For factory performance, the Mopar 340’s strongest years are generally 1968–70, with 1970’s special six-pack version in a category of its own; 1971 remains a strong choice in four-barrel form. The weakest years are 1972–73, when lower compression and less aggressive components reduced performance. This is a performance-focused ranking, not a verdict on durability or every surviving engine’s condition.
How to judge the 340’s best and worst years
Compare factory engine specifications and configuration, not just advertised horsepower or a car’s quarter-mile time. In 1972, manufacturers shifted from gross to net horsepower ratings, so the later rating cannot be compared directly with earlier gross figures. Vehicle tests also reflect the whole car—including its weight, transmission, axle ratio, condition and modifications—not the engine alone.
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The 340 arrived for 1968 Dodge Dart and Plymouth Barracuda applications as a high-output passenger-car engine developed from the 273. Chrysler’s SAE technical-paper abstract describes it as approximately the same size and weight as the 273 four-barrel predecessor: SAE International’s paper abstract.
Best years: 1968–71
1968: the strong debut
The first-year 340 established the engine’s performance reputation in the Dart and Barracuda. It belongs among the best years for someone seeking an early factory 340, though the available evidence does not establish a unique engineering advantage over 1969 or the regular four-barrel 1970 engine.
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1969: a strong continuation
1969 is part of the 340’s strong early period, but it is not possible to rank it decisively above 1968 or 1970 on the documented specifications here. MotorTrend reports approximately 20,000 Swinger 340s sold for the year; that figure indicates the model’s reach, not a performance advantage: MotorTrend’s history of the 1970 Duster 340.
1970: the standout six-pack, plus a strong four-barrel
The special 1970 340 six-pack is the year’s defining configuration. Built for the AAR ’Cuda and Challenger T/A, it used three two-barrel carburetors and should not be confused with the regular four-barrel 340. The special version makes 1970 the most distinctive year for factory performance, but it does not mean every 1970 340 had six-pack equipment. MotorTrend also reports nearly 25,000 Duster 340s sold for 1970; that is a model-sales figure, not a count of six-pack engines.
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Keep the six-pack’s advertised rating separate from secondary reports of dynamometer testing. Those reports are not a substitute for a verified factory rating or a year-to-year test under controlled, comparable conditions. SlashGear discusses the configuration and reported output: SlashGear’s account of the 340 six-pack.
1971: a strong four-barrel option
The 1971 Demon 340 shows that the engine remained a serious performance choice after the six-pack’s special 1970 application. Dodge gives the Demon’s rating as 275 hp and lists performance hardware including a forged-steel crankshaft, high-flow heads and high-load valve springs: Dodge’s 1970–1979 history.
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Dodge also recounts a Car Craft Magazine test from its April 1971 issue: a stock four-speed 1971 Demon 340 with a 3.91 axle ratio ran 14.41 seconds at 98.69 mph at Lions drag strip. MotorTrend separately reports 14.49 seconds at 98.25 mph in a January 1971 comparison test. These are period results for complete cars with their particular setups, not engine-only measurements or directly interchangeable ratings: MotorTrend’s historical account.
Weakest years: 1972–73
1972: the clearest performance step down
The 1972 Demon 340’s stated rating fell to 240 hp, and Dodge specifies 8.5:1 compression and 360 heads with smaller intake valves. The 240-hp figure is a net rating; earlier advertised figures generally used gross ratings, so the numerical difference alone overstates how cleanly the two eras can be compared. MotorTrend additionally reports a milder cam and a midyear change from a forged to a cast crankshaft. Taken together, the reduced compression and less performance-oriented specification make 1972 the clearest low point for stock performance in the 340’s run.
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1973: the final year
The 340 continued into the 1973 model year, with the lower-compression later-engine context continuing. Dodge had dropped the Demon name, and some 340-equipped cars carried the Dart Sport name instead. The 360 took the 340’s place after 1973. MotorTrend covers the engine’s later development and model context: MotorTrend’s 340 history.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Year-by-year snapshot
| Model year | What stands out | Performance assessment |
|---|---|---|
| 1968 | First year in Dart and Barracuda applications; high-output engine derived from the 273 | Strong early year |
| 1969 | Strong continuation; no established unique advantage over 1968 or 1970 | Strong early year |
| 1970 | Special three-carburetor six-pack for AAR ’Cuda and Challenger T/A, alongside regular four-barrel versions | Standout year, especially in six-pack form |
| 1971 | Demon 340 rated at 275 hp by Dodge, with performance hardware | Strong four-barrel year |
| 1972 | 8.5:1 compression; smaller intake valves; milder cam reported; midyear crankshaft change reported | Clear step down; 240-hp net rating for Demon 340 |
| 1973 | Final 340 model year; some Dodge applications called Dart Sport | Later, lower-compression context |
Which 340 year should a buyer or restorer choose?
For the strongest stock-performance case
Look first at 1968–71 four-barrel engines, or a genuine 1970 six-pack application if that specialized factory configuration is the goal. Within that range, condition and originality matter: a worn or modified example may not deliver the performance implied by its model year.
For authenticity and restoration
Choose the engine and components that match the car’s model year and original configuration rather than treating all 340s as interchangeable. The six-pack is a distinct 1970 setup, and the later 1972–73 specifications differ from the earlier performance-oriented versions. Confirm component identity against authoritative documentation for the specific car before buying parts.
For interpreting track times
Use period elapsed times as evidence about a particular car, not as a ranking of bare engines. Transmission, axle ratio, vehicle weight, tire and mechanical condition can change the result substantially. Dodge’s 1971 Demon test, for example, specifies a four-speed and 3.91 axle ratio; those details are part of the result, not incidental footnotes.
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