Standard car upgrade

A car is capable of yielding improvement even as standard, very noticeable improvements are available. Our own MY03 JDM STi in standard form gained 40 bhp and 45 ft lbs torque from just a remap. The major gain comes from enhanced throttle response and improved mid range punch. It is recommended that the fuel pump be upgraded since this is recognised as being prone to failure and/or weak performance even in a standard car. A STi of model year 2001 onwards cannot be remapped unless the fuel pump is changed.

Stage 1 upgrade

This is the first step on the tuning ladder and is the upgrade most people go for when looking to improve on the factory car’s performance.

Induction … high flow panel filter improves breathing by allowing greater airflow through the air box, capable of supporting up to 350 bhp.

Fuel pump … essential when any increase in performance is contemplated since the factory standard pump is weak and prone to failure, the failure mode is subtle since in the majority of cases the pump simply starts to deliver less flow into any given pressure demand causing lean running. The capacity selected should reflect the performance objective.
Exhaust system … there are two options at this level, A full decat from turbo back or a sports cat down pipe and decat mid/back section in addition. The sports cat should be a 100 cell item to ensure maximum gains whilst still remaining emissions friendly. Suitable systems are recommended to be three inch to allow for future upgrades however a good two and a half inch system would give similar results if this level is determined to be the limit of tuning aspirations.
There are several systems that could be recommended, for down pipes the Miltek sports cat is known to give good results. For the full decat down pipe then Janspeed or Hayward and Scott manufacture similar specification parts that give known good results. For the mid section and back box the HKS "Silent" is excellent with both Janspeed and H & S producing product that works well.

The remap, once again the remap of the factory ecu ensures that the best is gained from the above modifications and can bring from 60 to 80 bhp and similar torque improvements dependant on model and model year of car.

Fuel choice is very important and strongly influences potential gains, for the best opportunity then Shell V Power or Tesco Momentum (99) must be the norm. 97 ron Super is then next best with 95 ron allowing some gains but mainly forcing a remap for safe engine performance when using the low fuel grade. One fuel to avoid is BP Ultimate which is not suited to the Impreza engine.

Stage 2 upgrade, this assumes the engine remains standard

If a stage one tune has already been applied then the next steps are as follows.

Tubular headers … replacing the factory headers improves the mid and high rpm range performance, if fitted without map adjustment then the boost response is slower and boost creep can take place so the use of these is only recommended when the ecu is also adjusted to take full advantage. Note that it is important than the pipe diameters be sized according to the turbo in use, failure to take this into account can lead to turbo lag.

Induction … an induction kit replacing the factory air box allows even greater air flow and opens up the breathing, ideally complimented by an uprated air intake pipe to suit the chosen turbo option.

Stage 3 upgrade

If stages one and two have already been applied then the next steps are as follows.

Turbo … beyond stage two, the only way to further improve the performance of a car is to increase the turbo capacity, depending on the model year and model, there are a variety of options that could be considered taking account original turbo specification. All standard Impreza variants are capable of supporting up to 400 bhp providing that the right supporting modifications are employed. To achieve this level would require the use of a hybrid turbo and this could be installed to the normal factory position.

Alternatives can be used however it is prudent to check what experience of use is available to validate any manufacturer’s or suppliers claims.

Fuel Injectors … if the turbo is increased in capacity then the injectors have to be increased in capacity also to match.

The above are standard sized injectors readily available from sources such as Lateral Performance or Roger Clark Motorsport, larger sizes may be used but their suitability should be checked with our experience before purchase.

Front mounted intercooler … the factory fitted top mount intercooler is not recommended for use at 400 bhp, the MY02 onward STi top mounted intercooler and bonnet scoop/under bonnet tray is the best combination and can be used however some necessary compromises in the remapping process will be required to ensure safe use which may preclude the car achieving the desired performance level.

An efficient Front mounted intercooler overcomes the above limitation and allows optimum improvement using more advanced ignition timing and leaner fueling.

Recommended Front Mounted Inrtercoolers
The remap, bearing in mind the engine is still standard, great care must be exercised since over optimistic tuning can lead to engine damage. Our experience of this upgrade level is extensive.



MAF-Less System

By using a speed-density control strategy, the Mass Air Flow meter, and it’s associated limitations and potential problems can be removed. The ECU can be configured to operate with the OEM MAP sensor or any commercially available 0-5V sensor.

Real Time Live Mapping

All SimTek ECU’s can be real time live mapped providing your tuner with a constant stream of information. There is no need to stop the engine whilst ecu changes are uploaded, and there is no limit to the number of changes that can be made. The effect of changes can be instantly evaluated.

Plug 'n' Play

All the SimTek ECU's have no need for 'adapter looms', and fit into the OEM case, providing a neat and reliable installation. This also allows for the vehicle to be easily reverted to the OEM ECU should the vehicle be sold. Some wiring changes are required to enable the use of remote switches to allow real time map switching.

Advanced Wastegate Control

The wastegate control system incorporates features commonly found on high end aftermarket boost controllers, thus eliminating the need for this additional expense. This includes engine speed and throttle angle 3D closed loop control, along with mappable gear by gear compensations to get the best boost response.


'Multi-Map' enables you to switch between two predefined maps. These maps are defined to suit a customer and his specific request. For example low-high boost, dual fuel (for example pump fuel and pump fuel plus octane booster) Changes in Fuel, Ignition & Boost can be made within each map set. They are 'full maps' not just a single modification, to a common base map. You can choose how you select your desired map, either using an add-on selector switch (allowing the maps to be changed 'on the fly' whilst driving) or by using the throttle pedal position at switch on.

Knock Warning

The ECU uses the OEM Knock Sensor to listen for 'Knock'. This is then fed to a Digital Signal Processor for analysis. If the D.S.P. decides that knock is detected, the Check Engine Light will be flashed to give the driver warning that engine damage could be occurring. Optionally the ECU can be configured to take corrective action in an effort to avoid damage. The detection levels are adjustable and can therefore be set to allow for engine normal background noise. By monitoring this information, your tuner can adjust each individual cylinder to eliminate knock.

Closed Loop Fuel Control

The ECU uses the OEM narrowband lambda sensor to give optimal fuel control in the idle / light throttle / cruise regions.  As an option, it is possible to connect a true wideband sensor via an external device such as the Innovate LC1.

OEM Drivability

The use of 24 x 24 fuel and ignition maps, gives unparalleled resolution and results in excellent road manners for light throttle driving. Advanced acceleration enrichment features give crisp throttle response even when using large injector configurations. Comprehensive starting strategies which are replicated from the OEM ECU, ensure 'first turn' starting in all conditions.

Anti Lag System

As a extra cost option, the ECU can have the ALS installed. Three ALS calibrations are available, allowing for 'Jacked Open Throttle' based systems as well as driver selected Hard / Soft modes. Air charge temperature is monitored by the ALS system to reduce the risk of engine damage due to high charge temperatures.

Launch Control and Full Throttle Gear Change

As part of the ALS cost option, the ECU has the ability to provide launch control and full throttle gear change (F.T.G.C. requires the use of a non-synchromesh gearbox to gain maximum benefit)

Gear Change Output (Shift Light)

The ECU provides a 'Shift Light' output to indicate to the driver the optimum point to change gear. The point at which the output is activated is gear dependant. The Check Engine light is used to indicate the change point but an external visual display could be used.

Multi Stage Engine Speed Limiter

The ECU has a progressive engine speed limiter using a combination of fuel & ignition cuts. This provides full over speed protection, whilst not giving a sudden loss of power.

Individual Cylinder Fuel & Ignition Trims

The ECU allows each cylinder to have it's own fuel & ignition 'trimmed' to compensate for small differences between cylinders. The Knock Sensor D.S.P. can not only determine knock but can discriminate which cylinder is the cause. This permits the engine output to be balanced so that all cylinders are performing equally.

Automatic Water Spray / Injection Control

On vehicles equipped with an intercooler water spray or aftermarket water injection system, the ECU can take control of this to provide closed loop charge temperature correction. Trigger levels are determined based on engine speed, throttle angle, boost pressure and air charge temperature.