Layout
The engine block is made of cast aluminium and is horizontally divided in height with the 4 main bearings. The final main bearing also acts as an axial bearing.
The lower half of the crankcase is laid out in a ladder frame layout, into which the main bearing caps are integrated. This design improves the rigidity of the crankcase.
The oil pan is bolted underneath the frame.
The front face of the engine is made up of a V-shaped cover, which finishes off at the bottom with the oil pan and at the tops with the cylinder head covers. It also houses the drive for the valve train.
This consists of two sprockets, each of which transmits drive from the crankshaft to two of the four overhead camshafts.
The tensioned side of each chain runs over a guide rail, while the slack side is tensioned under oil pressure.
The cylinder heads feature 4 valves per cylinder, which are actuated by the camshaft via roller cam followers. The roller cam followers run on hydraulic compensators which automatically adjust the valve clearance. Accordingly, no adjustments are necessary.
Lubrication system
The engine has a forced-feed lubrication system with an oil pan.
The oil pump is a G-rotor pump which is located at the front of the crankshaft and is driven by the crankshaft. It sucks in the oil through a pipe with a strainer in the oil pan.
A pressure limiting valve is integrated into the oil pump. Before the oil is passed to the lubricating points, it first passes through an oil filter and an oil cooler. Both are located on the left-hand side of the engine.
The oil cooler is connected via hoses to the coolant circuit and ensures that the engine oil cannot become too hot.
The following components are connected to the oil circuit: main bearings, big-end bearings, camshaft bearings, hydraulic valve clearance compensators. The remaining components are lubricated with splash oil.
Cooling system
The cooling system of the engine is a thermostatically controlled cooling system with a water-based coolant.
The coolant is pumped by a circulation pump through the coolant galleries in the engine block and the cylinder heads.
The pump is located on the rear side of the engine and is driven via a belt by the intake camshaft on the left-hand cylinder bank. The belt is tensioned automatically.
The coolant flows on from the engine block via hoses to the radiator, where the heat is dissipated to the passing flow of fresh air.
If not enough passing fresh air is available then, depending on the temperature, one or two electric cooling fans located behind the radiator in an air deflection frame are switched on.
The cooling fans are controlled by the powertrain control module (PCM) via a relay.
A coolant expansion tank is provided on the right-hand suspension strut turret in order to allow the coolant to expand as it heats up.
The cap is located on the top of the expansion tank. It features an integrated pressure limiting valve which limits the pressure in the cooling system to around 1 bar.
Differences to the 2.5L engine
In addition to its increased capacity, the following modifications all contribute to the increased performance of the engine:
- revised camshafts with greater valve lift and optimised valve timing
- optimised intake ducts
- reduced exhaust back pressure thanks to the new exhaust system
- improved air throughput thanks to the revised intake tract
- modified fuel system with a higher operating pressure (4,5 bar) and an increased delivery rate (80 l/min max.)
- revised calibration of the engine management system
In addition, measures have been implemented to improve the dissipation of heat in the system. The performance of the cooling system has been improved and the above-mentioned oil/coolant heat exchanger has been installed.
