Honda B20A5 Specifications
| Engine Model: Honda B20A5 |
| Engine Type: 4-cycle inline 4-cylinder DOHC 16-valve liquid-cooled gasoline |
| Total Displacement: 119.5 cu.in (1.96 L) |
| Rated Engine Power: 135 Hp (101 kW) at 6000 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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The Honda B20A5 engine represents one of the
most distinctive and historically significant powerplants in the lineage
of Honda’s early B-series engines. Before the widespread adoption of
VTEC technology, Honda relied on precise mechanical engineering,
optimized combustion chamber design, carefully crafted port geometry,
and robust bottom-end construction to deliver strong performance and
exceptional reliability in naturally aspirated configurations.
The B20A5, used primarily in North American
third-generation Honda Prelude models from the late 1980s to early
1990s, served as the higher-output version of the B20A engine family. It
is characterized by its long-stroke configuration, efficient DOHC
valvetrain, crossflow aluminum head, and forward-leaning block
architecture unique to the early B20 family.
While it predates the later and more widely recognized B16A, B18A/B, and
VTEC-equipped B18C engines, the B20A5 was instrumental in demonstrating
Honda’s commitment to performance-oriented engineering long before
advanced variable valve timing was available. The engine provided
excellent midrange torque, smooth throttle response, and durable
long-term operation.
It offered a blend of everyday drivability and
sporty performance that appealed to drivers seeking more dynamic
behavior from their 2.0-liter Prelude models. Today, the B20A5 is
appreciated by enthusiasts who respect its mechanical simplicity,
reliability, and its place in Honda’s evolution toward the later
B-series performance engines.
The Honda B20A5 is a four-stroke, inline-four internal combustion engine
with a total displacement of 1,958 cc (119.5 cubic inches). Bore is 81.0
mm (3.19 inches), while stroke measures 95.0 mm (3.74 inches). This
notable long-stroke geometry gives the B20A5 strong torque
characteristics and excellent mid-range pulling power. The compression
ratio is approximately 9.3:1, marginally higher than some earlier B20A
variants, allowing improved thermal efficiency without increasing
sensitivity to low-octane fuel.
Factory power output for the B20A5 is rated at approximately 135
horsepower (101 kW) at around 6,000 rpm. Peak torque is roughly 127
lb-ft (172 Nm) at approximately 4,800 rpm. The engine idles at
approximately 750 ± 50 rpm, and the recommended redline is near 6,500
rpm. Despite this relatively conservative redline compared to later
high-revving Honda B-series units, the B20A5 is capable of sustained
operation at elevated rpm thanks to its robust rotating assembly and
efficient head design. The firing order is 1-3-4-2, consistent with most
Honda inline-four engines.
The block is cast iron with an integrated forward lean angle of around
18–20 degrees. This unusual block geometry, specific to early B20
designs, was chosen to optimize hood line height and engine bay
packaging for the Prelude chassis. The cylinders feature cast-in liners
for long-term durability. A forged-steel crankshaft supported by five
main bearings ensures excellent rotational stability.
Forged-steel connecting rods are paired with
full-floating wrist pins, and the pistons are cast aluminum alloy with
skirt coatings to reduce friction. The piston ring set uses two
compression rings and one oil-control ring for stable sealing across the
engine’s broad temperature range.
The aluminum DOHC cylinder head features a 16-valve crossflow
configuration, with two intake and two exhaust valves per cylinder. The
intake valves measure around 33 mm (1.30 inches) in diameter, while
exhaust valves measure approximately 28 mm (1.10 inches). Valve
actuation is provided through shim-over-bucket mechanical lifters,
ensuring stable timing at high engine speeds. The combustion chambers
follow a pent-roof design optimized for efficient mixture swirl, flame
propagation, and detonation resistance.
Camshaft profiles in the B20A5 are more aggressive compared to earlier
B20A engines, improving airflow at higher rpm and contributing to the
engine’s increased power rating. Cam drive is achieved through a
reinforced rubber timing belt that also drives the water pump. The
timing belt should be replaced at regular intervals to maintain
reliability.
Intake and exhaust port geometry emphasizes midrange torque and
efficient breathing. The intake manifold is engineered to maintain high
airflow velocity, while the cast-iron exhaust manifold balances
durability with adequate flow characteristics for a naturally aspirated
2.0-liter engine.
The B20A5 uses Honda’s PGM-FI multi-point electronic fuel injection
system. Fuel is supplied by an electric in-tank pump and delivered
through a fine-element filter to a rigid fuel rail. Each of the engine’s
four intake ports is supplied by an electronically controlled solenoid
injector.
Fuel pressure is regulated to approximately 40–47 psi (275–325 kPa)
using a vacuum-referenced fuel-pressure regulator. Excess fuel flows
back to the tank, ensuring constant rail pressure regardless of engine
load. The fuel injectors are sized appropriately for the B20A5’s output
and respond quickly to ECU pulse-width modulation.
Essential sensors used by the PGM-FI system
include:
– Manifold Absolute Pressure (MAP) sensor
– Throttle Position Sensor (TPS)
– Intake Air Temperature (IAT) sensor
– Engine Coolant Temperature (ECT) sensor
– Oxygen sensor for closed-loop operation
– Atmospheric pressure sensor
– Internal crankshaft and camshaft position sensors located within the
distributor
The ECU dynamically adjusts injector pulse width based on rpm, load,
coolant temperature, and oxygen sensor feedback. Recommended fuel is
unleaded gasoline with at least 87 AKI (91 RON), though higher octane
may improve knock resistance in high-load conditions.
The B20A5 uses a full-pressure wet-sump lubrication system. A
crankshaft-driven trochoid oil pump draws oil from the sump, passes it
through a steel-mesh pickup, pressurizes it, and distributes it through
a full-flow spin-on oil filter. The oil system lubricates the crankshaft
bearings, connecting rod journals, camshaft journals, and valve train
components.
Oil capacity is approximately 4.0 liters (4.2 US quarts). Recommended
viscosity is SAE 5W-30 or 10W-30 depending on climate, though 10W-40 may
be used in hotter regions. Oil pressure typically measures 50–70 psi
(345–480 kPa) at operating speed, with idle pressure above 10 psi (69
kPa). A PCV valve regulates crankcase pressure and reduces blow-by
contamination.
Engine cooling is handled by a liquid-based, forced-circulation system.
A belt-driven centrifugal water pump circulates coolant through the
engine block, aluminum head, heater core, and radiator. The thermostat
begins opening at around 82°C (180°F) and is fully open at roughly 95°C
(203°F).
Coolant capacity is approximately 5.5–6.0 liters (5.8–6.3 US quarts).
The coolant mixture should consist of 50% ethylene glycol antifreeze and
50% distilled water. A radiator cap rated at approximately 1.1 bar (16
psi) maintains system pressure. The electric radiator fan is activated
by a thermal switch, while the ECU uses coolant-temperature data for
fuel and ignition adjustments.
| Intake and Exhaust Systems |
The intake manifold is an aluminum casting engineered for strong
midrange torque. Its runners are shaped to maintain high air velocity,
improving throttle response. The throttle body generally measures around
58–60 mm in diameter. Air is directed through a resonated airbox
containing a replaceable dry-element filter.
The exhaust manifold is cast iron and designed for durability. Exhaust
gases pass through the oxygen sensor, catalytic converter, resonator,
and muffler. While the manifold sacrifices some top-end flow for
durability, it provides stable operation for long-term use.
| Ignition and Electrical System |
Ignition is provided by a distributor-based electronic ignition system.
The distributor houses the internal ignition coil, igniter module, and
pickup sensors for crank and cam position. The ECU calculates optimal
spark timing using load, temperature, and rpm data, then commands the
igniter to trigger the coil at precisely the correct moment.
Standard spark plugs are NGK ZFR6F-11 or equivalent, with a recommended
gap of 1.0–1.1 mm (0.039–0.043 inches). High-tension spark plug wires
ensure reliable spark delivery. Base timing adjustment is accomplished
by rotating the distributor slightly while the ECU is locked into
base-timing mode through the service connector.
The engine uses a 12-volt electrical system. The alternator typically
produces between 70 and 80 amperes. The starter motor is a
reduction-gear design that ensures reliable cold-start performance.
Proper grounding is essential for ECU accuracy and sensor stability.
| VALVE TIMING AND DRIVE MECHANISM |
Camshafts are driven by a toothed rubber timing belt. Honda recommends
replacing the belt every 90,000–100,000 km (55,000–62,000 miles). A
spring-loaded tensioner maintains consistent belt tension. The timing
belt also drives the water pump. Valve clearance is set manually using
shim-over-bucket lifters and must be inspected periodically to ensure
optimal efficiency and quiet operation.
Length: 640 mm (25.2 inches)
Width: 580 mm (22.8 inches)
Height: 670 mm (26.4 inches)
Dry weight falls between 145 and 155 kg (320–342 lbs), depending on
accessory configuration.
Recommended maintenance intervals include:
Oil and filter: every 5,000–7,500 km (3,000–4,600 miles)
Air filter: every 20,000–30,000 km
Fuel filter: every 40,000–50,000 km
Spark plugs: every 20,000–30,000 km
Valve clearance: every 40,000–50,000 km
Coolant: every 40,000 km or every 2 years
Timing belt: every 90,000–100,000 km
PCV valve: inspect at major service intervals
A healthy B20A5 typically produces between 170 and 200 psi (1,170–1,380
kPa) of compression, with no more than 10% variation among cylinders.
Cylinder head bolts: 29 Nm (21 lb-ft) - 59 Nm (44 lb-ft) - +90° - +90°
Main bearing caps: 65–70 Nm (48–52 lb-ft)
Connecting rod bolts: 40–45 Nm (30–33 lb-ft)
Camshaft cap bolts: 10 Nm (7 lb-ft)
Crankshaft pulley bolt: 180–190 Nm (133–140 lb-ft)
Flywheel bolts: 85–95 Nm (63–70 lb-ft)
Spark plugs: 18 Nm (13 lb-ft)
Oil drain plug: 35–40 Nm (26–30 lb-ft)
The Honda B20A5 engine was primarily used
in:
- 1988–1991 Honda Prelude (North American market)
- Select international Prelude models using high-output non-VTEC DOHC
engines.
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