lastly, the adoption of an optimised piston skirt profile on which is deposited (screen-printed) a molybdenum bisulphate coating that allows piston/liner mating clearances to be pared to the minimum possible during production. This reduces noise produced by secondary movement of the piston in the cylinder (piston slap).

140 bhp 1.9 Multijet

In 2002, the Fiat Group introduced the second generation of Common Rail power units, 16 valve JTD engines with Multijet technology. The first of this new engine family in the world was the 140 bhp 1.9 Multijet, now making an appearance on the Fiat Stilo M.Y. 04 (saloon and Multi Wagon) paired with a 6 speed manual gearbox of sporty configuration.

This offers various advantages. The engine is quieter as it warms up. The improvement can be quantified as a reduction of 3 to 6 decibels depending on engine speed and environmental temperature. It is also very powerful (103 kW at 4000 rpm) and torque is generous (31 kgm at 2000 rpm). Despite these searing performance figures, the fuel consumption is low. The new power unit also reduces emissions even though it is not fitted with sophisticated exhaust gas treatment devices.

Now we will take a detailed look at the architecture of the new engine and, above all, the results achieved with the Multijet system and sixteen valves.

Power unit architecture

This engine is derived from the tried and tested 1.9 JTD 8 valve Common Rail unit and takes the form of a 4 cylinder in line unit with bore of 82 millimetres and stroke of 90.4 millimetres. The four valves per cylinder are driven directly by a twin overhead camshaft. The new turbodiesel has undergone several engineering changes to increase performance and engine torque at low speeds and to reduce noise levels and vibration.

For example, the Common Rail system used on the 1.9 Multijet 16v unit includes two new strategies for automatically calibrating and balancing the diesel injected to lower noise and reduce vibration.

Certain engine components are brand new: a cylinder head with hydraulic tappets, steel connecting rods and crankshaft, a piston with an internal channel to carry cooling oil to the main and connecting rod bearings that are made out of different material to the previous unit. The exhaust and intake manifolds are also new: the former is made out of a special high-strength material while the latter is made out of pressure cast aluminium.

The electronically-controlled EGR system is cooled by exhaust gas. The lubrication circuit has a new oil pump and an external heat exchanger (air/oil) for cooling the oil. The cooling system is fitted with a different water pump. This long series of improvements and changes have created a reliable, powerful engine with low fuel consumption.

The Multijet system

The adoption of the Multijet system makes the 1.9 JTD the first second generation Common Rail engine in the world. The underlying principles remain the same, i.e. high injection pressure and electronic injector control. But one extra feature has been added. During each engine cycle, the number of injections increases over and above the current number of two. In this way, the same amount of diesel is burnt inside the cylinder but in several portions to achieve smoother combustion.

The advantages include lower running noise, reduced emissions and a 6-7% increase in performance. All this comes with a level of engine efficiency that improves car handling still further.

These results are not to be underestimated, particularly because they are obtained with an engine that represents an incredible leap forward from prechamber diesels and even improves on first generation JTD engines.

The secret of the Multijet engine lies in the control unit that governs the electric injector opening and closure system (and also in the injectors themselves). The crucial part of the engine is the electronic control unit itself, due to its ability to deliver a series of very closely-spaced injections.

Fiat Auto's researchers developed the part (together with the injectors) especially for this application. It is designed to deliver the multiple injections that assure the designer more accurate control of pressures and temperatures developed inside the combustion chamber and also more efficient use of air taken into the cylinders.

This enables further goals to be achieved: quieter combustion, reduced emissions and increased performance. The Multijet system is underpinned by long years of research. Our engineers began by resolving the problem of limits imposed by the control units. Then they went on to map the benefits they could achieve by plotting different multiple injection sequences (two secondary injections very close to the main injection; one secondary injection not too close to the main injection plus two closely-spaced secondary injections; one secondary injection and then two main injections close together after a certain period etc.) against different engine service conditions: in the idling region; with low loads and low rpm; with high rpm and moderate load; with low rpm and high load etc.

The study revealed the potential of the system and showed that great benefits are achievable in all cases, though these tend to focus on one field or another according to the type of sequence chosen and the engine service area targeted. In some cases, for example, the priority is to reduce start-up times and fume levels, in other cases it is to increase torque and reduce noise while in others it is to reduce emissions and ensure a quieter drive.

And now this research strand has led to the creation of the first Multijet engine: another first for the Fiat Group in the diesel engine field. But we had been putting in a lot of hard work behind the scenes since 1986, the date that marked the arrival of the Croma TDI, the first direct injection diesel vehicle in the world.

At that time, this represented a true engineering breakthrough that was later adopted by other manufacturers. Direct diesel injection engines offered better performance and lower fuel consumption but failed to resolve the problem of excessive engine noise at low rpms and while speeding up or slowing down. So work began on a more advanced direct injection system and a few years later this led to the development of the Common Rail principle and the Unijet system.

The idea first came from the Zurich University research laboratories where scientists were working on an injection system that had never before been applied to a vehicle, i.e. the Common Rail system. The idea is simple yet revolutionary. If you continue to push diesel into a tank, the pressure inside will rise and the tank itself will become a hydraulic accumulator (or rail), i.e. a reserve of pressurised fuel ready for use.

Three years later, in 1990, the Unijet system developed by Magneti Marelli, Fiat Research Centre and Elasis on the Common Rail principle entered the pre-production stage. This stage was complete in 1994, when Fiat Auto started to look for a partner with superlative knowledge of diesel engine injection systems. The final stage of the project, i.e. completion of development and industrial production, was eventually entrusted to Robert Bosch.

Now our story has reached 1997 and the launch date of the Alfa 156 JTD with its revolutionary turbodiesel engine. Compared to conventional diesel power units, the JTD guarantees an average improvement in performance of 12% together with a 15% reduction in fuel consumption. These results meant that cars fitted with the engine were an immediate hit.

Now the time is ripe for the second generation of JTD engines, the Multijet and multivalve units: and the 1.9 JTD 16v multipoint engine was the forerunner of this new power unit family.

The advantages of multivalve technology

The new 1.9 JTD 16v power unit thus promises great power (103 kW) and generous torque (31 kgm). These results have been achieved by adopting a new engine setting, increasing the direct injection pressure from 1300 to 1400 bars and introducing a new turbocharger setting.

The power units are turbocharged via a Garrett turbocharger with variable geometry turbine that helps improve power delivery by allowing very high torque delivery even at low rpms. Suffice it to say that 90% of maximum torque is available between 1750 and 3250 rpm. These data translate into great driving satisfaction and truly inspiring performance.

The Fiat Stilo 1.9 Multijet 140 bhp (3 door) touches a top speed of 203 km/h (200 km/h for the 5 door and Multi Wagon), accelerates from 0 to 100 km/h in 9.7 seconds and covers a kilometre from a standing start in 30.9 seconds. Despite these searing performance figures, the fuel consumption is low: the saloon returns 7.6 l/100 km over an urban cycle, 4.2 l/100 km over an extraurban cycle 5.4 l/100 km for a mixed cycle, while the figures for the 5 door and Multi Wagon versions are 7.8 l/100 km - 4.4 l/100 km - 5.6 l/100 km respectively.

All engines available on the Fiat Stilo M.Y. 04 and the Selespeed gearbox

The new model offers a broad and diverse range of power units to enable all customers to find a Fiat Stilo M.Y. 04 with appropriate performance and fuel consumption levels. Now for a quick look at the other five engines: two turbodiesels and three petrol units.

1.9 JTD, 115 bhp

This power unit is a development of the tried and tested Fiat Auto Common Rail turbodiesel family. Certain refinements have been made to the original reliable, successful mechanical configuration to improve general engine behaviour and achieve high performance, low specific fuel consumption and even more effective emission control.

Turbocharging, for example, is managed by a new generation, variable geometry turbocharger. This unit benefits from being able to regulate the exhaust gas flow through a moving vane distributor (variable geometry) that optimises turbine operation at all times to ensure high engine flexibility at low speeds and a simultaneous increase in power and torque. These attributes are complemented by the familiar benefits of the Unijet Common Rail injection system.

It delivers a maximum power output of 85 bhp at 4000 rpm and offers a maximum torque of 255 Nm at 2000 rpm. A Fiat Stilo 3 door equipped with this engine touches 192 km/h (190 km/h with the 5 door version), accelerates from 0 to 100 km/h in 10.3 seconds (10.7 for the 5 door version) and consumes 5.3 l/100 km over a combined cycle (5.4 for the 5 door).

1.9 JTD, 80 bhp

The 59 kW (80 bhp) 1.9 JTD unit is the same as the 85 kW (115 bhp) unit from the viewpoint of architecture and operation. The only differences are that this unit lacks an intercooler and is fitted with a fixed geometry turbine instead of a variable geometry unit. It delivers 59 kW (80 bhp), available at just 4000 rpm, and a torque of 20 kgm at 1500 rpm.

A Fiat Stilo 3 door equipped with this engine touches 172 km/h (170 km/h with the 5 door version), accelerates from 0 to 100 km/h in 12.9 seconds (13.3 for the 5 door version) and consumes 5.4 l/100 km over a combined cycle (5.5 for 5 door).

1.6 16v, 103 bhp

The 76 kW (103 bhp) 1.6 16v unit has undergone structural changes to lengthen stroke and reduce bore. The result is lower fuel consumption, increased torque and lower weight.

When fitted with this engine, the Fiat Stilo 3 door can reach 185 km/h (183 for the 5 door). Acceleration from 0 to 100 km/h takes place in 10.5 seconds (10.9 in the case of the 5 door). The power unit consumes 7.3 l/100 km over a combined cycle (7.4 for the 5 door).

The improved thermodynamic efficiency (with the attendant fuel economy) is due, in particular, to a more compact combustion chamber, pistons that are 20% lighter and lower timing system friction: each valve now comes with one spring instead of two.

Combustion efficiency, on the other hand, has been improved by adopting a longer stroke that allows improved performance in general and increased torque at low speeds in particular (maximum torque is 145 kgm at 4000 rpm). Driving flexibility can only benefit.

Power unit weight is also reduced by 4 kg through changes to the following: crankshaft, pistons, crankcase, mountings and auxiliary components. The new flexible belt that drives the compressor makes the tensioner superfluous and ensures the component lasts as long as the engine itself.

The 1.6 16v 76 kW (103 bhp) engine also adopts a drive by wire electronic engine control device, that allows: a smoother drive, lower fuel consumption and lower emissions. Pencil coils also do away with the need for HT leads, reduce weight while ensuring the spark plugs last longer, more energy is available, cold starts are improved and on-board equipment is subject to less interference.

The 76 kW (103 bhp) 1.6 16v unit comes with a catalytic converter with high chamber density located in the engine bay that is active even when the engine is warming up.

1.8 16v, 133 bhp

The 1.8 16v power unit offers entirely respectable performance with a power output of 98 kW (133 bhp) available at 6400 rpm and torque of 162 Nm at 3500 rpm. This engine propels the Fiat Stilo M.Y. 04 along at 202 km/h (200 km/h for the 5 door) and allows the car to accelerate from 0 to 100 km/h in 9.9 seconds (10.3 for the 5 door). These results have been achieved through a series of improvements to improve mechanical efficiency (lighter drive components and adoption of a steel cylinder head gasket), reduce weight (some 3 kg less), decrease noise levels and reduce vibrations (the engine centre of gravity displacement has been reduced by some 10% by adopting a lighter piston).

The engine also comes with drive by wire throttle control. One reason it feels so flexible and satisfying to drive is a delivery curve that makes 90% of torque available at just 1800 rpm and stretches to over 6000 rpm. The credit also goes to certain technical solutions such as the sporty exhaust (close-coupled) and a variable geometry intake system.

Over a combined cycle, fuel consumption is 8.0 l/100 km for the 3 door and 8.1 /100 km for the 5 door.

170 bhp 2.4 20v

This engine tops the Stilo M.Y. 04 range in terms of power and performance. A development of the five cylinder engine family, this 2446 cc power unit packs a punch of 125 kW (170 bhp) at 6000 rpm and a torque of 221 Nm at just 3500 rpm. Top speed is 215 km/h and acceleration from 0 to 100 km/h takes place in 8.5 seconds. These statistics require no further comment and ensure that a Fiat Stilo M.Y. 04 fitted with a 2.4 20v engine and sequential gearbox is one of the liveliest performers in its segment.

To be more specific, the technical changes involved an overall improvement in engine efficiency, a reduction in weight (by some 3 kg, achieved by making changes to the crankshaft and pistons, intake manifold and tappet cover), reduction in vibrations and noise levels, adoption of a variable geometry intake manifold and an electronic throttle body. In particular, the electronic management system responsible for adjusting port length ensures the engine is highly responsive whether driving around town or out on the motorway.

The 125 kW (170 bhp) 2.4 20v comes with two catalytic converters (one in the engine bay, the other under the bonnet) and two lambda sensors.
To exploit the benefits of this smooth operator to the full, the power unit has been paired with a Selespeed gearbox with ratios geared to enhance performance without detracting from fuel economy. After all, low fuel consumption is essential for environmental reasons and also to ensure low running costs.

The Selespeed gearbox for the 170 bhp 2.4 20v engine

The 2.4 litre, 5 cylinder power unit is combined with a sequential manual gearbox with reduced transverse and axial dimensions and outstanding manoeuvrability. This good manoeuvrability is assured by two levers on the steering wheel or a clutch that acts as a joystick and is positioned between the seats. This solution is renowned for offering a sporty drive that is also convenient and safe.

Sporty, because the slick, crisp gear changes allow engine potential to be exploited to the full.

Convenient, because the controls are easy to use and less tiring than those of a conventional gearbox. The clutch pedal is absent and gears can always be engaged without the grating or binding that can eventually ruin a gearbox. Safe, because the steering wheel is under full control even during gear changes because you do not need to remove your hand to reach the selector lever.

The up and down controls are located behind the steering wheel spokes on the right and left respectively. The up controls are used to change up gradually during acceleration, while the down controls are used to change down during deceleration. The choice of speed is left up to the driver, who can use steering wheel controls or the conventional lever.

A button located on the central tunnel near the gear lever is used to activate AUTO mode, which delegates the choice of ratio to the electronic control unit. The ECU assumes full control of the transmission and the Selespeed operates in the same way as an automatic transmission to offer a more restful drive that is particularly appreciated when driving in town traffic. Even in this case, the driver can suggest a gear to the electronic control unit without having to leave AUTO mode.

An acoustic signal also indicates that reverse has been engaged and another warns the driver when he or she turns off the engine while leaving the gear in neutral or tries to start the vehicle with the gear engaged without pressing the brake pedal correctly. Another warning light comes on when hydraulic fluid pressure is too low.

The Selespeed system is also able to diagnose faults in its components. It sets itself automatically to AUTO mode when a fault is detected in the tunnel lever or steering wheel buttons. If the fault is of another type, it reduces its functions to minimum so that the driver can reach the nearest service centre in complete safety.