Parts for Detroit Diesel 671 Non-Turbo - (4 Valve Head Type)

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Detroit Diesel 6-71 Non-Turbo – 4-Valve Head Type – Engine Specifications & Applications

Overview

The Detroit Diesel 6-71 Non-Turbo with 4-valve head is a refined version of one of the most trusted diesel engines in the world. As a member of the Series 71 family, the 6-71 inline six-cylinder engine has served in nearly every industrial, marine, military, and commercial application imaginable. The 4-valve head version, while still naturally aspirated via a Roots blower, provides a significant performance improvement over the older 2-valve design—offering enhanced airflow, better combustion, improved fuel economy, and cleaner operation.

At Diesel Pro Power, we provide full aftermarket support for the Detroit 6-71 4-valve non-turbo engine, including overhaul kits, cylinder heads, injectors, water pumps, gaskets, fuel system parts, and cooling system components. This guide presents in-depth technical specifications and a breakdown of real-world applications where the 6-71 non-turbo 4-valve engine continues to perform reliably.

Engine Specifications – Detroit Diesel 6-71 Non-Turbo, 4-Valve Head

Core Engine Architecture

Engine Type: Two-stroke inline diesel
Number of Cylinders: 6
Displacement: 426 cubic inches (6.99 liters)
Bore x Stroke: 4.25 in x 5.00 in (108 mm x 127 mm)
Aspiration: Roots-type blower (no turbocharger)
Cylinder Head: 4 valves per cylinder (2 intake, 2 exhaust)
Compression Ratio: Approximately 17:1
Crankshaft Bearings: 7 main bearings
Firing Order: 1-5-3-6-2-4
Rotation Options: Standard or opposite rotation (marine variants)
Dry Weight: ~2,150 to 2,350 lbs depending on configuration

This engine uses a Roots blower for forced induction, enabling it to function as a naturally aspirated system while maintaining consistent airflow through its 4-valve-per-cylinder configuration. The 4-valve head provides greater volumetric efficiency than the earlier 2-valve version, especially at higher RPMs.

Fuel and Air Management

Fuel System: Mechanical unit injectors (one per cylinder)
Injector Sizes: Typically N60 or N65 for 4-valve setups
Fuel Consumption: ~0.44 lb/HP/hr under load
Governor Type: Variable or fixed-speed mechanical governors
Air Intake: Blower-charged intake through dual intake ports
Valve Train: Pushrod actuated, overhead valve design with four valves per cylinder
Intake/Exhaust Flow: Cross-flow design for efficient scavenging

The 4-valve layout offers better cylinder filling and exhaust evacuation, leading to increased horsepower and torque, improved fuel efficiency, and more complete combustion compared to the 2-valve variant.

Power and Performance Ratings

Horsepower Range: 210 to 238 HP @ 2,100 RPM
Peak Torque: 475 to 525 lb-ft @ 1,200 to 1,600 RPM
Rated Speed: 2,100 RPM (adjustable to 2,300 RPM with governor modifications)
Idle Speed: 600–650 RPM
Air-to-Fuel Ratio: ~18:1

The 6-71 with 4-valve head delivers performance close to that of early turbocharged models, without requiring a turbo. This makes it a popular option for operators who want a non-turbo solution with enhanced output and reliability.

Lubrication and Cooling System

Oil Type: SAE 40 (preferred), or 15W-40 multigrade for wide temperature swings
Oil Capacity: Approximately 5.5 to 6 gallons (20.8 to 22.7 liters)
Oil Pressure (Normal): 40 to 60 psi
Cooling System Type: Water-cooled block with heat exchanger or direct keel cooling
Coolant Capacity: 4 to 5 gallons (15 to 19 liters)
Water Pump: Gear-driven centrifugal pump
Operating Temperature: 170°F to 190°F (regulated by thermostats)

This configuration is particularly reliable in marine and stationary industrial environments, where consistent temperature and lubrication are critical for long hours of operation.

Applications of the Detroit Diesel 6-71 Non-Turbo – 4-Valve Head

The 6-71 4-valve non-turbo engine is valued across industries for its enhanced airflow, fuel efficiency, and manageable power band, all while maintaining the simplicity of a non-turbocharged platform. The extra valve area in each cylinder enables more complete combustion, better exhaust evacuation, and a cleaner-running engine overall.

Marine Applications

In the marine sector, the 6-71 4-valve naturally aspirated engine is commonly found in vessels that prioritize reliability, mechanical simplicity, and moderate horsepower.

Typical Marine Use Cases

Coastal fishing vessels and longliners
Charter fishing and dive boats
Inshore shrimpers
Small pilot and harbor patrol boats
River ferries and water taxis
Older trawlers and converted working boats

With a typical output of 210–230 HP, this engine is often paired with Twin Disc or Allison marine transmissions, allowing it to operate efficiently in single or twin-engine configurations. It’s particularly suited for harbor maneuvering and long idle periods followed by periods of steady cruising.

Industrial and Stationary Applications

Due to its fuel economy and consistent torque curve, the 6-71 non-turbo 4-valve engine is well-suited for industrial power generation and mechanical drive systems.

Common Industrial Uses

Generator sets (prime and standby configurations)
Water and slurry pumping stations
High-capacity fire pump systems for refineries
Material conveyor systems
Crushers and screening plants in quarry operations
Oilfield support rigs and winch systems

This engine continues to see use in remote operations where electronics are not welcome, and mechanical reliability is non-negotiable. Its 4-valve design provides just enough edge in airflow and efficiency to outperform the older 2-valve setup under variable industrial loads.

Ground-Based Vehicles and Utility Equipment

The 6-71N 4-valve was a factory option in a number of commercial transportation and municipal service platforms. It offered additional torque and fuel economy for fleets that operated in city environments or required more robust load-hauling capabilities.

Common Vehicle Applications

Transit and intercity buses (GM PD4106, PD4903, etc.)
Fire engines (especially with front-mount pumps)
Dump trucks and refuse haulers
Cement mixers
Army transport and engineering vehicles
Airport tugs and ground support equipment

Many of these units are still in use in South America, Southeast Asia, and other regions where repowered buses and military surplus trucks are popular.

Restoration, Repowers, and Custom Installs

Given its durability and nostalgic status, the 6-71 4-valve naturally aspirated version is frequently used in restoration projects and specialty repowers.

Popular Restoration Uses

Classic working boat restorations
Vintage GM, Flxible, or MCI buses
Custom overland expedition trucks
Industrial museum and display engines
Repowered oilfield service trucks
Engine swaps into military surplus vehicles

Builders prefer the 4-valve head when they want to preserve the classic 6-71 sound and feel while gaining improved performance without stepping into the complexity of turbocharged configurations.

Summary Table – Detroit Diesel 6-71 Non-Turbo, 4-Valve Head

Feature	Specification
Engine Type	Inline 6-cylinder, 2-stroke diesel
Valve Configuration	4 valves per cylinder
Displacement	426 cubic inches (6.99 liters)
Aspiration	Roots blower (no turbocharger)
Horsepower Range	210–238 HP @ 2,100 RPM
Peak Torque	475–525 lb-ft @ 1,200–1,600 RPM
Fuel System	Mechanical unit injectors
Oil Capacity	5.5–6 gallons (20.8–22.7 liters)
Coolant Capacity	4–5 gallons (15–19 liters)
Operating Temperature	170°F–190°F
Typical Applications	Fishing vessels, fire pumps, gensets, buses, winches