1972 Plymouth Road Runner Engine Options and Specifications

In 1972 the Plymouth Road Runner could be ordered with three different engines.

For the 1972 Road Runner, the 400 4 barrel engine was the standard engine. Two engine options were available including the 340 4 barrel and the 440 4 barrel. If the 440 was ordered, the GTX name was added to the Road Runner calling it the Plymouth Road Runner GTX.

This article will include the 1972 Road Runner engine options and their specifications. This includes the engine code, cost, displacement, horsepower, torque, compression ratio, camshaft, lifter type, valve sizes, bore, stroke, air cleaner, exhaust, fuel and carburetion.

1972 Plymouth Road Runner Engine Options and Specifications

1972 Road Runner GTX with a 440.
1972 Road Runner GTX with a 440

The 1972 Road Runner came with the following engines.

  • 400 4-barrel (Standard)
  • 340 4 barrel (Optional)
  • 440 High Performance 4 barrel (Optional)

Originally another engine was planned for the 1972 Road Runner GTX. The second engine was the 440 Six Barrel. The ads, brochures and dealer information printed for 1972 indicated the 440 Six Barrel as an available engine option for the GTX. Please see the 1972 Road Runner GTX brochure in the photo below.

1972 Road Runner brochure indicating the 440 Six Barrel as a GTX option.
1972 Road Runner brochure indicating the 440 Six Barrel as a GTX option

The Six Barrel plans were quickly scrapped but not before a few of the cars were produced. We know of at least one GTX which is shown in the video near the end of this article.

The 426 Hemi engine was dropped and was not available for 1972. The 383 was also dropped for 1972 and was replaced by the 400 engine.

In 1972 manufacturers began rating horsepower and torque with net ratings.

1972 Gross to Net Horsepower and Torque Change

Prior to 1971 an engine’s gross horsepower and torque were used for the factory power ratings. In 1971, the manufacturers reported both gross and net horsepower and torque. Starting in 1972 SAE gross horsepower was no longer used and the SAE net horsepower became the new rating.

Gross and net horsepower are both measured at the crank. The difference is the use of engine accessories, air cleaner and factory exhaust to calculate net horsepower which is not used for gross horsepower.

Therefore, in addition to horsepower robbing internal engine changes, the net rating lowered the power numbers for 1972.

1972 Plymouth Road Runner With a 400 High Performance 4-barrel

400 4 barrel in a 1972 Road Runner
400 4 barrel in a 1972 Road Runner

The 400 4-barrel engine was the standard engine for the 1972 Plymouth Road Runner. It was the first year the engine was available for the Road Runner and replaced the 383 which was discontinued.

The 400 engine was essentially the same as a 383 with the same stroke but with a bigger bore size. The engine code is E68.

Let’s take a close look at the 400 4 barrel engine specifications.

Specifications400 4-barrel
Displacement400
Bore and Stroke4.342″ x 3.375″
Horsepower (Net) 255 @ 4,800 RPM
Torque (Net)340 @ 3,200 RPM
Compression Ratio8.2:1
CamshaftHigh lift, high performance
Cam Duration/Overlap268°/284°/46°
Cam Lift.450″/.464″
Lifter TypeHydraulic
Valve Diameter, Intake2.08″
Valve Diameter, Exhaust1.74″
CarburetionSingle 4-bbl
Air CleanerDual Snorkel
Exhaust SystemDual, low restriction
Fuel RecommendedRegular
1972 Plymouth Road Runner 400 4 barrel Specifications.

1972 Road Runner With a 340 4-barrel

The 340 4-barrel engine was available as an option for the 1972 Road Runner. The compression ratio was drastically reduced from 10.3:1 to 8.5:1.

The 1.88″ intake valves were smaller than the 2.02″ valves the year before.

The first 340s produced had a forged crankshaft. As of April 11, 1972 a cast crankshaft replaced the forged crankshaft starting with 340 engine serial number HM340R-3911-8000. In addition, a different damper and a torque converter and/or flywheel with special balance was used.

The engine code was E55. Let’s take a look at the specifications.

Specifications340 4-barrel
Displacement340
Bore and Stroke4.04″ x 3.31″
Horsepower240 @ 4,800 RPM
Torque290 @ 3,600 RPM
Compression Ratio8.5:1
CamshaftHigh lift, high performance
Cam Duration/Overlap268°/276°/44°
Cam Lift.429″/.444″
Lifter TypeHydraulic
Valve Diameter, Intake1.88″
Valve Diameter, Exhaust1.60″
CarburetionSingle Carter 4-bbl
Air CleanerUnsilenced
Exhaust SystemDual, low restriction
Fuel RecommendedRegular
1972 Plymouth Road Runner 340 4 barrel Specifications.

1972 Road Runner GTX With a 440 High Performance 4-barrel

1972 440 engine in a 1972 Road Runner GTX.
1972 440 engine in a 1972 Road Runner GTX

The 440 High Performance 4-barrel was available for the 1972 Road Runner GTX. The engine’s horsepower and torque were decreased from the previous year. Partly due to the net ratings and a decrease in compression ratio.

The 1972 compression ratio decreased from 9.7:1 to 8.2:1 from the previous year. Also, there was a slight change for the camshaft exhaust lift. Another change was the carburetor brand which switched from Carter to Holley.

The engine code was 86. Let’s take a look at the specifications.

Specifications440 4-barrel
Displacement440
Bore and Stroke4.32″ x 3.75″
Horsepower (Net)280 @ 4,800 RPM
Torque (Net)375 @ 3,200 RPM
Compression Ratio8.2:1
CamshaftHigh lift, long duration, high overlap
Cam Duration/Overlap268°/284°/46°
Cam Lift.450″/.464″
Lifter TypeHydraulic
Valve Diameter, Intake2.08″
Valve Diameter, Exhaust1.74″
CarburetionSingle Holley 4-bbl
Air CleanerDual Snorkel
Exhaust SystemDual, low restriction
Fuel RecommendedRegular
1972 Plymouth Road Runner GTX 440 4 barrel High Performance Specifications.

1972 Road Runner GTX With a 440 6-barrel

The 440 Six Barrel was only available as an option for the 1972 Road Runner GTX prior to the production start of the year. As stated earlier, at least one GTX snuck out of the factory with the Six Barrel engine.

It appears almost all the engine specifications remained the same from 1971 to 1972. There was a slight change with the camshaft exhaust lift.

The engine code was E87. Let’s take a look at the specifications.

Specifications440 Six Barrel
Displacement440
Bore and Stroke4.32″ x 3.75″
Horsepower (Net)330 @ 4,700 RPM
Torque (Net)410 @ 3,200 RPM
Compression Ratio10.3:1
CamshaftHigh lift, long duration, high overlap
Cam Duration/Overlap268°/284°/46°
Cam Lift.450″/.464″
Lifter TypeHydraulic
Valve Diameter, Intake2.08″
Valve Diameter, Exhaust1.74″
CarburetionTriple Holley 2-bbl
Air CleanerUnsilenced
Exhaust SystemDual, low restriction
Fuel RecommendedPremium
1972 Plymouth Road Runner GTX 440 Six Barrel High Performance Specifications.

That’s the complete list of engines available for the 1972 Plymouth Road Runner. If you have any questions to ask me about the engine options or specifications for the 1972 Road Runner car model, send us an email found specifically on my contact page or comment below.

1972 Road Runner GTX with a 440 Six Barrel engine.

About 38 years ago I assembled my first Mopar engine, it was for a 1970 ‘Cuda. It’s at that time my hands on experience with Mopar cars and engines, including the 440, started. Although my research of the engines started years earlier.

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