The 8AR-FTS engine has an open-deck, midi-skirt aluminum cylinder block with ‘spiny type’ cast iron cylinder liners cast in the block material. The engine block is equipped with a twin gear-driven counter-rotating balance shafts, fully balanced forged steel crankshaft, high-strength steel connecting rods, and lightweight aluminum pistons. Pistons are cooled by piston-cooling oil jets controlled by the ECM depending on external conditions to improve durability. There is a variable discharge oil pump increasing engine efficiency as well.
The cylinder head design of the 8AR-FTS includes an integrated four-into-two exhaust manifold. The exhaust manifold has two separate exhaust ports: one is for cylinders 2 and 3, second – for cylinders 1 and 4. The new aluminum cylinder head also has 16 valves and two overhead camshafts (DOHC) driven by a roller timing chain. The valvetrain got roller rocker arms and hydraulic lash adjusters for constant zero valve clearance. While the exhaust timing is adjusted by VVT-i, the intake camshaft rotation is controlled by Toyota’s ‘Variable Valve Timing – Intelligent Wide’ (VVT-iW). The combination of the VVT-i and VVT-iW allows the engine to operate in two different cycles – Otto and Atkinson cycles. According to engine speed, the engine switches between them for maximum fuel efficiency and power. The intake camshaft has additional 4-lobe cam driving a high-pressure fuel pump mounted on top of the cylinder head. The exhaust camshaft also does an extra job – it drives a vacuum pump.
The 2.0T 8AR-FTS engine has a twin-scroll turbocharger designed by Lexus (Miyoshi plant). Exhaust gases are supplied to the turbine wheel via two separate channels at different angles, providing the ability to eliminate a variable geometry mechanism, at the same time also a slight increase in efficiency. The maximum boost pressure is around 1.17 bar (17 psi). An air-to-liquid intercooler is mounted directly to the engine before the intake manifold. The engine speed is controlled by ‘Electronic Throttle Control System – intelligent’ (ETCS-i). Like the 6AR engine, the 8AR-FTS has combined fuel injection – direct injection into the cylinders and conventional port injection. The Lexus calls it as ESTEC D-4ST (Economy with Superior Thermal Efficient Combustion Direct injection 4-stroke with Turbo). Depending on engine speed, the system uses both types of injectors or direct injectors only.
As mentioned above, the 8AR-FTS is the first new gasoline turbo engine, released after a long period since the production of the 3S-GTE and the 1JZ-GTE. But the manufacturer didn’t stop on it and continued that series by a small turbocharged engine – the 1.2T 8NR-FTS.