“We had to move the vehicle forward and in particular upwards with engine performance. The goal was to give the car more than 150 kW,” says Ford TeamRS Director Jost Capito."When it comes to providing a solid basis for performance and torque, you can’t beat extra displacement, so cubic capacity was at the top of our wish list," said Hoffmann. "And since various competitors in its class are already ’highly charged,’ we also set about finding a turbocharger appropriate for the project’s needs."
Bore is a relatively small 83 mm, while the stroke ends up being relatively long at 93 mm. Hoffmann discounted the traditional stories about long-stroke engines not coping with high revs as unfounded in the XR5, thanks to the combined efforts of cylinders and turbocharger.
"The long stroke action doesn’t dampen the sporting dynamics of this engine in any way, and the whole package remains calm and collected. It keeps its cool when doing its job because the rev count stays well within civilised limits," says Hoffmann.
Peak power of 166 kW is realised at 6000 rpm and the maximum 320 Nm of torque is available from a user-friendly 1600 rpm through to 4000 rpm. Hoffmann explained the high performance levels of the XR5 were achieved without sacrificing reliability and durability. "At moderate engine speeds the mechanical loading of the crankshaft drive remains modest despite high operating pressures.The superb power development of the five-cylinder engine also ensures smooth running. Typically, high performance four cylinder engines can face noticeable second order inertial forces. The XR5 engine, with five pistons as well as five forged and finely weighted rods is not affected by them. The second-order inertial forces have been successfully cancelled out by two counterweights on each of the crankshaft’s pins," said Hoffmann.
While initial testing of the new Focus XR5 Turbo powerplant was achieving all its goals, the engine note was not matching its dynamic capabilities. A clever sound design was needed, and a touch of intake noise really brought the sporty Focus to life.
A purposeful rumbling at idle was easy to organise with late ignition timing in the idle phase," says Hoffman. But the five-cylinder’s sound became really convincing when the team ran a thin hose from the area between the charge air cooler and throttle valve right up behind the bulkhead, transmitting the powerplant’s definite respiration ‘live’ into the cockpit thanks to a sophisticated device dubbed “the symposer”. Working like a mechanical loudspeaker, this new element was calibrated to bring a gentle amount of engine intake sound a bit closer to the driver. "Now the interior acoustics almost give the impression of sitting in one of the Focus’ famous motorsport cousins. From the outside, however, the Focus XR5 Turbo still sounds civilized and refined."
Stability was a top priority when planning the engine’s light metal alloy cylinder block, which is screwed onto the ladder-shaped, cast aluminium bedplate, anchoring it like a rock. "This combination provides the six crankshaft bearings with solid support, which is of fundamental importance because of the high operating bearing loads of turbocharged engines," explained Hoffmann. "Well balanced thermal conditions around the five combustion chambers are assured by a tried and tested feature of racing engines: cross-flow cooling, which sends the cooling water broadside through the engine."
A drive belt powers two overhead camshafts actuating tappets controlling four valves per cylinder. The valves’ generous proportions of 31 millimetres (intake) and 27 millimetres (outlet) ensure effective gas exchange. Hydraulic adjusters on the drive wheel side of both camshafts can be continuously fine-tuned through 80 degrees of authority – by 50 degrees on the intake side and by 30 degrees on the outlet side. "The motive for this complicated adjustability is obvious: more useable torque, especially at low engine speeds makes for a more tractable power delivery and also reduces fuel consumption and delivers cleaner raw exhaust emissions over the entire engine speed range," said Hoffmann.
Controlling valve operation, ignition timing and calibrating fuel injection to improve power development are left in the capable hands of a Bosch ME 9.0 engine control system. Installing the five-cylinder, turbocharged engine into the relatively small engine space was made easier by its compact turbocharging system. The intake manifold and turbine housing are in a small unit that fits easily between engine and bulkhead, with a KKK K04-2080 D turbocharger unit providing pressure on the intake side. A heat exchanger placed in front of the radiator cools hot air exiting from the other end of the turbocharger from well above 150°C down to 60°C.
For all of its power, the XR5’s engine only needs a mild 0.65 bar of turbo pressure. "This rather gentle turbocharging, combined with a reduced 9:1 compression ratio, ensures a high degree of efficiency and, taking the engine’s performance into account, good fuel economy," said Hoffmann.
The end result of the work by Hoffmann and his team is an engine that stirs the emotions, with throttle reaction that is immediate and dynamic, pulling away eagerly even from the lower end of the rev band. "We were lucky to be able to access a superb 5-cylinder engine thanks to Ford Motor Company’s shared technologies approach," said Hoffmann. "Tuning that engine to meet the specific performance targets of the Focus XR5 Turbo was nothing short of a pleasure!"