Ford Focus RS

A charged four-cylinder engine increases performance in the hot-hatch and all-wheel drive improves traction and dynamics

The industry may well be focused on reducing fleet average carbon emissions, but there are still development programmes that place the emphasis on performance. And that’s important, because without these types of projects the industry loses a little of its mojo.

Hitting 100km/h in less than five seconds, maximising traction in a car with an output of 257kW/440Nm, and giving drivers the ability to drift in an all-wheel drive hot-hatch might not be a priority for many OEMs, but without these types of halo vehicles the more efficient, higher-volume variants may not sell as well. And it gives engineers something to enthuse about.

Perhaps no one was more enthusiastic about developing the third-generation Focus RS than Tyrone Johnson, vehicle and engineering manager for Ford Performance. His background includes Formula One and the World Rally Championships, and it was his influence that brought perhaps the biggest change to the vehicle – the move to all-wheel drive.

“I decided as soon as I came on board two-and-a-half years ago that I wouldn’t be sitting here if we didn’t do all-wheel drive,” he says. “I wasn’t interested to do another front-wheel drive vehicle.”

And for many, perhaps the limits of what could be achieved with a front-wheel drive set-up had been reached. In the previous generation vehicle, Ford’s engineers needed to develop the dual-axis strut at the front to cope with the hot-hatch’s 224kW/440Nm output from its charged inline four. The system eliminated the kingpin offset and gave more flexibility to tune the differential, which was needed for traction.

But all-wheel drive adds expense – that’s why many of the Focus RS’s rivals, such as the Mercedes-AMG A45 and Audi RS3, are premium vehicles – and senior management took a lot of convincing that it was the right direction for the latest generation of the car.

In fact, it was the eagerness of Raj Nair, Ford’s product development vice-president, that got the project the green light. “He’s the reason that this programme happened,” says Johnson.

Power and torque output have been increased to 257kW/440Nm – 470Nm on transient overboost – from the RS’s 2.3-litre turbocharged gasoline engine. That compares to the Mustang’s 228kW/434Nm.

Johnson says: “The engine started life as a 2.3-litre Mustang unit but we had to re-engineer the whole engine. The Mustang is a north/south installation, this is transverse, which means the intake, the exhaust, everything is new on this engine, but also internally we had to make a number of changes too.” 

Engineers integrated a low-inertia twin-scroll turbocharger with larger compressor to increase airflow, along with a much bigger intercooler to maximise charge density. The cylinder head is produced from an upgraded alloy material capable of withstanding higher pressures, while the cylinder block employs stronger high-tensile cast-iron liners.

The decision to increase the size of the intercooler did cause challenges further down the line, says Johnson: “We decided at the start of the programme just to go for the largest possible, we said bigger is better, but we had to introduce a blanking plate to make the system a little less efficient because otherwise it would create vapour in the intake system.”

The exhaust system was also a challenge. A large-bore exhaust system with an electronically controlled valve in the tailpipe helps optimise the balance of back pressure and noise output.

“That sound coupled with the pops and burbles that you may hear put us right on the limit of the homologation acceptance criteria,” says Johnson. “We had the homologation people in on three separate occasions to prove to them that we met all the requirements.”

But even with increases in performance, efficiency has been raised, and the Focus RS now emits only 175g/km CO2 and uses 7.7 litres of fuel to travel 100km on the NEDC test cycle. The previous generation managed 225g/km and 9.4litres/100km respectively.

The exhaust was difficult because of the introduction of all-wheel drive, which made having a straight system that helped reduce backpressure challenging because the driveshaft had to go through the same space occupied by the exhaust.

And it was the all-wheel drive system itself that was perhaps most difficult to get right. It might give you greater control over traction, but in high-performance compact cars half of the fun is dynamic ability, and a slight edginess to the controls. As Johnson says, front-wheel drive is good but has traction limitations, while all-wheel drive is good for straight-line traction but in terms of ultimate handling is limited.