Opel A20NFT Specifications
| Engine Model: Opel A18XER |
| Engine Type: 4-cycle 4-cylinder SOHC 8-valve turbocharged liquid-cooled gasoline |
| Total Displacement: 121.9 cu.in (1.99 L) |
| Rated Engine Power: 150 Hp (110 kW) at 5600 rpm |
| Fuel System Type: Bosch Jetronic multi-point fuel injection |
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The Opel A20NFT is a 2.0-liter,
inline-four-cylinder, single overhead camshaft (SOHC), 8-valve,
turbocharged gasoline engine. It is part of the "Family II" or
"C20NE/L20" engine lineage, specifically representing a turbocharged,
low-pressure variant developed primarily for the European market in the
late 1980s and early 1990s. This engine was Opel's response to the
growing demand for forced induction performance while maintaining a
degree of fuel efficiency and reliability.
Based on the robust cast-iron architecture of the naturally aspirated
"Family II" engines, the A20NFT features a Garrett T25 turbocharger, an
air-to-air intercooler, and Bosch LE-Jetronic fuel injection with a
separate ignition computer. Its design philosophy emphasized broad,
usable torque rather than peak Hp, delivering strong mid-range pull
suitable for both performance and touring applications. While
technologically simple by modern standards, it is renowned for its
sturdy construction, tunability, and distinctive character. The engine
is a symbol of Opel's performance engineering in the era of analog
turbocharging, powering some of the brand's most iconic sport models.
Engine Family / Model: GM Family II / "C/L 20" Series, Model A20NFT
(also known as C20LET in high-performance form; the NFT is a
lower-pressure variant).
Engine Type: Inline-four cylinder, transverse-mounted, four-stroke
cycle, water-cooled, turbocharged and intercooled gasoline engine.
Fuel Management: Bosch LE-Jetronic (LH-Jetronic in later versions)
multi-point fuel injection with a separate ignition control unit (ICU).
Aspiration: Forced induction via a Garrett T25 turbocharger with an
internal wastegate and an air-to-air intercooler.
Bore: 86.0 mm / 3.386 inches.
Stroke: 86.0 mm / 3.386 inches.
Displacement: 1,998 cc / 121.9 cubic inches.
Compression Ratio: 8.5 : 1 (lowered from naturally aspirated versions to
tolerate boost).
Firing Order: 1-3-4-2. Rotation Direction (from front/timing belt end):
Clockwise.
Maximum Power Output (DIN): 110 kW (150 Hp) at 5,600 rpm.
Maximum Torque: 240 Nm (177 lb-ft) at 2,600-3,600 rpm.
Boost Pressure: 0.55-0.65 bar (8.0-9.4 psi). Redline: 6,200 rpm.
Fuel Requirement: Premium unleaded gasoline (98 RON / 93 AKI) required
to prevent detonation under boost. Emissions Compliance: Euro 1
standard.
Construction: Cast iron, with a deep-skirt, strong design derived from
the ubiquitous Family II block. This heavy-duty construction provides
excellent durability to withstand the increased thermal and mechanical
stresses of turbocharging.
Cylinder Bores: Integral (parent bore) in the casting. Standard bore
diameter is 86.00 mm (3.386 inches). Crankshaft: Forged steel
crankshaft, supported by five main bearings. Main journal diameter is 60
mm (2.362 inches). Crankpin diameter is 52 mm (2.047 inches).
Main Bearings: Steel-backed, tri-metal (lead-bronze) or aluminum alloy
shell bearings.
Pistons: Forged aluminum alloy (or high-quality cast) with a dished
crown to achieve the lower compression ratio. Features oil cooling
galleries fed by squirt jets from the block.
Connecting Rods: Forged steel, I-beam design, reinforced compared to
naturally aspirated versions.
Oil Pan: Stamped steel oil pan. Some high-performance applications may
have a baffled pan.
Construction: Cast aluminum alloy, cross-flow design.
Valve Arrangement: Single Overhead Camshaft (SOHC), driven by a toothed
timing belt. Two valves per cylinder (8-valve total). Valves are
actuated via rocker arms.
Combustion Chamber: Hemispherical ("hemi") design, a signature of the
Family II head, promoting good airflow and combustion efficiency. Valve
Seat Angle: 45 deg.
Valve Diameter: Intake: 41.0 mm (1.614 inches). Exhaust: 35.0 mm (1.378
inches). These are large valves for a 2-valve head, contributing to good
breathing.
Valve Springs: Single coil springs, potentially uprated for turbo
application.
Valve Clearance (Cold): Adjustable via screw and locknut on the rocker
arms. Clearance: Intake: 0.20 mm (0.008 inches). Exhaust: 0.40 mm (0.016
inches). Critical to check and adjust regularly, as clearances affect
performance and can change with heat cycles.
Camshaft Drive: Toothed rubber timing belt with a manual tensioner. Belt
failure results in catastrophic interference engine damage.
Injection System: Bosch LE-Jetronic or later LH-Jetronic. This is an
early electronic fuel injection system using an air flow meter (AFM) to
measure incoming air.
Engine Control: Two separate control units: one for fuel injection (ECU)
and one for ignition timing (Ignition Control Unit-ICU). The ICU
receives signals from a knock sensor to retard timing under detonation.
Fuel Injectors: Electromagnetic, top-feed injectors.
Fuel Pressure Regulator: Vacuum/boost referenced, mounted on the fuel
rail. Base pressure is 2.5 bar (36 psi) without vacuum/boost.
Throttle Body: Single-bore, cable-operated. May include an idle air
control valve.
Air Flow Meter: Vane-type Air Flow Meter (AFM) mounted in the intake
tract before the turbocharger.
Turbocharger: Garrett T25 fixed-geometry turbocharger with an integral
wastegate actuator.
Intercooler: Front-mounted air-to-air intercooler to reduce intake air
temperature and increase charge density. Boost Control: Mechanical
wastegate. No electronic boost control solenoid.
Type: Full-pressure, force-fed wet-sump system. Critical for
turbocharger bearing lubrication.
Oil Pump: Gear-type, driven from the crankshaft (often via a distributor
drive gear).
Oil Filter: Standard spin-on canister type.
Oil Cooler: Engine oil cooler is standard, using engine coolant for heat
exchange. Essential for managing oil temperatures under sustained boost.
Turbocharger Feed and Drain: Dedicated oil feed line from the main oil
gallery to the turbocharger center bearing. A large, gravity-fed drain
line returns oil to the sump.
Oil Capacity (including filter): 4.5 liters (4.8 US quarts / 4.0
Imperial quarts).
Recommended Oil Grade: API SG/SH or later. Viscosity: SAE 10W-40 or
15W-50, high-quality mineral or semi-synthetic. Turbo-specific oils with
high temperature stability are recommended.
Operating Oil Pressure: At operating temperature: 200-400 kPa (2.0-4.0
bar / 29-58 psi) at 2,000 rpm. Minimum idle pressure: 100 kPa (1.0 bar /
14.5 psi).
Type: Pressurized, forced circulation system with specific provisions
for turbocharger cooling.
Water Pump: Centrifugal, belt-driven from the crankshaft.
Thermostat: Wax pellet type. Opening temperature is 82°C (180°F) or 88°C
(190°F).
Radiator Pressure Cap: 100-120 kPa (1.0-1.2 bar / 14.5-17.4 psi).
Coolant Capacity (engine + radiator, approx.): 7.5 liters (7.9 US quarts
/ 6.6 Imperial quarts).
Coolant Recommendation: Ethylene-glycol based antifreeze mixed with
demineralized water (50/50 ratio). Turbocharger Cooling: The Garrett T25
turbocharger on the A20NFT is oil-cooled only. It does not have a
water-cooled center housing like later designs.
Electrical System: 12-volt DC, negative ground.
Ignition System: Distributor-based electronic ignition, controlled by a
separate Ignition Control Unit (ICU). Uses a rotor, cap, and spark plug
wires.
Spark Plugs: Cold heat range, typically one step colder than the
naturally aspirated engine. Nickel or platinum. Gap: 0.7-0.8 mm
(0.028-0.031 inches).
Knock Sensor: A piezoelectric knock sensor is mounted on the cylinder
block, sending signals to the ICU to retard ignition timing if
detonation is detected.
Wastegate Actuator: A diaphragm-type actuator connected to boost
pressure, mechanically opening the wastegate flap at a preset pressure.
Length (from front of timing cover to rear of block): 650 mm (25.6
inches).
Width (over valve cover): 700 mm (27.6 inches).
Height (from oil pan sump to top of intercooler pipework): 750 mm (29.5
inches).
Dry Weight (engine only, complete with turbo/manifolds): 160-170 kg
(353-375 lbs).
Engine Oil and Filter Change Interval: Critical. Every 7,500 km (4,700
miles) or 6 months under normal service. Severe service (frequent
boost): 5,000 km (3,100 miles). Always allow the engine to idle for
30-60 seconds before shutdown to allow the turbocharger to cool and oil
to circulate. Spark Plugs: Replace every 20,000-30,000 km (12,400-18,600
miles). Inspect for signs of detonation or fouling.
Timing Belt: Replace every 60,000 km (37,000 miles) or 5 years. This is
an interference engine; belt failure causes severe damage. Replace
tensioner and idler pulleys concurrently. Valve Clearance Adjustment:
Check and adjust every 20,000 km (12,400 miles). Vital for performance
and preventing burnt valves.
Accessory Drive Belts: Inspect and adjust tension every service. Replace
as needed. Coolant Replacement: Every 2 years or 40,000 km (24,850
miles). Air Filter: Replace every 20,000 km (12,400 miles). A clean,
high-flow filter is important. Fuel Filter: Replace every 40,000 km
(24,850 miles). Turbocharger Care: Ensure clean oil and filters. Listen
for bearing whine or excessive shaft play.
Cylinder Head Bolts: Two-stage torque procedure. Step 1: Tighten all
bolts in sequence to 40 Nm (30 lb-ft). Step 2: Tighten all bolts in
sequence to 80 Nm (59 lb-ft). Step 3: Final pass, re-tighten all bolts
to 80 Nm (59 lb-ft) in sequence. Use the specific sequence (center-out)
and ensure the engine is cold.
Main Bearing Cap Bolts: 80-85 Nm (59-63 lb-ft).
Connecting Rod Cap Bolts: 55-60 Nm (41-44 lb-ft) + 30-degree turn.
Flywheel to Crankshaft Bolts: 60-70 Nm (44-52 lb-ft) + 30-degree turn.
Crankshaft Pulley Bolt: 200-220 Nm (148-162 lb-ft).
Camshaft Sprocket Bolt: 80-90 Nm (59-66 lb-ft).
Spark Plugs: 25-30 Nm (18-22 lb-ft).
Oil Pan Bolts: 10-15 Nm (7-11 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Bolts/Nuts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold/Turbo Nuts: 25-30 Nm (18-22 lb-ft).
Cylinder Head to Exhaust Manifold: 25-30 Nm (18-22 lb-ft).
The Opel A20NFT engine was used in a select number of
performance-oriented Opel models in the late 1980s and early 1990s: Opel
Vectra A (1988-1995): The flagship performance model was the Opel Vectra
2000 4x4 Turbo (A20NFT), a sports sedan with full-time all-wheel drive.
This is the most iconic application. Opel Calibra (1990-1997): The early
turbocharged version of the Calibra, before the introduction of the more
powerful 2.0 16V 4x4 Turbo (C20LET), used the A20NFT engine, often in
front-wheel-drive configuration. This model is rare.
Opel Omega A (1986-1993): Available as the Opel Omega 2000 4x4 Turbo
sedan, sharing the drivetrain with the Vectra. The A20NFT is often
confused with or overshadowed by its higher-performance sibling, the
C20LET (DOHC, 16-valve, 150 kW/204 PS). The A20NFT is the SOHC, 8-valve
predecessor or lower-output variant. Its applications are specific to
certain model years and markets, primarily in Europe.
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