FOCUS RS POWER

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At the heart of every great performance car is a great engine.  We’ve cut no corners in the development of the Focus RS engine.  This is a bespoke, high-performance powertrain.” Len Urwin, Powertrain Manager, Ford Team RS

The turbocharged Duratec RS 2.5-litre engine creates Focus RS’ distinctive character, delivering its peak power of 224kW at 6,500 rpm and peak torque of 440Nm between 2,300 and 4,500 rpm.

Power Generator

Pretoria, 25 August 2010 – The Focus RS engine shares its fundamental structure with that of Focus ST, but there the similarities end.  Powertrain manager Len Urwin knew from the beginning that simply adjusting the engine management system for more power would be insufficient for a true RS.

He explains: “There was never an intention to try to ‘chip’ the ST engine.  We evaluated several approaches using the ST engine and none gave us the combination of power delivery, character and durability that we wanted, so we opted to create an RS Duratec, using the ST unit as our base.”

The objective was increasing power and torque without affecting durability.  To meet that, multiple detail changes were made to the powertrain including a revised cylinder head gasket, ultra-durable metal sprayed cylinder bores, revised pistons and a bespoke camshaft profile and connecting rods, allowing bigger small end bearings.

However, the most obvious changes are the new intake system, exhaust manifold and turbocharger.  The larger Borg Warner K16 turbo fitted to Focus RS offers a maximum steady state boost pressure of 1.4 bar – double that of Focus ST’s 0.7 bar – to generate the car’s 35% power increase.

Committed to maintaining responsiveness of the engine, Urwin’s team focused on three areas:

  1. Integrating the turbo with the exhaust manifold, to allow subtle manifold tuning and strategically locating the turbo in the engine bay, to optimise crash performance and minimise revision to the exhaust system and associated oil and water pipes;
  2. Carefully sizing the required larger turbo, to closely match the ‘bottom end’ engine responsiveness of Focus ST;
  3. Reducing the induction system and exhaust losses.

Focus RS needed its own, more aggressive performance character so engineers also modified the torque ‘ramp-up’, to enhance performance feel when on boost.

“While we wanted to be equal on low-end responsiveness and minimise the common off-boost inertia of larger turbos, we didn’t want RS to have the same character as ST,” explains Urwin.  “We wanted a stronger feel of increasing boost; we wanted you to really feel the surge of the turbo.”

With the turbo spinning, power arrives quickly.  The 224kW peak is reached at 6,500 rpm and holds until the 7,050 rpm redline, to allow full use of the top of the power band.  After three seconds at this redline, the engine management system recognises no gear shift and then limits revs to the car’s maximum continuous running rpm of 6,500.

“Turbo engines with flat torque curves can often feel like they run out of steam at the top-end, but we wanted to reward drivers who took Focus RS to the red line,” states Urwin. “We’re really proud of the result – strong mid-range transient response and a free revving top-end.”

Straight Torque

However, Urwin believes that the power is unlikely to be the first thing drivers will notice, as to get to that redline they will have travelled along Focus RS’ 440Nm torque curve.

Offering more torque than any Ford RS production car before it, Focus RS’ torque curve has a steady state peak beginning at 2,300 rpm and running to 4,500 rpm, meaning torque can be appreciated in any gear and at most road speeds.   The 440Nm peak torque is a 38% increase over Focus ST.

Says Urwin: “Matching low-end responsiveness with a larger turbo and a peak of 440Nm is a real achievement.  That’s a figure you would only have seen in so-called ‘supercars’ just a few years ago.  It gives Focus RS a gutsy, strong pull at the lower end of the rev range – great for those wanting a powerful performance feel but also great for more relaxed everyday driving.”

Bespoke Transmission

That combination of performance ability and cruising capacity is made practical by a specially-developed, six-speed Ford RS transmission.  It shares its gear ratios with the Focus ST gearbox on which it is based, with minor modifications to bearings and clutch housing and a revised, stronger differential.

Overall, gearing is one per cent longer than ST due to the larger rolling circumference of Focus RS’ specially developed tyres – further evidence of the team’s attention to every detail.

This allows gearing long enough for Focus RS to reach the all-important 100 km/h barrier in second gear.

Differential Difference

Putting the torque on the road is aided by a Quaife helical limited slip differential.  The Quaife differential was first developed for the original, five-speed Focus RS in 2002, but revised and improved by Ford Team RS for the new, six-speed Focus RS.  Today, it features a sixth planet gear and has been revised for increased strength and a more subtle intervention and torque transfer.

Computer-aided engineering drove the design of the differential, identifying the potential areas for increased strength.  This was aided by measuring rig work and whole vehicle development, with particular attention to refining performance plots for the differential’s torque bias function, to maximise dynamic performance.

Concludes Urwin:  “We have tuned the differential for a progressive torque transfer.  Our work was focused on creating an optimum drive for both road and track, in the dry and the wet.  It was in finding this balance that our tuning efforts were directed.”

Cooling RS

Creating a high-performance version of the Duratec 2.5-litre with this level of power also required significant attention to its cooling ability.  The cooling strategy was two-fold:

  1. create a cooling pack that met the high performance requirements of Focus RS and;
  2. match this to a comprehensive aero pack that delivered the required volume of cooling air to the system.

Explains Urwin: “Around 80% of the external cooling for Focus RS comes through the car’s lower front grille aperture and its precise size, shape and mesh density were a critical part of our work with the Aerodynamics team.”

The lower front aperture is approximately 30% larger than that of Focus ST and none of the precious cooling air it collects is allowed to escape, thanks to carefully designed ducting.

This ‘upstream’ ducting focuses airflow channelled into the car’s main trapezoidal aperture by the front air splitter and front bumper form, with the exact shape dictated by many hours of research, including Computational Fluid Dynamics (CFD) and wind tunnel work.

Outboard trapezoids either side of the main intake are blanked off, but positioned to give the option of converting to additional cooling systems for serious track use.

A new, 25% larger capacity radiator keeps engine coolant and engine oil temperatures under control, even in the most committed performance driving, in combination with a larger, 14-plate, engine-mounted, water-cooled oil cooler.

The final part of the engine cooling picture is Focus RS’ signature bonnet louvers, which Urwin identifies as having a particular benefit: “The louvers help with idle cooling, especially after high speed running, such as on a circuit, so were an important addition to Focus RS.  They’re there for a reason.”

Testing of the cooling pack took place around the world, to find the broad range of required conditions, including Arizona, Southern Italy, the Austrian Alps and a variety of European race circuits.

“CFD helped us in the early stages of cooling development, but there’s no substitute for real-world testing.  We spent significant time testing physical prototypes, in wind tunnels and variety of real-world climate extremes to perfect this work,” explains Urwin.

RS Breathing

The new intake system for Focus RS includes a new body-mounted airbox with a low-loss, cylindrical filter, revised turbo ducting, a modified hot charge duct, high-efficiency intercooler and new cold charge duct.  The airbox also has a unique, double intake entry system to reduce induction losses further.

Intercooling is critical in high-performance engines and the Focus RS intercooler system is new, larger and specially developed for the car.  It is capable of reducing air temperatures from 160 degrees Celsius at the compressor, to a maximum of 60 degrees Celsius at the intercooler outlet, in ambient temperatures of up to 38 degrees Celsius.

RS Exhaust

The sports exhaust system is also unique to Focus RS.  Focus RS uses a one-brick catalyst to enhance flow and reduce exhaust back-pressure, whilst meeting current exhaust emissions requirements.

The design of the turbo and manifold allows Focus RS to use ST’s exhaust geometry, downpipe and flex, with revised hangers to accommodate the car’s 20mm lower subframe.

The exhaust system also features a modified mid-section, with a revised, 4.2-litre mid-muffler, fitted around Focus RS’ larger, 62-litre fuel tank (up from 55 litres in Focus ST).  At the rear, a modified muffler uses two larger, 100mm-diameter, ‘trumpet’ tailpipes to further reduce pressure losses.

The entire system has been tuned to provide a sporty sound. Team RS engineers knew well that, for Focus RS customers, how the exhaust system sounds is as important as how it looks or performs.  Every Focus RS customer wants their car to sound ‘right’ and creating an induction and exhaust sound to fit the image and character of Focus RS was another critical aspect of its powertrain development.

Focus RS employs a ‘sound symposer’ system, to amplify selected engine frequencies and convey pleasing engine sounds into the cabin, contributing to that all-important RS performance environment.  As in all aspects of the engine, the symposer system has been adapted and tuned to fit the character of the vehicle, giving a raw, motorsport edge not present on Focus ST.

Urwin’s Powertrain team also created detailed performance characteristics to delight enthusiasts, such as a spark retard that encourages the pop and crackle in the exhaust on throttle lift.  Focus RS also has a distinctive, more aggressive idle tempo and engine note, to reinforce performance feel.

All these details were tuned to meet strict EU production car noise regulations and Focus RS’ own targets for fuel economy and durability.

Explains Urwin: “We’ve gone as far as we can for a production car.  In all of our engine development, we have to stay within EU drive-by noise limits, provide good overall fuel economy for the class and meet exacting durability and emissions standards – yet still create a high-performance engine with an attractive, sporty induction and exhaust noise.  Achieving that is all about balance and a tireless attention to detail.”

The Ford RS comes with a 5 year / 90 000km Service Plan and a comprehensive 4 year/120 000km warranty with service intervals of 15 000kms. Customers will also benefit from 3 years of Roadside Assistance and a 5 year corrosion warranty.