Detroit 671 Parts and Information

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Parts for Detroit Diesel 6-71

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Marine Engine Parts

At Diesel Pro, we have built our business around those who work in or around boats. So if you are looking specifically for marine parts, you have come to the right place. We specialize in providing parts for marine engines, especially the Detroit 671 (sometimes referred to as Gray Marine.) In other words, if you are the captain of a boat, or a marine mechanic, you have come to the right place. We offer many products that are essential, as well as a wide variety of products that commonly used on boats that aren't directly part of the engine, such as sirens, lights, and so on. You can also visit our 'Sea Water' option above to see impellers, heat exchangers, and water strainers, which are absolutely key to a boat engine running as smoothly as it should. To jump to a specific section, please select an option below:

See Impellers, Raw Water Pumps, Heat Exchangers and more

Marine Lights, Life Jackets, Sirens, Toilets

See 671 Two Valve Parts for Sale

See 671 Four Valve Natural Parts for Sale

See 671T (Turbo) Parts for Sale

Detroit Diesel 6-71 Engine Variants – Specifications & Applications

Overview

The Detroit Diesel 6-71 is one of the most recognizable diesel engines in the history of heavy equipment, transportation, and marine propulsion. Originally introduced in 1938 and refined over decades, this inline six-cylinder, two-stroke dieselengine remains relevant today, especially in the aftermarket for fleet restoration, repowers, and rebuilds. It has appeared in multiple configurations: the non-turbo 2-valve, the non-turbo 4-valve, and the turbocharged (6-71T) variant.

All three versions share the same displacement and general architecture but differ significantly in power output, airflow characteristics, and application focus. These differences affect everything from injector selection to cylinder head design and air handling.

At Diesel Pro Power, we support every version of the 6-71 engine with a full catalog of premium aftermarket parts, including overhaul kits, cylinder heads, turbochargers, blower components, and water pumps. This guide details each variant’s specifications and highlights the industries and equipment types that depend on them.

Detroit Diesel 6-71 Non-Turbo – 2-Valve Head Type

Technical Specifications

Engine Type: Inline six-cylinder, two-stroke diesel
Head Design: Two valves per cylinder (one intake, one exhaust)
Displacement: 426 cubic inches (6.99 liters)
Bore x Stroke: 4.25 in x 5.00 in
Compression Ratio: Approximately 17:1
Aspiration: Naturally aspirated via Roots blower only
Fuel System: Mechanical unit injectors
Governed Speed: 2,100 RPM
Horsepower Range: 165 to 210 HP @ 2,100 RPM
Peak Torque: 400 to 500 lb-ft @ 1,200 to 1,600 RPM
Oil Capacity: ~5 to 6 gallons
Coolant Capacity: ~4 to 5 gallons

The 2-valve 6-71 was the original configuration and remained in production for decades. Its airflow is limited by the valve count, making it best suited for low-load and steady-RPM applications.

Applications

Marine Industry

River workboats
Harbor service barges
Small ferries with minimal propulsion demands
Classic pleasure boats and converted tugboats

Industrial Applications

Stationary generator sets (prime or standby power)
Fire pumps and irrigation units
Light-duty compressors and small drilling equipment
Small airfield power units

Ground-Based Equipment

Graders and pavers (pre-1970s)
Utility trucks
Old crane carriers and material handlers
Military cargo trucks (WWII era)

Key Traits

Easy to service in remote environments
Lower cost due to simpler head design
Good fit for repower projects where maximum HP is not required
Long-lasting when used below rated capacity

Detroit Diesel 6-71 Non-Turbo – 4-Valve Head Type

Technical Specifications

Valve Configuration: Four valves per cylinder (two intake, two exhaust)
Aspiration: Roots blower (no turbo)
Horsepower Range: 210 to 238 HP @ 2,100 RPM
Torque: 475 to 525 lb-ft
Fuel System: Mechanical unit injectors
Compression Ratio: ~17:1
Other Specs: Displacement, oil capacity, and cooling system remain identical to 2-valve version

The 4-valve head enhances airflow and fuel burn efficiency, offering higher output without increasing displacement or requiring a turbocharger. This makes it a logical upgrade path or factory option for operations needing more power without added complexity.

Applications

Marine Use

Mid-size fishing vessels
Harbor pilot and inspection boats
Auxiliary drives on larger ships
Converted classic vessels requiring moderate HP increase

Commercial Equipment

Transit buses (especially GM or RTS platforms)
Cement mixers and dump trucks
Rail maintenance vehicles
High-torque portable pumps and compressor trailers

Key Traits

Enhanced airflow improves throttle response
Easier starting in cold conditions
Lower emissions compared to 2-valve
Factory-preferred for many post-1965 6-71 installations

Detroit Diesel 6-71 Turbocharged (6-71T)

Technical Specifications

Aspiration: Turbocharged with Roots blower assist
Head Configuration: Four valves per cylinder (required for turbo airflow)
Displacement: 426 cubic inches
Horsepower Range: 238 to 310 HP @ 2,100 RPM
Peak Torque: 550 to 675 lb-ft @ 1,200 to 1,600 RPM
Turbocharger Boost: 14 to 22 psi
Compression Ratio: 16.5:1 (slightly lower to accommodate boost pressure)
Fuel Injection: Matched to turbo output; typically larger injector sizes (e.g., N70 or N75)
Oil and Coolant Capacities: Same as naturally aspirated versions

The turbocharged 6-71 dramatically improves power output and efficiency, making it suitable for demanding environments, high-altitude performance, and dynamic throttle conditions. It is commonly referred to as the 6-71T and is instantly recognizable by the presence of the turbocharger mounted in conjunction with the Roots blower.

Applications

Marine Use

Fast fishing vessels and offshore patrol boats
Twin-engine sportfishing yachts
Turbo-upgraded shrimpers and scallopers
Ferries with time-sensitive docking routes
Crew boats for offshore oil platforms

Industrial Use

Large compressors for mining operations
Frac fluid power units
Fire engines and emergency pump platforms
Drilling rigs in oilfields and water wells
Heavy-load conveyors in quarries

On-Highway and Defense Use

Fire trucks and emergency response vehicles
Tank retrievers and tracked military equipment
Armored buses and homeland security vehicles
Vintage racing truck conversions

Key Traits

High horsepower-to-displacement ratio
Excellent for high-RPM loads and uphill demand
Better combustion efficiency and reduced black smoke
Requires more precise maintenance (especially on turbo and cooling systems)

Side-by-Side Comparison Table

Feature	6-71 Non-Turbo (2-Valve)	6-71 Non-Turbo (4-Valve)	6-71 Turbocharged (6-71T)
Valves per Cylinder	2	4	4
Aspiration Method	Blower only	Blower only	Turbo + Blower
Horsepower Range	165–210 HP	210–238 HP	238–310 HP
Torque Output	400–500 lb-ft	475–525 lb-ft	550–675 lb-ft
Fuel Efficiency	Basic	Improved	Superior under load
Maintenance Complexity	Low	Moderate	Higher (turbo maintenance)
Best For	Simplicity & Low RPM	Mid-power Steady Ops	Dynamic Load High Torque