Upgrading your Subaru

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Impreza
It is very rare that a Subaru Impreza is bought and left at the standard spec for very long.  Due to it's Rally pedigree the Subaru Impreza WRX and particularly Subaru Impreza WRX STi are bought by keen rally and performance enthusiasts and have a huge following around the world.  Because of this there are a plethora of parts suppliers and performance centres supplying everything from Hayward & Scott de-cat exhausts through Exedy multi- plate clutch kits front mount intercoolers, Whiteline suspension kits and Xenon Headlight Conversion Kits, a complete A-Z of performance parts.

Although some modifications are made to the body styling it is what is under the bonnet, under the car and under the wheel arches that counts. Upgrading the air filter to a Pipercross foam or Green Cotton or K&N panel filter to provide an uprated air flow can increase  performance by a few  horsepowers at relatively small  cost (£40-50).

One of the most common upgrades that is carried out is replacing the standard exhaust with an aftermarket one such as a . 

Ranging from a simple upgrade of replacing just the back box to give a nice shiny look and sound and a slight increase in bhp to a complete turbo back performance de-cat system (everything behind the turbo replacing the catalytic converters with a through pipe) to give an increase in performance.  An alternative to this is to fit a hi flow cat system which will still provide performance increase at just below a decat system but has the added advantage of keeping it street legal*. Replacing the exhaust system with performance upgrade high flow cat and decat can give around 20-25 bhp increase.

The real enthusiast however will be looking to really push up the performance from the standard 218bhp.  (All newer UK spec. STi models now come with a 265bhp engine, a six-speed gearbox, inverted suspension struts, Brembo brakes, front and rear limited-slip differentials, a faster steering rack, satellite tracking and a full body kit with high-rise spoiler). 

Further performance upgrades involve replacing the turbocharger for a larger aftermarket version, replacing the standard injectors and fitting an uprated fuel pump help to boost performance but at this stage remapping or replacing the ECU and fitting something like a Pipercross, Green cotton or Powertec induction kit & Front Mount InterCooler. Ceramic coating of the exhaust headers, up and down pipes and turbo to keep the heat down becomes desirable at this stage.

Fitting parallel fuel rails to avoid any lean running, equal length exhaust headers and further remapping of the ECU.  With all of this extra power comes additional torque.  The wise upgrader will also fit an uprated aftermarket clutch and maybe even change the gearbox gears to straight cut synchro and have the engine rebuilt with pistons, conrods, crank and shells and even having the block converted from open deck to closed deck or relinered with thick liners.

With all of this extra power comes the need to be able to stop efficiently.  Other common performance upgrades come in the form of uprated suspension and brakes.  Manufacturers such as Eibach and Whiteline produce enhanced performance adjustable suspension in the form of adjustable shock absorbers and anti roll (sway) bars and lowered springs.  Companies such as Brembo, BlackDiamond and Mintex produce a vast array of uprated products from drilled, grooved and combination brake discs to race track large 4 pot brake calipers and race track sport 6 pot professional calipers and brake pads of a varying degree of hardness.

Upgrading of the Subaru suspension is something that can benefit the handling of your now faster Impreza. Uprated Whiteline Anti Roll Bars and drop links is stage one. Many people just fit an uprated 22mm rear anti roll bar and front and rear drop links to improve handling but for a slightly stiffer approach fit the 22mm front anti roll bar and the 24mm rear anti roll bar and front and rear Whiteline alloy drop links.

A move away from standard shock absorbers to something like Kayaba stiffness adjustable shocks and Whiteline or Eibach lowering springs is something that can be undertaken on cars up to 2002. These are a reasonably good replacement fully 'on car' adjustable gas charged shock absorber for high performance cars.

Moving on to coilover suspension: This usually allows ride height adjustment by way of moving a large nut up and down the strut to raise or lower the spring and a separate adjustment for the stiffness of the shock absorber.

Whatever performance upgrade you are thinking of doing to your Subaru we suggest you do it incrementally rather than throw a lot of money at it all in one go.  If you upgrade something and don't like it you can reverse engineer but if you add a number of performance upgrades all in one go and do not like one of them you may have to reverse engineer more than one, such as exhaust and remapping if you decide to reverse the exhaust you may need to have another remap.

FAQ and How Things Work

*Beware the new MOT requirements that the noise of an exhaust must not be unreasonably louder than a standard exhaust in average condition. Also new legislation regarding fitting catalytic converters to cars registered after 1st March 2001. Cats fitted to these vehicles must be "type approved for the vehicle" for road use, therefore all aftermarket non "type approved" cats fitted to vehicles registered after this date must be considered for off road use only.