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
through Exedy multi- plate clutch kits,
intercoolers, Whiteline suspension kits and Xenon
Headlight Conversion Kits, a complete A-Z of performance
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 .
from a simple upgrade of replacing just the Subaru's 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 and removing the resonated centre pipe with a straight through pipe and replacing the back box with a high flow back box) and a remap to give a bigger 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 20-30 bhp depending on model.
The real enthusiast however will be looking to really push up the Subaru performance from the
standard bhp. (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 and a faster steering rack.).
power 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
Subaru performance upgrades come in the
form of uprated Subaru suspension and brakes.
Manufacturers such as KYB, Eibach, Superpro, BC Racing and Whiteline produce enhanced performance and adjustable suspension in
the form of adjustable shock absorbers and anti roll
(sway) bars and lowering springs. 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 or better still screwing the strut into or out of the base bracket and a separate adjustment for the stiffness of the shock absorber.
Companies such as KSport, Brembo, PerformanceFriction, BlackDiamond and Mintex produce a
vast array of uprated Subaru Brake products from drilled, grooved and
combination brake discs to race track large Subaru 4/6/8 pot brake calipers and race track sport professional
calipers and brake pads of a varying degree of hardness and efficiency.
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.
Commonly asked questions.
Will performance upgrades void my Subaru warranty?
Warranties are peculiar things with grey
areas so be prepared to have a fight on your hands with
your main dealer. Having said that there is such a
thing as the Magnuson-Moss Warranty Act
This is the US federal statute that governs warranties on consumer products and although this is an American law you could use the information contained in it to argue your case in this country. Basically, it states that your warranty cannot be
deemed void because of an aftermarket part (this would
include performance upgrades) unless the aftermarket
part caused the problem that the warranty claim is
about. For example, if you fit an aftermarket back
box to the exhaust and your shock absorber failed then
the manufacturer should not deny your warranty claim
because a back box should not affect the suspension.
However if you fitted an aftermarket high flow
performance exhaust and a remapped ECU and your turbo
failed the manufacturer could claim that the extra
stresses caused by the remap and high flow of air had
caused the failure. The grey areas come in the
form of possible links such as if you fitted the above
exhaust and ECU and then you had shock absorber failure
the manufacturer may try to claim that the additional
performance of the car put additional stresses on the
suspension. The law looks at what is reasonable to expect and while the law may
be on your side, the dealer service department may or
may not be.
What subaru performance tuning can I do to my Subaru Outback, Non turbo Forester/Legacy/Impreza?
The answer I am afraid is that there is very little that you can do to a non turbo car to make it go much better than standard. Naturally aspirated (N/A) engines draw in air for combustion under atmospheric pressure. As the piston moves down, the intake valve opens allowing the piston to suck air into the combustion chamber. How well the chamber is filled is called its volumetric efficiency.
A volumetric efficiency of 100% means that the combustion chamber is completely filled with air compared to the combustion chamber at static conditions. The volumetric efficiency of a naturally aspirated engine can never be higher than 100% as the combustion chamber cannot be more full than it is under static conditions due to the air pressure being the same inside the combustion chamber as it is outside. Its ability to fill the chamber is also greatly affected by how large the intake valve is, how long the intake valve is open for and how fast the engine is rotating. The faster the engine is rotating the faster the air is being sucked through the inlet valve aperture. Air can only pass through the aperture up to a certain speed (try blowing through a straw - the straw limits how quickly you can empty your lungs in the same way that a valve aperture restricts the flow of air into the combustion chamber).
To improve the performance of a Normally asperated engine, its volumetric efficiency needs to be increased as this is what allows more air to be ingested by the engine to create more power. Increasing the maximum RPM will also increase its performance.
To increase its volumetric efficiency requires changes to cam shafts (to allow the valves to open for longer), inlet tracts to allow the air to pass more freely, exhaust systems etc. Even so the increase in power will only be marginal as most engines are fairly efficient from factory. In terms of ease and performance compared to cost, a forced induction engine is best.
The performance of a turbocharged engine can be increased greatly just by increasing the boost or controlling where maximum boost is reached. Simple modifications such as larger exhaust systems and free flowing air filters can yield large power increases compared to doing the same modification to a N/A engine.
You could convert it to a tubo car by changing the exhaust, engine, wiring loom, ECU and adding a turbo but the time and expense of doing this would be prohibitively expensive and you would do better by buying a turbo version of the car.
What subaru performance tuning can I do to my Subaru Legacy T ?
There is only so far you can go with these early Legacys before you blow the engine. How much power did you want to go to? The early turbo Legacy UK was 200 bhp and the early Impreza UK was 210 bhp and you can probably achieved this by changing the exhaust and putting in a high flow air filter. Also the Legacy was a heavy car so may seem slow by comparison.
A decat or high flow cat (to keep it street legal and MOT passable) exhaust system and replacement hi-flow panel filter are the first steps to more power. Next you would be looking at replacing the engine management system with an aftermarket ECU and having it remapped to the car.
After this and you need to be considering replacing the fuel injectors and turbo, (and probably the inlet manifold to enable a front feed turbo to fit), the fuel pump and possibly fuel regulator and having the map tweaked.
Next you would be looking at rebuilding the engine (and probably gearbox) because it was not strong enough to take the pounding.
The questions are, how far do you want to go and how deep are your pockets?