gained OBD II on-board diagnostics, and EGR was dropped (late in the year for the 360).
The 340: high performance in a small package
The top LA engine for performance was almost certainly the 340 V-8, sold starting with the 1968 model year. It had high-flow heads, big ports, a
two-level intake manifold, and a six-barrel option (three two-barrel
carbs). (See the full page on the 340.)
There were many differences between the 340 and 318 apart from
the bored, which made the 340 far more powerful than the everyday 318.
The six-barrel version of the 340 had extra material in the bulkheads for strength, allowing the use of 4 bolt main caps; it also had a different cam and heads. That version was to form the basis of the most potent LA engines ever: the race-only 355 V8
Willem Weertman wrote that Chrysler wanted a low-cost engine between the 318 and 383 (like the B-series 361
); the result was the 360, which debuted in early 1971. It had a cast crank and external
balancing, and was the only LA engine
without a 3.31" stroke, going up to 3.58".
Raising the block decks would have been extremely expensive in tooling and time, so they cut the height of the piston to allow a little extra movement; and changed the radius of the crankshaft counterweights, so there would be more room at the bottom. To regain balance, they had to add weights to both ends of the crankshaft assembly, which meant redesigning the torque converter flex plate and flywheel, and adding an offset weight to the vibration damper on the front of the crank. There were numerous changes to the block, including movement of the core holes and higher-diameter main journals.
The initial power ratings were 255 hp and 360 lb-ft, gross, or 175 hp and 285 lb-ft of torque net - right between the 318 and 340. The 360 replaced the 383 as the optional engine in the 1971 Dodge Polara and Plymouth Fury, and the base engine in the 1971 Chrysler Newport.
For the 1974 Dodge line, a new variation of the 360 was made with a four-barrel carburetor, resulting in 200 hp and 290 lb.
With the loss of the 340, though, something had to be done; so Chrysler swapped many of the 340's performance parts to the 360, including the four-barrel carburetor and the 268-276-44 cam. This brought power levels back up to 245 hp, net, and 320 lb-ft of torque.
The 1975 model year brought up different issues; and another 360 variant with a four-barrel was produced for Califonia, with 190 hp and 270 lb-ft, and all emissions controls. The four-barrel had smaller primaries. Another version was produced for the Duster and Dart, with 230 hp and 300 lb-ft of torque.
360 was Chrysler's highest-performance V8 once the B-series engines were dropped in the late 1970s. It was used in patrol cars
and the Volare
Roadrunner and Kit Car - but was dropped in California at the end of the 1979 model year, and saw its final use in a sedan or coupe at the end of the 1980 model year. Still, it was popular in trucks and SUVs, eventually pushing the Grand Cherokee
5.9 Limited to become the fastest SUV.
Police pursuit heads, dubbed "J" heads, had slightly larger (1.88") intake valves, according to Dave Lyle, and the valve springs were stiffened.
As with the 318, all 360s had hydraulic lifters. In 1978, the 360 gained dual concentric throttle return springs in addition to a torsion throttle spring.
| 1978||Carburetor||Horsepower (net)|
|318 Fed.||Carter 2-barrel||145 @ 4000||245 @ 1600|
|318 (CA)||Carter 2-barrel||135 @ 4,000||235 @ 1,600|
|360||Carter 2-barrel||155 @ 3600||275 @ 2000|
|360 E58||4-barrel.||220 @ 4,000||280 @ 1,600|
|400||4-bbl||[email protected] 3600||305 @ 3200|
|400 HD||4-bbl||190 @ 3600||305 @ 3200|
The 1978 California version came with an air pump, which could be ordered elsewhere with the N96 emissions control package.
In 1989, the 360 switched to roller cams and low-pressure throttle-body fuel injection (see the 318 section); and see the Magnum section for details on the "5.9" or 360 Magnum engines.
All 360 production was moved to Mexico in 1980, according to
Rodolfo Rodriguez. United States' use of the 360 ended in December 2002.
Designed for aluminum engine blocks? (Mike Sealey)
is some evidence that the 273 was originally meant to be an aluminum-block engine, and was to power a stillborn A-body DeSoto. Motor Trend
enthusiast magazines' "future products" sections mentioned the development of both compact Dodges and DeSotos and a V8 engine sharing many
internal parts with the 318, but displacing about 270 cubic inches and
using an aluminum block. (At around the same time, the company was producing some aluminum block Slant Six
es, but the effort was deemed to slow and costly for the benefits.)
ran artist's conceptions of the
proposed Dodge and DeSoto
compacts; they accurately
predicted Dodge's use of the "Lancer" name, the grillework, and the
car's "character line," while missing on the taillight and rear
Identifying LA Series V-8 engines and parts interchange
LA engines have the distributor at the rear; and the displacement shown on the left front of the block, below the left cylinder head. Valve covers are held on by five screws; it is easy to overtighten them. A rubber gasket plus RTV seems to work well.
Robert Jones wrote: "All head gaskets for 318 LA series
engine, even from Chrysler, are
made to fit all bore sizes ranging from the 318 to 340. The fire ring
is much larger on a 340 and the gasket thickness is closely matched
to a 360 spec gasket, so the compression is reduced on replacement."
Dave Wordinger wrote: "The
1964-1965 273 head had the had the intake manifold bolt holes drilled
at a different angle than the other LA heads, but will bolt to any LA
block. The 1970 340-6 had the pushrod holes relocated. All other LA
heads are interchangeable. The heads don't care what kind of camshaft
or lifters you are using. The 1964-1967 273 had mechanical lifters. All
1968 and newer LA engines had hydraulics."
David William Elder
wrote: "If you compare an early (such as 1968) 340 crank to a 318 crank
of the same vintage you can clearly see the 340 casting is beefier. I
think the two are the same numerically speaking but as far as strength the 340 is clearly the winner. The same goes for the
connecting rods. The 273-318 connecting rods are similar to the 340s
but a different casting with less 'beef'. I have actually
seen some mid-70s truck and stationwagon 318s that came from the
factory with 340 Six-Pak rods."
Mark DuVerger wrote: "The 273 rods
are not the same as a 318, they measure the same and look identical but
are lighter; all 273 rods are full floating rods, 73
and up 318s are press fit rods for the wristpin. The 273 will rev a lot faster than a 318, or a 340."
Prichard wrote: "Any intake that fits an LA 318 will
also fit a 273. They will also fit 340s and 360s as well. But it is
easier to find a "non-smog" intake for a 273 or 318 than a 360."
See the starter page for information on starter interchangeability.
318 V8 Engine Troubleshooting
Duane D. Hughes wrote:
My 1976 318 stumbled and sagged badly until it was fully warmed up, even when new, a classic sign of a lean mixture. A friend who worked at a Dodge dealer advised me to raise the metering rods about 1/16 th of an inch, which can be done without disassembling the carb. I did this on three different cars with Carter carburetors, and it worked each time.
That car also pinged at light, not heavy, load, and on the slightest grade at highway speeds. I read that truck 318s had an adjustable vacuum advance on the distributor, accessible through the little hole where the vacuum line attaches to the vacuum advance unit. Sure enough, it had a screw to adjust the advance. Just a little playing around to get the right setting, and Voila! No more pinging. No change in mileage, either.
From: Bruce Martin wrote: One very common fault with the otherwise
wonderful 318 is that the exhaust crossover in the intake manifold
(which warms the base of the carb) becomes clogged. This is common so
it should be among the first things you check. (This problem was
addressed on the Magnum engines)
Ted Devey adds two more steps:
Timing marks and removing the crank seal (360 but 318 is probably similar)
- Examine the reluctor teeth in the distributor for possible damage,
nicks etc. which can happen if the gap gets too small. If there is
damage to the teeth, replace the reluctor.
- Several years ago I dismantled the Carter 2-barrel
carburetor and reassembled it with the jet assembly upside down. There
is no obvious wrong way.
The timing marks are located on the lower driver's side of the timing chain cover. If the car has extra brackets bolted on the bottom of the timing chain cover, they may hide the timing marks from being easily seen. Some early LA engines may have had the timing marks on the passenger side but certainly by 1977 they should all be on the driver's side. (Thanks, valiant67)
When the timing chain cover seal is leaking, the harmonic balancer will need to be removed. It will require a 1 1/4" socket and a puller to remove the balancer. You will then be able to replace the crank seal (and maybe add a wear sleeve to the crank if the surface is worn).
LA Series Components
(Thanks to Stephen Havens)
- 273 intake 1.78" exhaust 1.50"
- 318 with 2bbl same as 273
- 340 X heads 2.02 1.60
- 360 all including J head 1.88 and 1.60
|Engine||Setup and cam||Lifters||Lift||Duration|
|273||2 barrel through 67||Mechanical||395/405||240/240|
|273||2 barrel 68-69||Hydraulic||373/400||240/248|
|318||2 barrel 67||Hydraulic||390/390||244/244|
|318||2 barrel through 88||Hydraulic||373/400||240/248|
|340||4 barrel 68 man trans||Hydraulic||444/453||276/284|
|340 70||six pak||Hydraulic||430/444||268/276 (adjustable rockers)|
|360||2 barrel 71-74||Hydraulic||410/412||252/256|
Relevant LA V8 engine links
( repair tips | performance tips)
- 273 4V is AFB
- 78-85 318 is Thermoquad
- 86-91 318 is Quadrajet
- 68-70 340 is AVS
- 71-73 340 is Thermoquad
- 74-85 360 is Thermoquad
- 86-92 360 is Quadrajet
- 273 2bbl is Carter BBD 1 1/4"
- 67-73 318 is BBD 1 1/4" ( in 72 318 with A/C got Rodchester 2GV)
- 74-91 318 Holley clone of BBD 2GV and BBD were all used, though no BBD past 85
- 71-92 360 Carter BBD 1 1/2" and Holley clones post 85 maybe some Rochesters
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