340 4-barrel
1968–1973High-performance factory small-block
Core 340 performance package
Mopar 340 LA V8 enginePhoto: Triple-green · CC BY-SA 2.0
Mopar · LA Small-Block
Mopar 340 LA V8
Chrysler's high-winding muscle-era small-block and one of the most desirable LA engines.
340
Cubic inches
The 340 combined a large 4.04-inch bore with the LA family's short 3.31-inch stroke, creating a responsive small-block that earned a performance reputation out of proportion to its displacement.
Key variants
All variants340 4-barrel340 Six Pack / Six Barrel
Displacement
340 ci
Bore
4.04"
Stroke
3.31"
Years
1968–1973
Key Takeaway
The 340 combined a large 4.04-inch bore with the LA family's short 3.31-inch stroke. That oversquare geometry supported larger valves and strong cylinder-head airflow, giving the engine a much more performance-oriented character than the 318.
Technical Specifications
- Compression
- 10.5:1 representative 1968 specification; reduced in later production years
- Horsepower
- Muscle-era ratings varied by year; high-performance factory combinations
- Torque
- 340 lb-ft @ 3200 rpm representative 1968–71 rating
- Architecture
- 90-degree OHV V8
- Block
- Cast iron
- Cylinder heads
- Cast iron
- Valvetrain
- Pushrod OHV, 2 valves per cylinder
- Aspiration
- Naturally aspirated
- Fuel delivery
- Carbureted; four-barrel and Six Pack performance combinations
- Firing order
- 1-8-4-3-6-5-7-2
The 340 combined a large 4.04-inch bore with the LA family's short 3.31-inch stroke. That oversquare geometry supported larger valves and strong cylinder-head airflow, giving the engine a much more performance-oriented character than the 318.
Internal Specifications
Variant-specific values are labeled. Engine families that span multiple years or RPOs can have different heads, cams, induction and rotating parts, so the exact code/year always takes priority.
Identification & Output
- Engine codes / RPO
- E55 (340 4-barrel; also used on some 1970 Six Barrel package records), E56 (340 Six Barrel/Six Pack reference), E58 (340 high-performance/police reference in some applications)
- Casting numbers
- 2780930 (1968–73 340 LA standard block reference), 3577130TA (1970–71 T/A and AAR 340 reference)
- Power rating
- SAE gross for 1968–1971; SAE net for 1972–1973
- Horsepower RPM
- 275 hp @ 5000 rpm representative 1968–71 rating (SAE gross)
- Torque RPM
- 340 lb-ft @ 3200 rpm representative 1968–71 rating
Operating Specs
- Production notes
- The 340 was Chrysler’s purpose-built high-performance LA small-block. The 1970 Six Pack/Six Barrel version supported the Challenger T/A and AAR ’Cuda Trans-Am homologation program.
Compatibility Notes
- 340 external balance and rotating-assembly details changed late in production; verify crank, damper and flywheel/flexplate before mixing parts.
- T/A/AAR blocks and heads have application-specific details; a casting number should be checked together with date codes and machined features.
Notable Applications
Dodge Dart GTS / SwingerPlymouth 'CudaPlymouth Duster 340Dodge Challenger T/APlymouth AAR 'Cuda
Strengths
- Large bore supports strong cylinder-head airflow
- Short stroke and performance-oriented factory hardware
- Excellent period-correct muscle-car pedigree
Weaknesses / Watch-outs
- Original blocks and heads command collector pricing
- Later low-compression versions differ from early performance combinations
Common Upgrades
- Modern aluminum cylinder heads
- Hydraulic roller or modern flat-tappet camshaft
- Improved intake and exhaust
Racing History & Legacy
The 340 Six Pack was central to Chrysler's 1970 Trans-Am homologation-era Challenger T/A and AAR 'Cuda program, while production 340 cars became staples of drag racing and street performance.
Among classic Mopar small-blocks, the 340 remains the benchmark for factory performance character.
References & Image Credit
Engine image: Triple-green · CC BY-SA 2.0 · source
Stellantis Mopar Nationals — 340 Six Pack Challenger T/A
manufacturer history
MaxWedge — Chrysler/Mopar engine bore and stroke reference
specialist technical reference
Mopar Enthusiast Network — 1966–1974 engine specification chart
historical specification
Mopar Performance electronic ignition instructions — Chrysler V8 firing order
manufacturer instruction
Mopar engine block casting-number reference
specialist reference
1969–1974 Mopar body-data-tag engine code reference
historical code reference
MotorTrend — Dodge Dart/Demon/Duster 340 history and specifications
historical specification
Key Factory / Build Variants
340 Six Pack / Six Barrel
1970Three 2-barrel induction
Homologation-era Challenger T/A and AAR ’Cuda version
Engineering Notes Worth Knowing
01
340 cu in / 5.6 L with 4.04 x 3.31-inch bore and stroke.
02
90-degree OHV LA-family V8.
03
Representative early compression was about 10.5:1, with later versions reduced.
04
Factory torque was about 340 lb-ft in representative 1968–71 specifications.
History · context · related reading
The Story Behind Mopar 340 LA V8
The 340 was designed as a performance small-block from the start. Its big bore, short stroke, and aggressive factory combinations made it the engine that proved Mopar did not need a big-block to build a serious muscle car.
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