Subaru EN07 Specifications
| Engine Model: Subaru EN07 |
| Engine Type: 4-cycle inline 4-cylinder liquid-cooled gasoline |
| Total Displacement: 40.1 cu.in (0.65 L) |
| Rated Engine Power: 45-63 Hp (34-47 kW) at 6000 rpm |
| Fuel System Type: Electronic fuel injection |
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The Subaru EN07 is a 658 cc liquid-cooled inline-four
gasoline engine developed to comply with Japanese Kei car regulations.
Introduced in 1989, it succeeded the two-cylinder EK series, providing a
substantial improvement in refinement, power output, and operational smoothness.
The EN07 remained in production for over two decades, becoming the cornerstone
powerplant for Subaru’s Kei-class passenger cars, vans, and light commercial
vehicles.
The EN07 is distinguished by its inline-four configuration in a displacement
class where competitors predominantly utilized three-cylinder engines. This
design choice delivered superior smoothness and a more refined power delivery,
characteristics that were particularly valued in the Kei car segment. The
engine’s all-aluminum construction comprised a cast aluminum block with cast
iron cylinder liners and an aluminum cylinder head.
A wide array of induction and valvetrain variants were developed throughout its
production run. The naturally aspirated SOHC 8-valve versions prioritized fuel
economy and low-end tractability, while the introduction of a supercharger
provided forced induction without the lag associated with turbochargers - a
deliberate engineering choice to enhance throttle response in urban driving
conditions. The highest-performance variant, the EN07X, combined a DOHC 16-valve
cylinder head with an intercooled supercharger to produce 64 PS, the maximum
permitted under Kei car regulations.
Later naturally aspirated variants, such as the EN07D, incorporated AVCS (Active
Valve Control System) variable valve timing to improve efficiency and broaden
the torque curve. The engine’s durability is well-documented, particularly in
the rear-engine Subaru Sambar, where it frequently exceeds 200,000 km with
consistent maintenance, though its small coolant and oil capacities demand
diligent attention to fluid levels and cooling system integrity.
Engine Type: Inline-4, naturally aspirated or supercharged.
Displacement: 658 cc (40.1 cu.in).
Bore: 56.0 mm (2.20 in).
Stroke: 66.8 mm (2.63 in).
Compression Ratio: 10.0:1 (EN07E SOHC NA).
Compression Ratio: 8.5:1-9.0:1 (supercharged variants).
Engine Management System: EMPi or later MPI systems.
Ignition System: Electronic, distributor-based or distributorless.
Firing Order: 1-3-4-2.
Max Power (SOHC NA): 34-40 kW (45-53 hp) @ 6,400 rpm.
Max Power (EN07Z SOHC SC): 47 kW (63 hp) @ 6,000 rpm.
Max Power (EN07X DOHC SC): 47 kW (63 hp) @ 6,000 rpm.
Max Torque (SOHC NA): 54 Nm (40 lb-ft) @ 4,400 rpm.
Max Torque (EN07Z SOHC SC): 84-103 Nm (62-76 lb-ft) @ 4,000 rpm.
Max Torque (EN07X DOHC SC): 103 Nm (76 lb-ft) @ 4,000 rpm.
Redline: 7,000 rpm (naturally aspirated); 6,500 rpm (supercharged).
The cylinder block is constructed from aluminum alloy
with cast iron wet-type cylinder liners. This all-aluminum construction reduces
overall engine mass, a critical consideration for Kei car applications where
weight directly affects performance and fuel economy. The block is of an
open-deck design, with the cylinder liners supported by the surrounding aluminum
structure. The crankcase is integrated into the block casting, featuring five
main bearing caps.
The inline-four configuration provides inherent primary and secondary balance,
contributing to the engine’s smooth operation compared to three-cylinder
competitors. The block incorporates oil galleries for the valvetrain and
crankshaft bearings. Coolant passages are arranged to provide uniform cooling
around each cylinder liner, with a water pump housing cast into the front of the
block on front-engine applications. For rear-engine Sambar applications, the
block was modified with a different water pump and accessory drive arrangement
to suit the longitudinal rear-mount orientation.
The cylinder head is a single-piece casting in aluminum
alloy, with design variations corresponding to the different valvetrain
configurations. Early naturally aspirated variants utilized an SOHC design with
two valves per cylinder, actuated via rocker arms. Later SOHC supercharged
variants retained the two-valve-per-cylinder layout but incorporated reinforced
valve springs to accommodate forced induction.
The high-performance EN07X employed a DOHC design with four valves per cylinder,
actuated by bucket tappets with shim adjustment. The late-model EN07D naturally
aspirated variant combined a DOHC 16-valve layout with AVCS variable valve
timing on the intake camshaft.
Valves (SOHC): 8 total (4 intake, 4 exhaust)
Valves (DOHC): 16 total (8 intake, 8 exhaust)
Intake Valve Diameter (SOHC): 28.0 mm (1.10 in)
Exhaust Valve Diameter (SOHC): 24.5 mm (0.96 in)
Intake Valve Diameter (DOHC): 29.0 mm (1.14 in)
Exhaust Valve Diameter (DOHC): 25.0 mm (0.98 in)
Valve Stem Diameter: 5.5 mm (0.22 in) for all variants
Valve Seat Material: Sintered alloy steel inserts
The combustion chamber design varies by variant: the SOHC heads utilize a
wedge-type chamber, while DOHC heads employ a pent-roof configuration for
improved volumetric efficiency. The intake ports are designed to generate swirl
for better fuel atomization, particularly important in the small-displacement
format.
The EN07 utilizes Subaru’s EMPi (Electronic Multi-Point
Injection) system across most variants, evolving to more advanced MPI systems in
later production years. The system employs multi-point port injection, with one
fuel injector per cylinder mounted in the intake manifold runners. A returnless
fuel system is used on later variants, with a fuel pressure regulator integrated
into the fuel pump assembly within the fuel tank.
The fuel system operates at a nominal pressure of 3.0 bar (43.5 psi). The ECU
controls injection timing and duration based on inputs from the mass air flow
sensor, throttle position sensor, engine coolant temperature sensor, and oxygen
sensor. On supercharged variants, the fuel map is calibrated to provide
enrichment under boost conditions to maintain the optimal air-fuel ratio. The
EMPi system is noted for its reliability and simplicity, contributing to the
engine’s overall durability.
The lubrication system is a pressurized, wet-sump
design with a rotor-type oil pump driven directly by the crankshaft. The pump is
mounted within the front cover assembly and draws oil from a stamped steel or
aluminum oil pan through a screened pickup tube. A full-flow, spin-on oil filter
is mounted externally on the engine block.
The system supplies oil to the five main bearings, connecting rod bearings,
camshaft bearings, and, on DOHC variants, the hydraulic or mechanical lash
adjusters. Supercharged variants incorporate an additional oil feed line to the
supercharger unit for lubrication of the internal rotors and bearings.
Oil Capacity (including filter): 3.2 liters (3.4 US qt) for front-engine
applications; 3.5 liters (3.7 US qt) for rear-engine Sambar. Oil Pressure at
3,000 rpm: 300-450 kPa (43.5-65.3 psi). Recommended Oil Viscosity: 5W-30 or
10W-30, API SG/SH or higher. Oil Pump Type: Rotor-type, crankshaft-driven.
The cooling system is a pressurized, thermosiphon
design with a belt-driven water pump. The water pump is mounted to the front of
the cylinder block on front-engine applications and to the side of the block on
rear-engine Sambar configurations to accommodate the different vehicle layout.
Coolant flows from the radiator through the pump, into the cylinder block
passages surrounding the cylinders, then upward through the cylinder head, and
returns to the radiator through the thermostat housing.
A wax-type thermostat maintains an operating temperature between 82-88 °C
(180-190 °F). The system utilizes a cross-flow radiator with an electric cooling
fan controlled by a thermostatic switch or the ECU. The cooling system is
critical for engine longevity, as the EN07’s small coolant capacity - 3.5 liters
(3.7 US qt) in most applications - provides limited thermal buffering.
Intake System: The intake manifold is constructed from
aluminum or plastic, with runner lengths tuned to optimize torque in the
low-to-mid rpm range. Supercharged variants incorporate a roots-type
supercharger mounted above the intake manifold, driven by a belt from the
crankshaft. Intercooled variants, such as the EN07X, include an air-to-air
intercooler mounted forward of the radiator.
Supercharging System: Subaru selected a roots-type supercharger for forced
induction applications to provide instant throttle response and linear power
delivery. The supercharger is equipped with an electromagnetic clutch that
disengages under light load to reduce parasitic drag and improve fuel economy. A
bypass valve recirculates air during deceleration to prevent compressor surge.
Exhaust System: A stainless steel exhaust manifold routes gases to a single
three-way catalytic converter. An oxygen sensor upstream of the catalyst
provides closed-loop feedback to the fuel injection system.
Ignition System: Early EN07 variants employed a distributor-based electronic
ignition system with vacuum and centrifugal advance. Later variants,
particularly those with DOHC valvetrains, utilized a distributorless
coil-on-plug system with individual ignition coils mounted directly over each
spark plug. Ignition timing is fully controlled by the ECU.
Emissions Control: The engine incorporates a three-way catalytic converter,
closed-loop air-fuel ratio control, a positive crankcase ventilation (PCV)
system, and an evaporative emissions (EVAP) system with a charcoal canister and
purge solenoid to meet Japanese Kei car emissions standards.
Overall Length: 520 mm (20.5 in)
Overall Width: 590 mm (23.2 in)
Overall Height: 610 mm (24.0 in)
Dry Weight (complete engine): 65 kg (143 lb) for naturally aspirated SOHC
Dry Weight (complete engine): 75 kg (165 lb) for supercharged DOHC
Valve Clearance (SOHC, mechanical rockers): Intake
0.20-0.24 mm (0.008-0.009 in); Exhaust 0.23-0.27 mm (0.009-0.011 in) when engine
is cold. Adjustment by screw and locknut. Valve Clearance (DOHC, mechanical
bucket): Intake 0.18-0.22 mm (0.007-0.009 in); Exhaust 0.23-0.27 mm (0.009-0.011
in). Adjustment by shim replacement. Valve Clearance (AVCS variants): Hydraulic
lash adjusters - no manual adjustment required.
Timing Belt Replacement Interval: 100,000 km (62,000 mi) for all variants.
Engine Oil Change Interval: 5,000 km (3,100 mi) or 6 months. Oil Filter
Replacement: With every oil change. Spark Plug Type: NGK BKR5E-11 or equivalent.
Spark Plug Gap: 1.0-1.1 mm (0.039-0.043 in). Spark Plug Replacement Interval:
20,000 km (12,400 mi) for copper core; 100,000 km (62,000 mi) for iridium.
Coolant Replacement Interval: 40,000 km (25,000 mi) or 2 years. Accessory Drive
Belt Inspection: Every 10,000 km (6,200 mi); replacement interval of 40,000 km
(25,000 mi). Supercharger Drive Belt Inspection: Every 20,000 km (12,400 mi);
replacement with oil filter service.
Cylinder Head Bolts (Step 1): 30 Nm (22 lb-ft)
Cylinder Head Bolts (Step 2): 60 Nm (44 lb-ft)
Connecting Rod Cap Bolts: 35 Nm (26 lb-ft)
Main Bearing Cap Bolts: 50 Nm (37 lb-ft)
Camshaft Bearing Cap Bolts (SOHC): 15 Nm (11 lb-ft)
Camshaft Bearing Cap Bolts (DOHC): 22 Nm (16 lb-ft)
Intake Manifold Bolts: 18 Nm (13 lb-ft)
Exhaust Manifold Nuts: 25 Nm (18 lb-ft)
Spark Plugs: 18 Nm (13 lb-ft)
Oil Filter: 12 Nm (9 lb-ft)
Oil Drain Plug: 40 Nm (30 lb-ft)
Crankshaft Pulley Bolt: 120 Nm (89 lb-ft)
Flywheel/Flexplate Bolts: 55 Nm (41 lb-ft)
The Subaru EN07 engine powered the majority of Subaru’s
Kei-class vehicles from 1989 through the early 2010s, with applications spanning
passenger cars, vans, and light commercial trucks.
Subaru Vivio (KV3, KV4): Produced from 1992 to 1998, the Vivio utilized the EN07
across its range. The EN07E powered base models, while the EN07Z supercharged
variant was featured in the Vivio Bistro and GX. The EN07X DOHC supercharged
engine was reserved for the Vivio RX-R and related performance-oriented models.
Subaru Pleo (RA1, RA2): Introduced in 1998 as the successor to the Vivio, the
Pleo employed the EN07E naturally aspirated SOHC engine in base trims and the
EN07Z supercharged SOHC in higher-grade variants. Production continued through
2010.
Subaru Stella (L110, L210): Produced from 2006 to 2011, the Stella utilized the
EN07E and later the EN07D DOHC naturally aspirated engine with AVCS variable
valve timing. The Stella represented the final passenger car application of the
EN07.
Subaru R1 (RJ) and R2 (RC): Produced from 2003 to 2010, the R1 and R2 Kei cars
utilized EN07 variants. The R2 employed the EN07E in base models and the EN07Z
supercharged engine in the R2 S and Custom trims.
Subaru Sambar (TV1, TV2, TT1, TT2): The Sambar microvan and pickup truck
utilized the EN07 from 1990 through 2012. In this application, the engine was
mounted longitudinally at the rear of the vehicle, driving the rear wheels. The
Sambar utilized naturally aspirated EN07E and EN07C variants, with supercharged
versions offered in higher-trim passenger vans.
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