The modern environmental rules forced the big changes in the engine cooling system of the engines. From the exhaust side, there is a stainless steel exhaust manifold (header) with integrated catalyst converter and EGR pipe. There is no restricted air in the intake manifold, in that reason the engine was equipped with a vacuum pump driven by exhaust camshaft to create enough vacuum in a brake booster. The engine has a simple fixed-geometry plastic intake manifold and electronically controlled throttle body - ETCS-i. The fuel pressure in the system is a range of 2.4-20 MPa. The multipoint fuel injection operates at low speeds and at mid-range together with direct injection. The low-pressure nozzles in ports have 10 holes. Each high-pressure fuel nozzle for direct injection has six holes and spray fuel at mid and high engine loads. The A25A engine has a combined fuel injection - in the combustion chambers (direct) and in the intake ports (multipoint). The head cover is made from polymer material. The exhaust camshaft has an additional cam for the high-pressure fuel pump. The electric actuator (VVT-iE) is used for the intake camshaft the traditional hydraulic VVT actuator was attached to the exhaust camshaft.
The A25A-FKS features the Dual Variable Valve Timing system (DVVT). The intake and exhaust camshafts are driven by low-friction single-row timing chain with a pitch of 8.0 mm. The engine is equipped with hydraulic tappets for continues zero valve clearance. The valves are actuated by camshafts via roller rocker arms. The intake port has a laser-cladded valve seat while the exhaust has a normal pressed valve seat. The angle between the intake and exhaust valve is 41 deg. The engine has an aluminum 16-valve cylinder head with two chain-driven camshafts in separate casing at the top. The main innovation is the second generation variable-pressure oil pump controlled by ECM electronics. The pistons are cooled with engine oil sprayed by two oil jets for each piston. The upper compression and oil rings have a DLC coating (Diamond Like Carbon).
The engine got the high-strength connecting rods and lightweight aluminum T-shape pistons with a special resin coating. That gear on the crankshaft drives the balancing unit attached to the engine block at the bottom. The crankshaft has 7 traditional counterweights and one with tooth gear. The longitudinal axis of the crankshaft has a 10 mm offset against the axes of the cylinders. The A25A engine has a new open-deck aluminum alloy cylinder block with sleeves cast directly in block material.
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