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Valiant V8 engines: 273, 318, 340, and 360

la 318In the United States, where only the V8 was considered to be capable of any performance, the Valiant quickly gained a small V8 engine designed with the small car in mind — the 273 V8. This engine was based on the existing A-series V8 engines, but was considerably lighter, hence the designation LA — Lightweight A. In Australia, where the Hemi Six could beat Ford’s big V8s and where gasoline was somewhat pricier, Chrysler’s V8s were used more for luxury than sheer performance.

The LA engines were efficient and durable designs that remained in use in the United States into the 21st Century, with one version — a V10 — used in the company’s fastest car, the Dodge Viper.

Engine Years (USA)* Stroke Bore Horsepower ratings before 1971 were taken without accessories (“gross” vs “net”). Ratings after 1971 are SAE standard and are considerably lower for the exact same engine.
273 1964-69 3.31 3.63
318 (5.2) 1967-2002 3.31 3.91
340 1968-73 3.31 4.04
360 (5.9) 1971-2002 3.58 4.00

The following are some consolidated specifications for Valiant, Charger, Pacer, Duster, Dart, etc. engines:

USA specifications 273 V8 318 V8 340 V8
Gross horsepower, 1968 190 @ 4400 230 @ 4400 275 @ 5000
Gross horsepower, 1972, Australia   230 @ 4,800 275 @ 5,000
Net horsepower, 1973 (not made) 150 @ 4,000 240 @ 4,800
Torque, lbs.-ft., 1968-1972 (US, AU) 260 at 2000 340 at 2400 340 at 3200
Compression ratio, 1968-72 (US, AU) 9.0 to 1 9.2 to 1 10.5 to 1
Compression ratio, 1973   8.6 to 1 8.5 to 1
Bore, inches 3.63 3.91 4.04
Stroke, inches 3.312 3.312 3.312
Displacement, cu. In. 273 318 340
Carburetor type (1968-73) 2-bbl. 2-bbl. 4-bbl.
Air cleaner type Silenced Silenced Unsilenced
Exhaust Single Single Dual
Camshaft Standard Standard Special
Fuel Regular Regular Premium

273 V8

273 mopar - chrysler engineThe first LA was the 273, with a two barrel carb, producing 180 gross hp. Introduced to Americans in 1964, it had a thin-wall casting and simpler wedge-heads and valves, which saved around 50 pounds over the existing A-series V8. The 273 ended up being only fifty pounds heavier than the 225-cid slant six. 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.

Engine designer Willem Weertman said:

When it came to the LA engine we made all the valves tipped to the intake manifold and inline as viewed from the front of the engine giving it a wedge shaped combustion chamber.  The reason we went to such a change, which triggered totally new cylinder heads and manifolds for the engine was that the engine was designed to go into the Valiant car.  The Valiant car was originally not designed to take a V-8 engine.  So we were really limited in every which way about getting the engine in place and the older A engine was simply far too wide at the cylinder heads in order to go into the car. So we put the wedge head engine, cylinder heads on top of the A engine and that was what we needed to do in order to get that engine into the Valiant. 

In the process we also wanted to take a lot of weight out because the Valiant ... wanted to have engines much lighter than what a conventional A engine would be.  So we took as much as we could out of the cylinder heads and the intake manifold and the cylinder block which is of course the largest and heaviest piece of an engine.  That triggered a new casting process for the cylinder block that allowed us to make all the walls thinner and we took a lot of the weight out of the block.  ... From going from our polyspherical chambers to the inline valve wedge chambers we found it was a wash.  There was concern that it would be a loss but it was not.

1967 specifications 273 V8 273 V8
Carburetor 2 barrel 4 barrel
Manual transmissions 3 or 4 speeds 4 speeds
Gross horsepower 180 @ 4,200 235 @ 5,200
Torque 260 @ 1,600 260 @ 4,000
Compression Ratio :1 8.8 10.5

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.)

In 1968, the 273 got a hydraulic cam; the forged steel crank was replaced with a standard nodular cast iron crankshaft to save money (the 318 also used the iron crank). 1969 was the final year for the 273, its thunder having been stolen by the 318, which was introduced in 1967. The 273 predated hardened (for unleaded fuel) valve seats.

318 V8

The 318 (5.2 liters) was brought out in 1967; the main difference from the 273 was its larger 3.91” bore. The 318 was never used as a performance engine by Chrysler; the 273 four-barrel matched it in peak horsepower, and the more performance-oriented 340 was quickly released in 1968. It had hydraulic tappets from the start, but hardened valve seats were not used until at least 1973.

The 318 was used as a police engine, mainly in the M-bodies (Diplomats and Gran Furys); it was, in most years, the largest engine available in four-door Valiants. With the 340 and 360 around, the 318 kept its "economy carb" from 1968 through 1978, when it got a four-barrel option to make performance acceptable with California emissions systems.

 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

Starting in the mid-1970s, exhaust-valve seats were induction-hardened for lead-free fuels. In the hardening process, seats reached a temperature of 1700°F and were allowed to air-cool, hardening the valve­seat surfaces to a depth of .05" to .08". The exhaust-valve stems were chrome-plated for increased resistance to wear.

Starting in the mid-1970s, 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. Electronic Lean Burn was standard in the U.S. and Australia by the late 1970s.

The 1978 carburetor was over a half pound lighter than the previous carburetor, and was designed for solid-fuel operation: a solid, continuous stream of fuel was fed to the primary discharge nozzles by the metering system. The fuel was mixed with air upon entering the nozzles.

318 Engine Troubleshooting

Duane D. Hughes wrote:

A couple of tips for 318s with Carter 2 bbl carbs:

Chrylser Engines 1922-1998 Willem WeertmanMine was a 1976, and it stumbled and sagged badly from the time it was started until it was fully warmed up It did this from the time it was new. This is a classic sign of a too lean mixture. I happened to have a friend who worked in the service department of a Dodge dealer, and he advised me to raise the metering rods about 1/16 th of an inch. This can be done without disassembling the carb. Just add the additional 1/16th inch rise, and you'll cure your problem. I did this on my car, my dad's 1976, and my uncle's 1977. Worked in every case.

Another problem I had with that car was pinging at light, not heavy load. It would ping on the slightest grade at highway speeds. One day I happened to 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. I fooled around with various Allen head wrenches until I found one that seemed to grab something. Sure enough, 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)

Curt Pinck wrote: It is interesting the wide variety of timing specs given for the 318, all the way from 2 degrees ATDC to 16 degrees ATDC, depending on the type of engine and vehicle...Most books recommend not to try to time by ear, even if you have experience doing this.

Ted Devey adds two more steps:

  1. 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.
  2. Several years ago I dismantled the Carter 2-barrel carburettor and reassembled it with the jet assembly upside down. There is no obvious wrong way.

The 340: high performance in a small package

chrysler 340 V8 engineOne of the best engines of the 1960s and 1970s for performance enthusiasts was the 340 V-8. It had high-flow heads, big ports, a two-level intake manifold, and a six-barrel option (three two-barrel carbs). The package allowed for high speed with the light weight helping handling. The 340 cars gave away nothing to the 383 cars in a straight line, and were ahead of the 383 cars on anything involving turns — and spark plug access.

When the 340 came out in late 1967, it was a street fighter from the start. Separating the 340 from the 318 were:

1970-71 engines were painted orange; they changed to blue in 1972-73, although some late 1971 engines ended up blue also.

The 340’s best power rating was 290 horsepower; even in 1973, it still managed 240-245 net horsepower. In 1971, the 340 came with the J heads and 2.02/1.60 valves. Since 1971 saw the introduction of the "360 style" J head, they used the same casting for 1971 340s and 360s, with different machining for the different sized valves. The 360 head actually saw first limited use in the 1970 340 Six-Pack AAR/TA, which also had 2.20/1.60 machined heads.

Pete Hagenbuch wrote: I drove a 1972 Road Runner with the 340 for a year. For driving pleasure that was my favorite muscle car. With anti-sway bars front and rear, the car was as light on its feet as most sports cars. My commute was a joyful dash in that car.

My 1971 Duster 340 was a bear in a straight line but try a little throttle in a turn and wheelhop off the road. I pulled out to pass a slow guy going about 40 on my way to work on a narrow two-lane road without much in the way of shoulders. Did a 3-1 kickdown, hit a bump, and ended up looking him right in the eyes!

In 1972, the 340 was seriously detuned, ostensibly for emissions reasons (but possibly also for insurance reasons). It went from a 10.4:1 to a 8.5:1 compression ratio, got smaller intake valves, and seriously fell in performance. 1973 was its last model year.

Parts from the 340 were transferred to a muscle version of the 360 in 1974. The high performance (HP) 360 went on to appear in A-body and F-body police cars, as well as the Little Red Truck and other fast pickups.

Micomlar wrote: “The windage trays supposedly resulted in an approximately 650 to 800 fouth gear top end finish improvement. These trays were also suspected to cause engine damage as they starved some critical bottom end components unless the engine was in peak mechanical shape. I own 3 340s (In a 1972 Challenger, a 1969 Dart and a 1973 Duster) and all 3 had the trays when I rebuilt them. One engine has genuine X heads and the other two have AAWJ 360 with the 1.88 intakes removed and the 2.02 stainless valves and the intake runners worked to match the larger foot print X head gasket outline. By increasing the intake valves and opening up the intake runners, the magic reported answer to the question of how much improvement is approximately 35 ponies.”

The 360

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"). To save money, the engineers cleverly gave the 360 the same connecting rods as the 318 — but changed the pistons and crankshaft to increase the combustion area. This threw the engine out of balance, so offset weights were added to both ends of the crankshaft assembly and to the vibration damper.

The 360 was relatively tame through 1974, when it received some 340 performance parts and a four-barrel carb in an effort to replace the 340 as a performance engine.

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.

The 1978 California version came with an air pump, which could be ordered elsewhere with the N96 emissions control package.

Across-engine specifications (United States, 1978)

1978 chrysler engine lineup

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."

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.

LA Series Components

(Thanks to Stephen Havens)

Valve sizes


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
273 4 barrel Mechanical 415/425 248/248
318 2 barrel 67 Hydraulic 390/390 244/244
318 2 barrel through 88 Hydraulic 373/400 240/248
318 4 barrel Hydraulic 430/444 268/276
318 roller cam Hydraulic 391/391 240/240
340 4 barrel 68 man trans Hydraulic 444/453 276/284
340 4 barrel Hydraulic 430/444 268/276
340 70 six pak Hydraulic 430/444 268/276 (adjustable rockers)
360 2 barrel 71-74 Hydraulic 410/412 252/256
360 2bb 75-up Hydraulic 410/410 252/252
360 4 barrel Hydraulic 430/444 268/276

Carburetors (U.S.)

Relevant LA V8 engine links 

Chronology of the LA series Chrysler V8 engines through 1983

(Thanks to Stephen Havens)

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