Mitsubishi 6B31 Specifications
| Engine Model: Mitsubishi 6B31 |
| Engine Type: 4-cycle 6-cylinder V-block SOHC 24-valve liquid-cooled gasoline |
| Total Displacement: 182.9 cu.in (2.99 L) |
| Rated Engine Power: 220-230 Hp (162-169 kW) at 6250 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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The Mitsubishi 6B31 is a 3.0-liter, 60-degree V6
gasoline engine that debuted in 2006 as part of Mitsubishi’s new-generation
B-series engine family. Designed to replace the aging 6G72 V6, the 6B31 was
engineered to deliver improved power, reduced weight, and enhanced fuel
efficiency through the application of all-alloy construction and advanced
valvetrain technology. The engine was developed primarily for Mitsubishi’s
mid-size sport utility vehicles and crossovers, where its combination of low-end
torque and high-rpm power proved well-suited to both on-road refinement and
off-road capability.
The 6B31 features an aluminum cylinder block and cylinder heads, a belt-driven
single overhead camshaft (SOHC) valvetrain, and Mitsubishi’s MIVEC (Mitsubishi
Innovative Valve timing and lift Electronic Control) system, which provides
variable valve timing and variable valve lift on the intake side. The engine
incorporates a two-stage variable intake manifold and electronic throttle
control to further optimize torque delivery across the engine speed range. Over
its production life, the 6B31 received a significant update around 2010 that
increased the compression ratio from 9.5:1 to 10.5:1, resulting in higher power
and torque outputs while maintaining compatibility with regular-grade fuel.
The 6B31 is a naturally aspirated, water-cooled, four-stroke V6 engine
configured for longitudinal mounting in rear-wheel-drive and four-wheel-drive
vehicle architectures, as well as transverse mounting in certain applications.
Its 60-degree bank angle provides inherent primary and secondary balance,
contributing to smooth operation.
Engine Type: 60° V6, 4-cycle, water-cooled, naturally aspirated.
Displacement: 2,998 cc (182.9 cu.in).
Bore and Stroke: 87.6 mm (3.45 in) x 82.9 mm (3.26 in).
Valvetrain: SOHC, 24-valve (4 valves per cylinder) with MIVEC on intake.
Firing Order: 1-2-3-4-5-6.
Redline: 6,500 rpm.
Pre-2010 Variants
Compression Ratio: 9.5:1.
Maximum Power: 162 kW (220 Hp) at 6,250 rpm.
Maximum Torque: 276 Nm (204 lb-ft) at 4,000 rpm.
2010 and Later Variants
Compression Ratio: 10.5:1.
Maximum Power: 169 kW (230 Hp) at 6,250 rpm.
Maximum Torque: 291 Nm (215 lb-ft) at 3,750-4,000 rpm.
The cylinder block is manufactured from aluminum alloy
using a high-pressure die-casting process, a material selection that
significantly reduces overall engine mass compared to the cast iron blocks of
earlier V6 engines. The block features a 60-degree V-angle and an open-deck
design, where the cylinder bores are supported at the top only by the water
jacket perimeter, enhancing cooling efficiency around the upper cylinder area
while minimizing casting complexity. Cast-in-place, iron-coated aluminum
cylinder bores are machined directly into the block casting, with a
high-phosphorus content applied to the bore surface to provide a durable,
low-friction running surface.
The block incorporates a deep-skirt design extending below the crankshaft
centerline, with a structural aluminum ladder frame - a bedplate - bolted to the
lower crankcase to support the crankshaft main bearings and enhance bottom-end
rigidity. The bedplate design incorporates four-bolt main bearing caps
integrated into the structure. The block is configured to accommodate both
longitudinal and transverse mounting orientations depending on the vehicle
platform.
Block Material: Aluminum alloy.
Bore Diameter: 87.6 mm (3.45 in).
Main Bearing Configuration: Four-bolt caps integrated into bedplate.
Balance Shafts: Not equipped (V6 configuration provides inherent balance).
The cylinder heads are constructed from aluminum alloy,
with separate castings for each cylinder bank. The SOHC valvetrain operates
twenty-four valves - four per cylinder - via roller rocker arms. The defining
feature of the 6B31 is the MIVEC system, which operates on the intake valves.
This system uses two distinct cam profiles per intake valve: a low-lift,
short-duration profile for low-rpm operation that enhances fuel economy and idle
stability, and a high-lift, long-duration profile that engages at approximately
4,750 rpm to increase airflow and power output at high engine speeds. The system
also provides variable valve timing on the intake camshaft.
The exhaust camshaft operates without variable lift but incorporates fixed
timing optimized for exhaust scavenging. The camshafts are driven by a
reinforced rubber timing belt from the crankshaft, with an automatic
spring-loaded tensioner maintaining belt tension. The engine is of interference
design; timing belt failure results in valve-to-piston contact. Hydraulic lash
adjusters are not used; valve clearance is set by selecting mechanical tappets
of varying thicknesses.
Head Material: Aluminum alloy.
Valve Configuration: SOHC, 4 valves per cylinder with roller rocker
arms.
MIVEC Engagement: Intake cam profile switching at 4,750 rpm.
Valve Diameter (Intake): 33.0 mm (1.30 in).
Valve Diameter (Exhaust): 27.5 mm (1.08 in).
Valve Stem Diameter: 5.5 mm (0.22 in).
Valve Seat Angle: 45 degrees.
Valve Clearance (Cold, Intake): 0.17-0.23 mm (0.0067-0.0091 in).
Valve Clearance (Cold, Exhaust): 0.27-0.33 mm (0.0106-0.0130 in).
The 6B31 employs a multi-point electronic fuel
injection (MPI) system with sequential injection. Six fuel injectors - three per
cylinder bank - are mounted in the intake manifold, positioned to spray fuel
directly onto the back of the intake valves. This port injection design provides
excellent air-fuel mixture preparation, immediate throttle response, and
maintains intake valve cleanliness, eliminating the carbon buildup concerns
associated with direct injection systems.
The intake manifold incorporates a two-stage variable induction system. A set of
butterfly valves within the intake plenum switches at approximately 3,600 rpm
between long intake runners for enhanced low-end torque and short intake runners
for improved high-rpm power. The system is controlled by the engine control unit
(ECU) based on engine speed and throttle position. An electronic throttle body -
drive-by-wire - eliminates the mechanical cable connection, allowing the ECU to
manage throttle opening for precise torque control and idle stability.
Injection Type: Multi-point sequential electronic fuel injection.
Intake System: Two-stage variable intake manifold.
Variable Intake Activation Point: 3,600 rpm.
Fuel Pressure: 324-392 kPa (47.0-56.9 psi).
Fuel Injector Resistance: 12.0-16.0 Ohms.
Fuel Requirement: 87 octane or higher (Research Octane Number 91 or higher).
0The lubrication system is a fully pressurized,
wet-sump design utilizing a gear-type oil pump mounted to the front of the
crankshaft. The oil pump draws lubricant from a cast aluminum oil pan through a
mesh strainer and circulates it through a full-flow, replaceable oil filter
before entering the main oil gallery. From the gallery, pressurized oil is
distributed to the crankshaft main bearings, connecting rod bearings, camshaft
bearings, roller rocker arms, and MIVEC actuators.
A pressure relief valve integrated into the oil pump maintains system pressure
within operational limits. The oil pan incorporates internal baffles to maintain
oil pickup during cornering and acceleration. An oil cooler is integrated into
the oil filter housing on certain applications to stabilize oil temperature
under sustained high-load operation.
Oil Type: SAE 0W-20, 5W-20, or 5W-30 (API SM or higher; ILSAC GF-4 or higher).
Oil Capacity (with filter): 4.3-4.6 liters (4.5-4.9 US qt) depending on
application.
Oil Pressure (at idle): 98 kPa (14.2 psi) minimum.
Oil Pressure (at 3,000 rpm): 294-392 kPa (42.6-56.9 psi).
Oil Pump Type: Gear-type, crankshaft-driven.
The cooling system is a pressurized, liquid-cooled
design engineered to manage the thermal load of a high-compression V6 engine. A
cross-flow aluminum radiator with an electric cooling fan provides cooling
capacity for sustained operation. A centrifugal-type water pump, driven by the
timing belt, circulates coolant through the cylinder block, cylinder heads, and
heater core.
A wax-pellet thermostat regulates coolant flow to maintain optimal operating
temperature, with a bypass circuit that allows the engine to warm rapidly. The
system is designed to provide uniform cooling across both cylinder banks,
maintaining consistent thermal expansion across the aluminum block and head
interface.
Coolant Type: Ethylene-glycol based antifreeze with corrosion inhibitors.
Coolant Capacity: 7.0-8.0 liters (7.4-8.5 US qt) depending on radiator
configuration.
Thermostat Opening Temperature: 82-86 °C (180-187 °F).
Thermostat Full-Open Temperature: 95 °C (203 °F).
Radiator Cap Pressure: 108-127 kPa (15.7-18.4 psi).
Water Pump Type: Centrifugal, timing belt-driven.
Ignition System: Distributorless ignition system with
six individual pencil-type ignition coils, each mounted directly over a spark
plug (coil-on-plug). The ECU controls ignition timing based on crankshaft
position, camshaft position, knock sensor feedback, and engine load. A knock
sensor mounted on the cylinder block allows the ECU to retard ignition timing
under detonation conditions.
Intake System: Air is drawn through a dry-type paper element air filter and a
mass airflow sensor before entering the electronic throttle body. The two-stage
variable intake manifold distributes air to both cylinder banks.
Exhaust System: Stainless steel exhaust manifolds from each cylinder bank merge
into a Y-pipe configuration before entering a catalytic converter. Heated oxygen
sensors are mounted upstream and downstream of the catalytic converter for fuel
trim feedback and catalyst efficiency monitoring.
Timing Drive: A reinforced rubber timing belt with integral teeth drives the
camshafts from the crankshaft sprocket. The belt routes around idler pulleys and
is tensioned by an automatic spring-loaded hydraulic tensioner. The engine is of
interference design; timing belt failure results in valve-to-piston contact.
Overall Length: 620 mm (24.4 in)
Overall Width: 730 mm (28.7 in)
Overall Height: 680 mm (26.8 in)
Dry Weight (complete engine): 145 kg (320 lb)
Oil Change Interval: 10,000 km (6,000 mi) under normal
driving conditions; 5,000 km (3,000 mi) under severe conditions. Oil Filter
Change: At every oil change. Timing Belt Replacement: 160,000 km (100,000 mi) or
8 years. Engine Coolant Replacement: 120,000 km (75,000 mi) or 5 years.
Spark Plug Replacement: 100,000 km (60,000 mi) for iridium plugs. Spark Plug
Type: NGK ILKR7B-8 or Denso SXU22HDR8. Spark Plug Gap: 0.7-0.8 mm (0.028-0.031
in). Drive Belt (Accessory) Inspection: Every 15,000 km (9,000 mi) for tension,
cracking, and glazing.
Air Filter Replacement: 30,000 km (18,000 mi) or as indicated by inspection.
Fuel Filter: Integrated with fuel pump assembly; no scheduled replacement. Valve
Clearance Adjustment: Inspect and adjust as required. Intake: 0.17-0.23 mm
(0.0067-0.0091 in) cold. Exhaust: 0.27-0.33 mm (0.0106-0.0130 in) cold.
Clearance is set by replacing mechanical tappets.
Cylinder Head Bolts (M10 x 1.25), 1st pass: 30 Nm (22
lb-ft).
Cylinder Head Bolts (M10 x 1.25), 2nd pass: 60 Nm (44 lb-ft).
Main Bearing Bedplate Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Connecting Rod Cap Bolts (M8 x 1.0): 15 Nm (11 lb-ft).
Camshaft Bearing Cap Bolts (M6 x 1.0): 10-12 Nm (89-106 lb-in).
Intake Manifold Bolts (M6 x 1.0): 10-12 Nm (89-106 lb-in).
Exhaust Manifold Nuts (M8 x 1.25): 20-25 Nm (15-18 lb-ft).
Spark Plugs: 20-25 Nm (15-18 lb-ft).
Oil Pan Bolts (M6 x 1.0): 10-12 Nm (89-106 lb-in).
Water Pump Bolts (M6 x 1.0): 10-12 Nm (89-106 lb-in).
Timing Belt Tensioner Bolt (M10 x 1.25): 35-40 Nm (26-30 lb-ft).
Crankshaft Pulley Bolt (M14 x 1.5): 180-200 Nm (133-148 lb-ft).
Flywheel / Drive Plate Bolts (M10 x 1.25): 45 Nm (33 lb-ft).
The Mitsubishi 6B31 engine was utilized across a range
of Mitsubishi sport utility vehicles, crossovers, and pickup-based platforms,
serving as the premium gasoline powerplant in markets where diesel options were
less prevalent.
Mitsubishi Outlander (CW, ZJ, ZK, ZL generations): 2006-present (3.0-liter V6
variants).
Mitsubishi Pajero Sport / Montero Sport / Challenger (KG, KH, KK, KL
generations): 2008-present (3.0-liter V6 variants).
Mitsubishi Delica D:5 (CV series): 2007-present (3.0-liter V6 variants in select
markets).
Mitsubishi Lancer (aftermarket): The 6B31 has been utilized in performance
conversions and aftermarket installations, though not factory-equipped in Lancer
models.
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