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Toyota 18R-G Specifications
| Engine Model: Toyota 18R-G |
| Engine Type: 4-cycle inline 4-cylinder DOHC liquid-cooled gasoline |
| Total Displacement: 120.1 cu.in (1.97 L) |
| Rated Engine Power: 110-145 Hp (82-108 kW) at 6400 rpm |
| Fuel System Type: Twin-barrel side-draft carburetors |
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| General Technical Data |
0The Toyota 18R-G engine is one of the most respected twin-cam engines produced by Toyota during the 1970s and early 1980s. Developed jointly with Yamaha, this engine represents a significant step forward in Toyota’s performance engine technology, being one of the first mass-produced DOHC inline-four powerplants in Japan.
The 18R-G was based on the durable 18R
single-cam engine but received a completely new aluminum cylinder head
with hemispherical combustion chambers and a crossflow layout designed
by Yamaha. Known for its smooth operation, robust construction, and
high-revving character, the 18R-G became an icon of reliability and
sportiness in models such as the Celica GT, Carina GT, and Corona GT. It
was produced from 1972 through 1983 and served as the foundation for
Toyota’s later twin-cam engines, including the 4A-GE series.
The Toyota 18RG is a 2.0-liter inline-four gasoline engine with a dual
overhead camshaft configuration and a displacement of 1968 cc (2.0 L /
120.1 cu in). Bore and stroke measure 88.5 mm (3.484 in) and 80.0 mm
(3.150 in) respectively, providing a near-square ratio that balances
torque and rev capability. Compression ratio varies among versions from
8.3:1 to 9.7:1 depending on the market and fuel quality.
Power output ranges between 110 and 145
horsepower (82–108 kW) at 6,400 rpm, with torque figures from 160 to 175
Nm (118–129 lb-ft) at approximately 5,200 rpm. The engine is naturally
aspirated, with twin dual-barrel side-draft carburetors—usually
Mikuni-Solex PHH 40 or 44 units—supplying fuel and air to the
hemispherical combustion chambers. Some later versions, such as the
18R-GEU, employed electronic fuel injection (EFI) with Toyota’s early
TCCS (Toyota Computer Controlled System).
The engine block is made of cast iron for durability, while the cylinder
head is aluminum alloy to reduce weight and improve heat dissipation.
The DOHC setup utilizes a chain-driven camshaft system, and each
cylinder features two valves—one intake and one exhaust—operated by
bucket-type tappets. The crankshaft runs on five main bearings, ensuring
smooth rotation and long service life. Pistons are aluminum alloy with a
domed crown, optimizing the compression ratio for power output and
efficient combustion. The firing order is 1-3-4-2, with counterweighted
crankshaft and balanced connecting rods to minimize vibration.
| Fuel System |
The standard 18RG used twin side-draft Mikuni-Solex carburetors, each feeding two cylinders. These carburetors provided excellent throttle response and were tuned for performance rather than economy. They incorporated a mechanical accelerator pump and adjustable main jets. In the EFI-equipped 18R-GEU, fuel was metered electronically through manifold-mounted injectors, controlled by Toyota’s early ECU based on manifold pressure and engine speed inputs.
Fuel delivery pressure in the EFI system averaged 240–270 kPa (35–39 psi). The fuel system included an electric pump in the rear, a pressure regulator, and a return line to the tank. The carbureted models relied on a mechanical diaphragm-type fuel pump driven from the camshaft.
| Lubrication System |
The lubrication system is a full-pressure type with a trochoid oil pump driven by the crankshaft. The system maintains an oil pressure of approximately 350 kPa (50 psi) at 3,000 rpm. Oil is distributed through internal galleries to the crankshaft main bearings, connecting rod bearings, camshaft journals, and valve mechanisms.
The engine holds approximately 4.0 liters (4.2 US qt) of oil with a standard oil filter, and about 4.3 liters (4.5 US qt) with filter replacement. A bypass-type full-flow oil filter is fitted. Recommended oil viscosity varies with ambient temperature, typically SAE 10W-40 or 20W-50 for moderate to warm climates. The oil pressure warning switch is set to activate below 30 kPa (4 psi). The lubrication system also serves the camshaft chain tensioner and timing gear with dedicated oil passages.
| Cooling System |
The 18R-G employs a water-cooled system using a belt-driven centrifugal pump, crossflow radiator, and thermostatically controlled coolant circulation. The total coolant capacity is about 7.0 liters (7.4 US qt). The thermostat begins to open at 82°C (180°F) and is fully open at 95°C (203°F). A viscous clutch fan or electric fan maintains airflow depending on vehicle configuration.
The cooling system includes a bypass circuit for improved warm-up and an overflow recovery tank in later models. The radiator cap is rated for approximately 88 kPa (13 psi). Proper maintenance of the cooling system is essential to prevent head warpage or gasket failure, as the aluminum head is sensitive to overheating.
| Ignition System |
Early carbureted versions employed a conventional breaker-point distributor with centrifugal and vacuum advance mechanisms. Later versions transitioned to electronic ignition with a magnetic pickup and igniter module for improved reliability and spark precision.
Firing timing is typically set at 10° BTDC at idle, with total advance around 36° at 3,500 rpm. Spark plugs are M14 type with a gap of 0.8 mm (0.031 in). Recommended plugs include NGK BP6ES or equivalent for carbureted models and BPR5ES for EFI-equipped engines.
| Electrical and Starting Systems |
The engine’s electrical system uses a 12-volt negative-ground configuration. The alternator output is 35–45 A depending on model year. The starter motor is a reduction type rated around 1.0 kW. The EFI variants feature sensors for manifold pressure (MAP), coolant temperature, and throttle position, feeding data to the ECU for mixture control.
| Other Systems |
The timing system employs a double-row roller chain with an automatic
hydraulic tensioner and guide rails. The chain drive ensures accurate
synchronization between crankshaft and camshafts, minimizing stretch
over time. The crankcase ventilation system uses a positive crankcase
ventilation (PCV) valve connected to the intake manifold, maintaining
internal pressure balance and reducing emissions. The fuel evaporation
control system (in later models) includes a charcoal canister to trap
fuel vapors, feeding them back to the intake for combustion.
The 18R-G family went through several versions to meet tightening
emission standards. The earliest 18R-G (1972–1975) used simple
carburetion and produced around 145 hp. The 18R-GU (1976–1978)
introduced emission control measures, including an air pump and EGR
valve, reducing output to about 125 hp. The 18R-GEU (1978–1983)
incorporated EFI and catalytic converters, producing 135–140 hp while
improving drivability and emissions. Despite these changes, the
essential character of the 18R-G remained—a robust, rev-happy engine
beloved by enthusiasts for its mechanical feel and sound.
| Dimensions and Weight |
The 18RG engine’s overall length is approximately 685 mm (27.0 in), width 650 mm (25.6 in), and height 700 mm (27.6 in). Dry weight is around 165 kg (364 lb) for the carbureted version and 170 kg (375 lb) for the EFI type, mainly due to additional sensors and wiring. The compact inline-four layout allows installation in a variety of front-engine, rear-wheel-drive vehicles without major modifications. The DOHC head adds height compared to the standard 18R engine but provides substantial breathing efficiency.
| Maintenance Data |
Routine maintenance intervals are generally every 5,000 km (3,000 mi) for oil and filter changes under normal conditions. Valve clearance inspection is recommended every 10,000 km (6,000 mi), with cold clearances of 0.20 mm (0.008 in) intake and 0.30 mm (0.012 in) exhaust. Timing chain tensioner adjustment should be checked at 20,000 km (12,000 mi) intervals.
Spark plugs should be cleaned or replaced at 10,000–15,000 km (6,000–9,000 mi). The air filter element is to be replaced every 20,000 km (12,000 mi) or more frequently in dusty environments. Coolant replacement is recommended every two years or 40,000 km (25,000 mi). For EFI-equipped engines, the fuel filter should be replaced every 30,000 km (18,000 mi).
| Tightening Torques |
Cylinder head bolts: 83–87 Nm (61–64 lb-ft)
Main bearing cap bolts: 78–82 Nm (58–60 lb-ft)
Connecting rod bolts: 49–54 Nm (36–40 lb-ft)
Flywheel bolts: 88–93 Nm (65–69 lb-ft)
Camshaft sprocket bolts: 45–50 Nm (33–37 lb-ft)
Crankshaft pulley bolt: 160–170 Nm (118–125 lb-ft)
Spark plugs: 18–22 Nm (13–16 lb-ft)
Oil drain plug: 35–40 Nm (26–30 lb-ft)
Intake and exhaust manifold nuts: 25–30 Nm (18–22 lb-ft)
| Vehicle Applications |
The 18R-G engine was fitted in a variety of sporty Toyota models between 1972 and 1983, primarily in the Japanese domestic market but also exported to select regions.
Key applications include:
– Toyota Celica 2000GT (TA22, RA25, RA28, RA40)
– Toyota Carina 2000GT (RA17, RA45)
– Toyota Corona 2000GT (RT104, RT114)
– Toyota Mark II 2000G (RX22)
– Toyota Corona Coupe and Liftback 2000GT
Some rally-spec Celica GT models also used modified versions of the
18R-G with high-compression pistons, performance camshafts, and larger
carburetors, producing over 180 hp in competition trim.
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