The 2008 Canadian Grand Prix winner will be competing in the secondary WRC2 category in a car no match for the top-class World Rally cars.
In an exclusive analysis for AUTOSPORT, Citroen technical director Xavier Mestelan-Pinon explains the differences between Kubica's DS3 RRC and the DS3 WRC that will be fighting for outright victory in Faro with Mikko Hirvonen and Dani Sordo.
"This is what really makes the biggest difference - and the difference comes from the restrictor on the turbo. On the RRC, the restrictor is 31mm, on a World Rally Car it's 33mm, which means less power.
"When Robert is only on 50 per cent throttle, the power will be the same from his car as the WRC because the restrictor is not restricting so much, but when the throttle is 100 per cent, then he will have less power.
"While Robert will have less power than the WRC, the torque is similar [to a WRC] and, on gravel, it is, in my opinion, easier to drive a car with more torque – which might help him against some of the Super 2000 cars in the WRC2 class.
"The flywheel on the RRC is also 0.5kg heavier. When you have the weight of the flywheel higher, it's like you put more weight into the car – it gives more inertia to the engine. Basically, this means the car won't rev as quickly or as freely as a car with a lighter flywheel. The power is the same, it makes the difference in the way the power is delivered."
"Here in Portugal there is no difference in the brake discs or calipers, but on asphalt there is a difference between the two cars. The diameter of the disc is smaller on asphalt and this means we cannot run the water cooling for the calipers.
"Talking about the brakes, one of the good things about Robert is that he is already using the left foot for braking in just the right way for the rally driver. This is impressive, he is a very instinctive and natural driver."
The rear wing
"The RRC has a smaller rear wing which means much, much less downforce and this is making a big difference now.
"When the cars are competing in the very high-speed sections, then Robert will notice a difference in how much the rear of the car slides.
"And we noticed this at the Fafe Rally Sprint last week, the smaller rear wing changes the way the car flies over the jump.
"Also, don't forget that while Robert's RRC has started its life as a World Rally Car before having the changes made, it wasn't the latest specification of WRC. In areas like the hub carriers and the damper, this is not the latest specification, it is running the previous spec, from late last year."
"The paddle shift is not the same system we have used before. The paddle itself looks similar, but it is longer than the one we used on the C4 and it is on the other side [of the steering column]; here it's on the left and in C4 it was on the right.
"The system on this car is cheaper. The other manufacturers don't want for us to use the C4 system because it's too quick. The system we use looks like the system we use to disconnect the rear axle when the handbrake is pulled. The gear shifts in 50 milliseconds, which is actually slower than you could make a manual shift. This does not earn him time.
"It's not just the paddle which is a bit different in Robert's car. The handbrake on his Citroen has to be pushed to make it work, instead of being pulled – this makes it easier for him."
AUTOSPORT explains WRC2
This is a new-for-2013 category, meant – as the name suggests – to be the WRC's second tier. It combines the Production Car WRC and the Super 2000 WRC from last season.
Turbocharged 1600cc Regional Rally Cars, such as Kubica's Citroen and Elfyn Evans' Ford Fiesta, will be pitched against naturally aspirated two-litre Super 2000 cars such as the Fiesta S2000 and the Peugeot 207 S2000.
Also included in the WRC2 battle will be the conventional Group N motors such as Subaru Imprezas and Mitsubishi Lancers.