Mopar LA Series Engines
3.9 - 5.2 - 5.9 - 273 - 318 - 340 - 360 - 355 (Racing)
Thanks to Bill Watson, Joshua Skinner, Dan Stern, Steven Havens, Jim Forbes, and Peter Duncan for their contributions. Much information was provided by Carl Payne and the Mopar V-8 Engines book.
The LA engines were modern, relatively efficient, and extremely durable designs that became the mainstay of Chrysler's cars and trucks for decades - a fact which would probably have surprised their designers, given the pace of engine development at the time. A dizzying variety of engine variations were being produced in the 1950s and 1960s, steadying out in time so that the 318 and 360 cubic inch sizes remained for over thirty years each. The basic design is still in use, in the Viper V-10 and a racing-only LA-based four cylinder.
|488 V-10||1991 - 2002||3.88||4.00|
|505 V-10||2002 -||3.96||4.03|
|* “They put the 360 in a few of the trucks in early 2003.” — Rovell Rangel|
The A engine was produced from 1955 through 1966. The LA, introduced in 1964, had the same basic design but was very heavily modified. The lightweight ("L" A) or thin-wall casting and heads saved around 50 pounds; the wedge-shaped combustion chamber was much smaller than the A engines’ poly heads, greatly reducing the size and allowing the first LA engine (273 V8) to fit into the small Valiant. The LA's valves were simpler too, saving money and size. The 273 ended up being only fifty pounds heavier than the 225-cid slant six.
Bill Watson noted that the 273 carried over the A engines’ crankshaft, bearings, bearing caps, vibration damper, and timing chain, and conecting rods (if you want to interchange them, though, you need a 273; the 318 and other engines used different rods.). The LA bore was smaller, though the stroke was the same, and camshafts could not be shared.
- Upgrading LA engine performance
- The 3.9 liter V6: LA V6 engine (based on the 360)
- Four-cylinder LA racing engine (no, that's not a typo!)
- Putting the 318 into a Toyota Celica
- Propane 318 system
- Dodge Truck V10
- Interview with an LA engine designer, Pete Hagenbuch
- Interview with an LA engine designer, Willem Weertman
The first LA was the 273, with a two barrel carb, producing 180 gross hp. In 1965, a four-barrel carb and high performance cam could push that up to 235 hp; and, in 1966, a limited edition 273 with a 700 cfm carb and .500" lift cam put out 275 hp.
Engineer Pete Hagenbuch said:
The 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 or B 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. And 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. Next to join this group will be Oldsmobile, another of the pioneer nameplates to be tossed aside. It seems that a cherished name with a long history is not considered of value in this day and age.
|1967||273 V8||273 V8|
|Carburetor||2 barrel||4 barrel|
|Manual transmissions||3 or 4 speeds||4 speeds|
|Gross horsepower (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|
|Standard Tire/Wheel||7 x 13 (wheel 4.5) (Valiant)|
The intake manifold was special hybrid single/dual plane design that incorporated two plenums, one for each side of the engine. They were joined by a specially sized rectangular passage that solved lean/rich problems that occurred with the initial, purely dual plenum design that dedicated one barrel of the BBD to each bank. This was done to reduce the overall height of the engine and allow installation in the (originally /6 designed) Valiant engine compartment. (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.
In 1968, the 273 got a hydraulic cam; the forged steel crank was replaced with a standard nodular cast iron crankshaft to save money. 1969 was the final year for the 273, its thunder having been stolen by the 318, which was introduced in 1967; but it still got a new manifold heat control valve (also used on the 318) with a disc-shaped counterweight.
The 318 (5.2 Liter V-8)
The new, LA type 318 was brought out in 1967; the main difference from the 273 was its larger 3.91” bore. There could be some confusion over the two 318 V8 engines, one using the old A type design, the other using the lightweight LA type. According to Mark Koskenmaki, all 1967 A-type 318s came from Canada, while vehicles built in the US had the new LA 318. The A-engines did not last past 1967.
The LA 318 was never used as a performance engine by Chrysler, unlike the 318 A-engine; the 273 four-barrel matched it in peak horsepower, and the more performance-oriented 340 was quickly released in 1968. Even after the 340 was dropped, the 360 was used for performance applications.
|USA specifications||273 V8||318 V8 (LA)||318 V8 (A)|| 340 V8
|Gross horsepower, 1968
(1962 for 318-A)
|190 @4400||230 @ 4400||200-260 @ 4,400||275 @ 5000|
|Net horsepower, 1972-73||150 @ 4,000||240 @ 4,800|
|Net horsepower, 1977||145 @ 4,000||(not made)|
|Torque, lbs.-ft. , 1968||260@ 2000||340 @ 2400||340 @ 3200|
|Torque, lb-ft, 1972||260 @ 1,600||290 @ 3,600|
|Torque, lb-ft, 1977||245 @ 1,600|
|Compression ratio, 1968||9.0 to 1||9.2 to 1||9.0 to 1||10.5 to 1|
|Compression ratio, 1973||8.6 to 1||8.5 to 1|
|Carburetor type (1968-73)||2-bbl.||2-bbl.||2 or 4 bbl (1960s)||4-bbl.|
318 was used as a police engine, mainly in the M-bodies
(Diplomats and Gran Furys), but its performance was unexceptional. It was, in many years, the largest engine available
in Valiants and their descendents, the Diplomat and Gran
Fury. It was used extensively in trucks as well.
A new, more reliable manifold heat control valve was used starting in 1969, featuring 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.
From its introduction in 1967 through its conversion to EFI, the 318 was generally treated as a two-barrel workhorse. With the 340 and 360 around, the 318 kept its "economy carb" from 1968 through 1978, when it got a Thermoquad four-barrel option to make performance acceptable with California emissions systems (in some years, the only choice in California was a four-barrel). A Carter two-barrel was the official replacement for the Imperial electronic fuel injection system. Starting in 1981, the four barrel was available in trucks regardless of location.
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).
In 1978, Chrysler noted with regard to the 318 and 360:
Exhaust-valve seats are induction-hardened on all engines for lead-free fuels. In the hardening process, seats reach a temperature of 1700°F and are then allowed to air-cool. This hardens the valveseat surfaces to a depth of .05" to .08". The exhaust-valve stems are chrome-plated for increased resistance to wear.
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); magnetic settings are more accurate.
Chrysler's most compact V-8 designed to be rugged and dependable - is equipped with the second-generation Electronic Lean-Burn System for 1978. Features include:
- Hydraulic valve lifter (tappets)-no periodic adjustments required
- Induction-hardened exhaust-valve seats
- Cast ductile iron crankshaft
- Aluminized steel exhaust and tail pipe
The 318 V-8 has proved its reliability over the years as the best seller in Chrysler Corporation's lineup of V8 engines. Now, it offers the increased dependability of electronic spark-plug timing and ignition controls. (A four-barrel version to meet California emission requirements is available on LeBaron and Cordoba in California).
1976 figures Slant Six Valiant 318 V8 Valiant 360 V8 Valiant 440 Fury Low speed pass 475 feet / 11.0 sec 460 feet / 10.5 sec 405 feet / 8.6 sec 400 feet / 8.4 sec High speed pass 2090 feet / 24.8 sec 1480 feet / 16.2 sec 1245 feet / 13.3 sec 1130 feet / 11.7 sec
[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 1980, Chrysler altered the 318’s block, cam, exhaust manifold, and rear main bearing cap to save weight. They advertised the following specifications:
Bearings, Camshaft—Steel-backed Babbitt, five, replaceable
Bearings. Connecting-Rod, Lower—Aluminum on steel.
Bearings, Crankshaft, Main—V-8: five babbitt (except #3 aluminum), replaceable.
Oil grooves in upper and lower # 1 bearing, in upper half of all others.
2.50" x 0.872"
2.50" x 0.872"
2.50" x 1.51V
2.50" x 0.872"
2.50" x 1.322"
For 1981, Chrysler introduced a propane 318 system in the M-body cars. Factory engineered, built, and warranteed, it proved to be very popular for propane.
318 throttle-body / roller-cam engines (by Vince Spinelli and Jack Perkins)
In 1985, Chrysler finally switched from standard hydraulic lifters (and matching camshaft) over to a roller hydraulic lifter and a new matching camshaft. The roller design allowed for a steeper cam profile, and thus a more precise valve-train actuation, but the primary impetus seemed to be longevity. [Story of developing the roller cams]
The throttle-body fuel-injected 318 motor had a few changes for its model year (1988), which would come to the 360 in 1989. This low pressure system gained a twin-bore throttle body with dual fuel injectors; the new throttle body had a 32.5% increase in throttle area. The engine also used new roller tappets and revised valve timing, increasing power output of the 318 by 20% (and also boosting the 360 when its turn came). Oil capacity was reduced to five quarters (with filter change).
The heads were different; the basic casting is the same, but the fine points were not. To make better use of the fuel injection, swirl intake ports were introduced. To accommodate a slightly changed pushrod angle (the new roller lifters were taller than the standard hydraulics), the push rod guide holes in the cylinder heads were changed from roughly 0.5 inches to a published 0.66 inches (Dodge DW Series Truck Factory Service Manual, 1988). Upon measurement, this was confirmed to within an accuracy of 0.01 inches. Push rod length changed from about 7.5” down to 6.78”, and diameter shrunk from 0.360” to 0.3125” (again to accommodate the changed push rod angle).
[See the Magnum section, later in this page, for details on the "5.2" or 318 Magnum engines.]
318 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:
- 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.
Timing marks and removing the crank seal (360 but 318 is probably similar)
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).
The 340: high performance in a small package
Probably the best development for performance enthusiasts was the production of the 340 V-8 in 1968. It had high-flow heads, big ports, a two-level intake manifold, and a six-barrel option (three two-barrel carbs).
There were many differences between the 340 and 318 apart from the bore of a similar block. The 340, from '68 to '71 at least, is the smallblock equivalent of the Hemi. It has great power when put in the right car (a '68 Barracuda, for example), and has more than enough appeal to keep the Brand-X guys wishing they'd boarded the Mopar Express before the light turned green.
355 Racing Engine: NASCAR, Drag Racing, and IROC
Starting around 1975, Chrysler produced a version of the LA engine specifically designed for racing, and not available in any passenger car. NASCAR had recently started penalizing of any engine over six liters (366 cubic inches). In 1975, Dodges equipped with the 355 V8 won 14 of 30 Grand National races, and Richard Petty was in the winner’s circle 13 times with 355-powered Dodges.
Sometime around 1978, a drag-racing version of the engine was developed, also at 355 cubic inches. Marc Rozman wrote:
When I ran my 440, a guy we called Fast Eddy [Poplawski], part of the race group, who ran a 355 racing motor [for drag racing; never used in a production car], tunnel ram, dual quads. He had a Chevy manifold on a Mopar, he made up little wedges that make a manifold fit the angle on the heads on the small block Chrysler. Back then, Ted Flack and Howard Comstock where the guys driving those cars. Ted Flack was a dyno operator at one time, and he made the grade and became an engineer later on. Sharp guys.
They were still running the [NHRA] Pro Stocks, and if you look in the records you can see the Flack and Comstock cars, including a Dodge Dart Sport. They were doing development work on that motor still.
Ed Poplawski wrote:
The 355 engine was a bored and stroked 340 production 6-barrel engine block (LA) that we modified for racing use. The modern 355 that we did in 2001 when we got back into NASCAR racing is a purpose built race engine which has nothing in common with any of our old or new LA engines.
[The 355 block was common to all racing applications before 2001.] Back then the engine block of choice was the 340 6-barrel block. However, by the late 1970s, 6-barrel blocks were hard to come by and we were scrounging the local junk yards trying to find blocks. It was the same thing for the Pettys. To be honest, we were using standard 340 blocks for dyno development and saving the 6bbl blocks for the race cars.
The reason we wanted to use the 6bbl block was because we had added material to the bulkheads for strength so we could use 4 bolt main caps. Otherwise the only difference between the engines, like you mentioned was carburetion, camshaft, cylinder heads and headers. The NASCAR engine could only use a flat tappet cam (we used a mushroom tappet) and a single 4 bbl carb. The NHRA drag engines could use roller cams and multiple carburetion intake manifolds depending on the class.
Headers were chosen depending on the type of racing we were doing and the engine speed at which we were running. For example, for 1978 our goal for Daytona that year was 600 HP and the engine peaked at 7200 rpm. The 8bbl drag engines peaked at 9600 rpm so therefore the header size and length was a lot different. The IROC engines were basically NASCAR 355 engines. Also, we used dry sump oil systems in NASCAR so there were some internal modifications done to the block to make this work. Those were the major differences between all the series.
For 1976, Dodge had a complete W2 package, developed under John Wehrly; Willem Weertman credits Larry Rathgeb with creating a Kit Car which included that engine for racers. The Kit Car had a 340, 355, or 360 cubic inch engine (it varied by model year). The 355 had a slightly larger bore than most LA engines, with a stroke between the 340 and 360 (see chart at beginning of page); it did well in short-track venues. The engine had forged aluminum pistons, stress-relieved blocks with thickened bulkheads, and four-bolt instead of two-bolt main bearing caps. Weertman wrote that this package reached more than 600 hp, gross, with a single four-barrel carburetor.
In 1979, Mopar Performance started selling their “X block,” a heavy duty racing small block which would displace 340 cubic inches used as is, or could be bored out, as Larry Shepard suggested, to 355 cid (Shepard also warned against using a used Kasper prototype block). These were painted orange and a large “X” was cast into the end. It had standard and four bolt versions. The same block was used in Pro Stock during 1979 and in NASCAR racing , as well as ARCA oval track racing in the 1990-91 seasons. There were numerous features in this block to add strength.
The engines were also used when Chrysler sponsored the IROC (International Race of Champions) series, which uses identical cars; drivers ran with Dodge Daytonas converted to rear wheel drive, with the 355 under the hood.
When NASCAR added a truck series in 1996, Dodge entered with an updated version of the 355, including cylinder heads. The engine was finally retired in 2001. [Read a 355 development story]
The 360 first appeared in 1971, with a two barrel carb. It had a cast crank and external balancing, and was the only LA engine without a 3.31" stroke (3.58"). In 1972, it was rated at 175 hp @ 4,000 rpm, and 285 lb-ft of torque @ 2,400 — above the 318 but well below the smaller 340. According to engine leader Willem Weertman, the goal of the 360 was to replace the old B-series 361, providing something between the 318 and 383; but to do so at lower cost. They could not raise the block decks to help with a longer stroke, because the budget did not include altering the automated block and assembly lines to that extent. Weertman and others worked around that, using the same connecting rod as the 318, but reducing the height of the piston from the pin to its top, and cutting the radius of the crankshaft counterweights so there would be room at the bottom of the stroke. While that solved the space issues, the engine was now out of balance, so weights were added to both ends of the crankshaft assembly. That meant redesigning the torque converter flex plate and flywheel, and adding an offset weight to the vibration damper on the front of the crank.
The 360 was relatively tame through 1974, when it received some 340 performance parts and a Carter Thermoquad four-barrel carb in an effort to replace the 340 as a performance engine (starting in 1985, a GM-Rochester Quadrajet replaced the Thermoquad).
In its final years, the 360 was Chrysler's performance truck engine, making the Grand Cherokee 5.9 Limited the fastest SUV and powering top-of-the-line Dakotas and Durangos. The 360 was also used in patrol cars and the Volare Roadrunner. In 1987, a number of 360s were used in Diplomats and Gran Furys; some say that some of these engines were labelled as 318s, but that's a tough one to track down.
Vince Spinelli and Jack Perkins added: “There are squad car heads, and there are interceptor heads. Squad car (cruiser) heads are 360 heads with little to no modification depending on whom you talk to. Interceptor heads are high compression heads, identical to standard 318 heads of the era, but with a smidge tighter combustion chamber. Compression works out to high 9s to 1, as opposed to the standard 318 head at about 8.5 to 1. Interceptor heads also have slightly large valve aperatures.”
Dave Lyle expanded on this: “These were J heads, and they were the same as regular 360 heads, except for bigger intake valves (1.88) and better springs.”
In 1978, Chrysler wrote that the 360’s “valve timing, valve lift and length of time the valves remain open are carefully engineered for low emissions, power, and smooth operation at all speeds. Hydraulic valve lifters require no periodic adjustments. ... The camshaft is designed to seat the valves smoothly to decrease the possibility of valve bounce and the stress it causes in valve stems.” In 1978, the 360 gained dual concentric throttle return springs in addition to a torsion throttle spring.
|1978||Carburetor||Horsepower (net)||Torque (lb-ft)|
|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||190@ 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 throttle-body fuel injection (see the 318 section); and see the Magnum section, later in this page, for details on the "5.9" or 360 Magnum engines.
All 360 production was moved in Mexico in 1980, according to Rodolfo Rodriguez. United States use of the 360 ended in December 2002.
Designed for aluminum engine blocks? (Mike Sealey)
There 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 and other 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.
Motor Trend ran artist's conceptions of the proposed Dodge and DeSoto compacts. Their sketch of the Dodge accurately predicted its use of the "Lancer" name, its grillework, and the character line that curves back toward the front of the car in the middle of the front door on production Lancers. The taillight and rear fender treatment looked rather more like that of the 1960 Dodge Polara than what actually went into production.
The DeSoto sketch showed a Valiant-based car, with a grille that widened at the bottom and extended under the headlight clusters much like the fullsize 1960 DeSoto, and taillights modeled off the Valiant/Lancer rear fender, but with three small lights in a row along the fender edge, paying homage to the traditional DeSoto three-light fin treatment. MT speculated that this new compact DeSoto would carry the name "Adventuress." While this would have made for a slick tie-in to the larger, sportier Adventurer, I doubt that with gender attitudes being what they were at the time DeSoto would have gone with something that overtly feminine. (Especially after the tiny number of Dodge LaFemmes sold just a few years earlier.)
Preproduction lead times (and the notable differences between the A and LA engines, particularly in regards to head and intake/exhaust system design) being what they are, development of the 273 would have had to start around 1959-60.
Aluminum engine blocks were seen as the Big New Thing in this era, and while many remember the Corvair's use of aluminum and the Buick/Olds/Pontiac aluminum-block 215 V8, few remember the brief production of aluminum blocks by manufacturers other than GM. Chrysler made an aluminum-block Slant Six as an option, apparently only in 225 configuration. It would be safe to assume that aluminum V8s were also under development, if for no other reason than to compete with GM.
|5.9 (360)||Ram 1500 and 2500, Van, Wagon||230@4,000||330@3200|
|5.9 (360)||Dodge Ram 3500||230@4,000||330@2,800|
|5.2 (318)||Dakota, Ram Van, Ram Wagon||220@4400||295@3200|
|5.2 (318)||Ram Pickup||220@4400||300@3200|
|3.9 V6||Dakota, Ram Van, Ram Wagon||175 @4800||225@3200|
|3.9 V6||Ram Pickup||175 @4800||230@3200|
Identifying LA Series V-8 engines and parts interchange
LA engines have the distributor at the rear, and the displacement is on the left front of the block, below the left cylinder head. LA valve covers are held on by five screws on the outside of the covers. If you remove the valve covers (the gaskets tend to go after 10-20 years), do not tighten these screws too far, and follow the instructions for 2.2 valve cover replacement in the FAQ. (But use a rubber gasket instead of RTV alone).
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 significantly reduced on replacement. Example: 1976 Plymouth Volare factory timing spec was 2 degrees (in Canada... was very snappy) and after I had changed the gaskets I found I couldn't make it ping even with as much as 10 degrees advance whereas 6 degrees was almost undriveable."
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 alot faster than a 318, or a 340."
Ed 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.
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.
Carl Payne: The main differences to the new 5.2l and the old 318 are in
the block and heads. The new block has roller lifters, with a new lifter angle, and has bosses for the lifter retainers.
The heads are high-swirl / high-flow heads, and the Magnum has a better intake. Some changes were made to commonize the 5.9, 5.2, and 3.9 V6 engines.
Gary Howell: "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."
Steve W. added, “LA rods are not interchangeable with Magnum pistons. I just learned this while attempting to hang some MP stroker 360/403 pistons onto 1986 360 LA rods. The big end of the LA rod is 1.20 inches wide, while the MP stroker piston I am using has a pin width of 1.16 inches measured with a digital caliper.”
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).
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|
- 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
Relevant LA V8 engine links
- LA predecessors: the A-engines
- Speaking to the engine architect: Willem Weertman
- About the engine architect: (Auto)Biography of Willem Weertman
- Speaking to an LA-engine engineer: Pete Hagenbuch
- Low-Buck Bolt-On Upgrades by Rick Ehrenberg
- V10 (truck version)
- The 3.9 liter V6: LA V6 engine (based on the 360)
- Upgrading your LA (273, 318, 360)
- Four-cylinder LA racing engine (no, that's not a typo!)
- 318 and 360 specifications for squad car use, 1967-1976
- Factory propane-powered 318 engines
- Repair tips
- Performance tips
- Allpar (Chrysler and Dodge enthusiast site)
- Mopar Engines
- The Valiant Pages
- How to Hot Rod LA Engines (318, 273, 340, 360, 1965 - 1989) - 20% off
to Hot Rod Small Block Mopar Engines : Covers All Chrysler, Dodge &
Plymouth LA Series Engines-1965 to Present-273-318-340-360 C.I.D. ~ Larry Shepard / Paperback / Published 1989 - Our Price: $14.36 ~
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- How to Rebuild Your Small Block Mopar ~ Taylor, et al / Paperback / Published 1982
Our Price: $14.36 ~
You Save: $3.59 (20%)
Chronology of the LA series Chrysler V8 engines
(Thanks to Stephen Havens)
- In 64 1/2 the 273 was released as a new lightweight compact V8 for the A-body, requiring notches in side of block to clear the power steering pump. It had 2bbl mechanical cam forged crank and 8.8:1 pistons.
- 1965 - 273 recieves more agressive cam and 4bbl with 10.5:1 pistons; these will remain through 1966.
- 1966 - bolt angle on the intake changes; 64 and 65 heads and intake are unique.
- 1967 - 318 released with hydraulic cam, forged crank, 2bbl carb, 9 : 1 pistons; truck motors recieve water heated intake with no exaust crossover.
- 1968 -
- 273 gets hydraulic cam and loses forged crank
- 4bbl 318 loses forged crank
- no more water heated intake on trucks
- 340 released with forged crank, 4bbl, hydraulic cam (in 1968, only the 4 speed cars got a more agressive cam in the 340, automatic cars got a cam that the next year would become standard in high performance small block mills). New heads, larger ports and valves first year for the dual plain intake 4bbl only.
- 1969 - last year for the 273
- 1970 - 340 gets Six-Pak, revised pushrod holes on these J heads for more meat in the intake runners. Also, T/A blocks with thicker webs for the ability to install 4 bolt mains on 2 3 and 4.
- 1971 - 360 released, 2bbl hydraulic cam, cast crank, J heads
- 1972 -
- 318 and 340 compression drops into the 8s
- 340 gets smaller valved J heads (previously all 340 except the six pack got X heads; Six=Pak J heads were machined for larger valves)
- 1973 - last year for 340, all 2bbl intakes become dual planes with EGR valves; before all intakes were single plane except 340 4bbl manifolds
- 1974 - 360 gets 340 cam carb and intake and is dubbed the E58 police engine. In 1975, the 360 is rated at 230 hp @ 4400 rpm, 300 lb-ft @ 3,600 rpm.
- 1977 - altitude-adjustable carburetors for Fury/Monaco and Aspen/Volare sold in high altitude locations; low-slip torque converter for TorqueFlite.
- 1978 - 318 gets 360 heads, cam, intake, and carb; the E48 is born. The 318 gets a lighter carburetor with “solid fuel metering” and the 360 gets additional throttle return springs. Second Generation Lean Burn debuts on both. California cars get a four-barrel 318. TorqueFlite gets lockup torque converter.
- 1979 — the 360 E58’s compression is dropped to 8.0:1 (from 8.4) and horsepower drops to 195 @ 4,000, with torque at 280 @ 2,400 rpm. The engine ceased car production in late 1980; in 1979 it was in the Volare, Aspen, Cordoba, Newport, and New Yorker. Mopar Performance releases “X block” for racers, which can be installed at 340 cubic inches or bored out to the recommended 355 cid (or further).
- 1983 - 318 police head released, larger than 360 combustion chamber, added water passages for cooling
- 1985 - Federal 318s went to a roller cam and lifters (unless they had the four-barrel carburetor), reducing friction and increasing longevity; valve shourding was used to increase the burn rate; and the compression ratio was hiked from 8.4:1 to 9.0:1. Truck engines did not get the roller tappets at this time, according to Chrysler’s literature of the day.
- 1986 - 318 receives high swirl heads
- 1987 - 3.9 is developed from 360
- 1988 - 318 get hydraulic roller cam; 3.9 and 318 get throttle-body fuel injection
- 1989 - 360 gets hydraulic roller cam
- 1990 - All LA engines get a new single-lip (using a spring) positive-construction valve stem seal; the 5.9 gets a new dual-lip rear crankshaft seal as well. Both seals are made of Viton®.
- 1991 - New head gasket for all LA engines; the new graphite-base, non-asbestos material resisted leaks better.
- 1992 - Magnum appears on 3.9 and 318 (5.2)
- 1993 - Magnum 360 (5.9) appears
- 1999 - 4.7 V-8, the LA family's replacement, appears on the Grand Cherokee, with slow phase-in planned for other models (including V-10 and possibly V-6 derivatives).
- 2002 - The 318 is gone, leaving the 360 as a high-power option on pickups until the Hemi is available. A larger Viper V-10 replaces the original.
- 2003 - Truck V-10 cancelled; Viper V-10 continues the LA design into 2004, and is used in the Ram SRT-10.
- 2007 - A new Viper V-10 will be introduced, worked over by McLaren.
- 2012 - The Viper V-10 is moderately upgraded