Mopar 340: Evolving Legacy Of Ultimate Power

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If you owned a Mopar in the late sixties, it wasn’t just big blocks that were having fun on the streets. The Mopar small-block 340 had a serious attitude.

The 5.6L (340 ci) engine was a part of the LA family of small block engines Chrysler produced from 1968 - ‘73. The engine produced significant power, 275 hp (although most feel that was likely understated). The compression ratio was 10.5:1, making the engine perfect for racing or the street.

If you lived in the late sixties, you probably remember the muscle cars everyone seemed to be driving. While the Richie Rich’s of the land had parents who could afford the big block engines like the 426 Hemi, most of us average Joes had to settle for small blocks. And while that might seem like a sad tale, trust me, it wasn’t. Because in the late sixties, and early seventies, the one car that your Ford buddy didn’t want to pull up next to was any car with a Mopar 340. Why? Because in its day, the 5.6L baby block could blow the socks off of any Ford or Chevy. The engine wasn’t just small. It was powerfully small. Put a Mopar small block into a lightweight mid-sized car, load it up with some heavy carburation, tune it just right, and you could smoke the tires down the block. The 340 could fly. The fact that many young buyers were pulling their 318s out and swapping them with the 340 made them even more popular. So in honor of this small block with serious street cred, we thought we’d look back at the days when a small-block Mopar could be the king of the street.

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A Motor For The Masses

The Mopar 340 was introduced in 1968 as an update to the Chrysler LA 318, the standard engine for much of the lineup since 1964. Attempting to capitalize on the growing popularity of racing (both stock car and drag racing), the company wanted a high-performance engine that could be as versatile as possible for young buyers who needed to drive on the street during the weekday but wanted to take their cars racing on Saturday night.

The engine was part of the LA family (meaning “Light - A” to distinguish the engine's weight reduction from many of the older Poly A motors used in the fifties). The new LA engine family was about fifty pounds lighter, more compact, and provided better power. The result of these lean engines is that they could be put into smaller vehicles, making them go very fast.

The Mopar Runs With Ford And Chevy

When the engine rolled off the factory line in 1968, the company reported that the 5.6L V8 produced 275 hp, but most historians and classic car lovers think that was grossly misleading. (Many people believe that Chrysler misrepresented the power output to help ease insurance fears so that companies would not have an excuse to raise premiums on young drivers. But it also helped to ease parents' fears about the car’s speed as their kids ventured out on the weekends).

With an engine designed for performance at a 10.5:1 compression ratio, the little Mopar tended to have impressive runs. Young owners were delighted when they discovered that their new 340 Mopar could run a 0 - 60 mph time in close to six seconds. (The time for a ‘68 Ford Mustang was nearly equal at 5.9 seconds, and the ‘68 Camaro with a 396 ran a 6-second 0 - 60 time).

Dodge took advantage of the speed of the new LA engine in their advertising. A sales brochure from 1970 extolled the Dodge Swinger 340 as a full-fledged member of the “Scat Pack.” The 340 was the only small block invited to the big boy's party.

This Is Not A Stroked-Out 318

There is a misconception that the Mopar 340 small block was just a bored-out version of the LA 318 engine, but that is not the case. While the two engines share the same cast iron engine block and stroke, they are very different inside.

Tom Hoover (the father of the Hemi) led Chrysler engineers to design a motor that could withstand the rigors of racing. To reinforce the stability of the engine, the 340 uses forged shot peen crankshafts, steel connecting rods, and high-compression aluminum pistons with modified cylinder heads. In addition, the intake and exhaust valves were significantly more prominent on the 340 (2.02-inch intake valves and 1.60 exhaust valves), which allowed for better airflow. (The larger valves created an issue for the spark plugs, which had to be recessed farther out to fit).

The 340 came standard with a four-bbl carburetor with a dual-plane intake manifold. (The 318 had one two-barrel carburetor with a single-plane setup). There were other heavy-duty components, like a double-row roller timing chain, which engineers felt would help with valvetrain control.

The 340 Gets a Six-Pack

The engine stayed primarily intact for the first two years of production, but in 1970, Chrysler added a Six-Pack carburetion to their engines. (This unique option consisted of 3 double barrel carburetors mounted to an aluminum Edelbrock intake manifold. The new configuration also required a revised valve cover because it interfered with the spark plug wires.

The new configuration was only offered on two models: the Dodge Challenger T/A and the ‘Cuda AAR. To accommodate the new carburation required modified valve covers. The Six-Pack pushed the power output rating to 290 hp and 340 lb-ft of torque, but the results were mixed (the new power outputs didn’t translate into sales - 2.935 Challengers and 2,734 AARs). By 1971, the six-pack was no longer an option for the 340, although it was offered for the larger big block motor, the 440 V8. (The 426 Hemi never came from the factory with the six-barrel setup. Instead, it had dual 4-bbl Carter AFM carbs).

The Mighty Mopar Cuts Clipped

The following year (1972), the Government forced every car company to make drastic changes to their lineups to meet stricter emissions standards. Chrysler was forced to drop the Hemi engine (it was just too expensive to build, customers didn’t want to pay extra to have it, and it would have had to be revamped to meet the new regulations). Chrysler decided to shrink the valves, use a cast iron crank, and “detune” the power output of the 340, which now had a compression ratio of 8.5:1 and a much lower horsepower rating of only 240.

Before long, sales made it clear that America’s fascination with speed and performance was drawing to an end. Consumers began to drift away from the inefficient gas-guzzling engines they loved and began focusing on less-powered vehicles with better fuel economy. When the oil embargo hit in 1973, the 340 had run its course and bowed out of the scene without fanfare. The engine was replaced in 1974 with the 360 V8, which produced 245 hp and, at the time, was the most potent engine Mopar was making.

What Are The Specs Of The 340 Engine?

The following list contains specifications on the 340 as it was produced in 1968 - 69.

Mopar 5.6L 340 ci V8 Engine Specifications
Production 1968 - ‘73
Displacement 5.6L (340 cubic inches)
Configuration Naturally Aspirated
Horsepower 275 hp (as reported)
Torque 340 lb-ft
Bore 4.02 inches
Stroke 3.75 inches
Bore Spacing 4.04 inches
Intake Valve 2.02 inches
Exhaust Valve 1.60 inches
Compression Ratio 10.5:1 (1968 -71 model year)
8.5L1 (1972 - ‘73 model year)
Firing Order 1-8-4-3-6-5-7-2

The 340 Mopar Today

There is a good market for the 340 today with plenty of aftermarket support should you decide to do a restoration project. According to Jegs Performance, you should expect to pay between $5,000 - $8,000 for a 340 crate engine. Restorers should note that the 340 was only built for a few short years, so the availability of these engines is at a premium. (If you find a 340 at a reasonable price, it is best to jump on it - just saying).

What Is The Value Of A Muscle Car With A 340?

Depending on the car, a typical muscle car like a 70 Dodge Dart GTS is around $22,600, according to Hagerty. While that is not nearly the amount that a 426 Hemi might bring, it does mean that owning a piece of Mopar history is easier than you think. (We suspect that since Dodge has announced the end of the Hemi engine, as they move to electric vehicles, any piece of the “Scat Pak” will continue to grow in value.