The Subaru Impreza - Part 5

The year 2000 version of the Impreza (the P2000 WRC car) adds even more sophistication to the technology used in previous cars. The center and rear differentials, although still active, are almost fully locked all the time. This results in a car that handles better at the limit, both on gravel and tarmac, but is less versatile in tight corners. A redesigned roll-cage further rigidifies the car's body. The 1999 version of the car introduced an electronically actuated accelerator (there's no cable linking the pedal to the inlet manifold anymore, this system is known as drive-by-wire). This device, in conjunction with the ECU has a non-linear fuel injection characteristic whereas classic butterfly systems always use linear airflow to position functions. Subaru now use a semi-automatic, sequential gearbox which is operated by switches mounted on the steering wheels (just like F1 cars). It took more than four years to develop and test the new gearbox which now seems a big advantage over those used in other cars. The driver doesn't have to leave the steering wheel to shift gears.

The Impreza in its WRC version

The year 2000 Impreza (the WRC versions) gear boxes were custom built at Prodrive. The company tried the XTrac boxes some years ago but had a big enough budget to develop its own gear box. Sequential gear boxes work much like the ones fitted in motorbikes.

You push the gear lever to switch to the lower gear and pull it to switch to the higher gear. Most rally teams use sequential boxes and Subaru were the last ones to join the club. Although Prodrive did test their sequential box years earlier they never homologated it with the FIA and it was only fitted in 1999 in the competition cars. Sequential gear boxes are more troublesome in cars than they are in motorbikes.

The high torque output of car engines is much more difficult to transmit and that's the reason why you see so many competitors having trouble changing gears after some special stages. By the way do not think that cars such as the BMW M3, Ferrari 355 F1 or the Alfa Romeo 156 have solved the problem. The "sequential" option on these cars is, in fact, a normal 5 or 6 speed gear box controlled by an hydraulic circuitry. The gear switching is still H-pattern based. A classic (real) sequential box (i.e. non H-pattern based) goes for US 30,000 and up from specialized companies such as XTrac. Quaife and Hewland.
A last word on sequential gearboxes: how do they compare to the classic dog-boxes used in top rally cars until recently? Well drivers say that after testing the sequential versions they will not go back to dog-boxes. I find that although the convenience of a sequential box is very important, not being able to "jump" gears (i.e. 6th to 2nd in one movement) may be an inconvenience. The time gained when normal shifting occurs is lost whenever gear "jumps" must be performed. The major advantage of sequential boxes, apart from the quicker gear shift, is that they free up the driver's left foot (more than classic dog-boxes do) since no use of the clutch is required except for engaging first gear. This fact enables those drivers that brake with the left foot (a driving technique introduced on early Saab 96S cars back in the late sixties and currently used by Kankkunen, Mäkinen, Sainz and many others) to be more efficient.

One can only compliment Subaru for offering the general public a car such as the Impreza turbo. In these days of speed limitations, emission controls, excessive passive and active "security" features Subaru were able to offer a package really destined to the car-loving driver. The Impreza was, up to recently, the only 4WD turbo charged pure breed to be commercially available almost everywhere.

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