Subaru Impreza STI Remapping

Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007

This article provides some information regarding tuning upgrades for WRX and STI Bugeye, Blobeye and Hawkeye, 2001-2007, including what’s required and performance expected. Please note that this article covers vehicles used on track or off-road and the examples are not legal for road use. If upgrading power also consider upgrades to suspension and brakes to support the power upgrade. Finally as per usual before we start, this is a guide only and you should carry out further research prior to commencing work.

A brief synopsis of this article is as follow, then read on for more information

  • WRX 2001-2005 2 Litre – Full Turbo-back Performance Exhaust System, Performance Uppipe, Upgraded Panel Filter, ECU Remap using EcuTek or similar – approximately 280 bhp / 280 lb/ft torque, using Shell V-Power 99 Ron fuel
  • WRX 2006-2007 2.5 Litre – Full Turbo-back Performance Exhaust System, Upgraded Panel Filter, ECU Remap using EcuTek or similar – approximately 280 bhp / 325 lb/ft torque, using Shell V-Power 99 Ron fuel
  • STI 2001-2005 2.5 Litre – Full Turbo-back Performance Exhaust System, Upgraded Fuel Pump to Walbro 255 lph or equivalent, Upgraded Panel Filter, ECU Remap using EcuTek or similar – approximately 330-340 bhp / 330-340 lb/ft torque, using Shell V-Power 99 Ron fuel
  • STI 2006-2007 2.5 Litre – Full Turbo-back Performance Exhaust System, Upgraded Fuel Pump to Walbro 255 lph or equivalent, Upgraded Panel Filter, ECU Remap using EcuTek or similar – approximately 340-350 bhp / 375-380 lb/ft torque, using Shell V-Power 99 Ron fuel
What BHP can I likely get by remapping a WRX 2001-2005?

By adding a Turbo-back exhaust system, exhaust up-pipe, high flow Panel Filter and ECU Remap you can achieve around 275-280 bhp on the 2.0 WRX 2001-2005, assuming its in good order.

What BHP can I likely achieve by remapping an STI 2001-2005?

With Turbo-back Exhaust system, high flow Panel Filter, Walbro 255 lph Fuel Pump or similar and ECU remap you can achieve around 330-340 bhp on a 2.0 STI 2001-2005, assuming its in good order.

What the approximate cost to get my WRX to 280 bhp?

Turbo back exhaust systems are around £600 upwards, depending on brand and quality, Panel Filters from around £35.00, Up-Pipes are around £150 and an ECU remap around £650, all plus installation costs.

Whats the approximate cost to get my STI to 330 bhp?

The STI will use the same Turbo back exhaust system as the WRX, so around £600 upwards for parts, there is no requirement for an Up-pipe on this model, but you’ll require a Walbro (or similar) 255plh Fuel Pump at around £85.00, a high flow Panel Filter at around £35 and ECU remap from around £650. Costs for parts only, so installation would be extra.

How much does an ECU Remap cost?

The price of an ECU remap varies greatly, depending on the mapper and the software remapping system they use. One of the best known systems is produced by EcuTek and their maps are priced at around £650 including an ECU license and the mapper times to load the map onto your Subaru’s ECU and adjust the settings.

Can I just add an exhaust and filter and not worry about the ECU remap?

Generally this is a bad idea, the ECU remap calibrates the ECU to the hardware you have fitted, such as exhaust, air filter, induction kit etc, and is adjusted to allow correct air / fuel ratios, ignition timings, boost targets and limits etc, so without an ECU remap, you risk damaging engine and not getting the most power out of the hardware upgrades.

WRX 2001-2005 2 Litre

WRX-300-600x390-1 Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
WRX 2003-2005 Impreza
  • Turbo-Back Exhaust System
  • Decat Uppipe
  • High Flow Panel Filter
  • ECU Remap

The 2001-2005 2 litre UK Subaru Impreza WRX models came out of the factory with 225bhp (for the later blobeye models) and although this makes for a quick car, some hardware and ECU tweaks can release more power for track use.

There are risks with upgrading the power on any vehicle and the Subarus are no different, so you need to bare in mind that this does put more strain on the engine, drivetrain and other components and as the cars get older and cover more miles the risk it likely greater.

The WRX 2.0 Models came fitted with a TD04 Turbo charger and whilst being fairly small this is good for around 275-280 bhp on average with supporting mods.

The car was produced with 3 catalytic converters at the factory and these restrict the power but are required for UK emissions and road use. If using solely for track use, these can be removed and replaced with stainless steel pipework for a much more free-flowing exhaust system and more power. Manufacturers such as Hayward and Scott, Cobra, and Scorpion all produce pipework options for model, with similar prices. Most are produced in 304 grade stainless steel and come with a lifetime warranty. Check out our exhaust system pages for this model aty this link https://scoobyparts.com/subaru-impreza-wrx-sti-exhausts/exhausts-for-impreza-wrx-sti-01-05

Assuming there are no seized bolts to the turbo, and all the original parts come away easily it likely will take around 2-3 hours to fit the Turbo back exhaust system and around 3-4 hours to fit the uppipe. However seized hardened turbo studs or sheared bolts when removing the original system can easily double this time.

Cosworth_Performance_Panel_Filter_Impreza_TurboWRXSTi_9207_714_7424 Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
Cosworth Performance Panel Filter

The standard panel filter should be upgraded to allow for much better airflow into the engine with a Performance Panel Filter such as K&N, Cosworth or Green, which can be found at this link https://scoobyparts.com/subaru-impreza-wrx-sti-performance-parts/air-filters-induction-kits-subaru-wrx-sti/subaru-air-filters-and-induction-2001-2007

These upgraded filters are a direct replacement for the original filter and take just a few minutes to install. See our link on Air Filters and Induction kits for more information on this.

Once these items are fitted, the car’s ECU needs remapping to calibrate it for the new hardware, which includes adjustment to ignition timing, air/fuel ratios and boost targets etc. This needs to be done by a professional, and a good place to start is by looking at www.ecutek.com then browsing to the dealer pages.

If the engine, drivetrain and other components are in good order, you should see power at around 275bhp and similar torque once completed, running on Shell V-Power 99Ron fuel.

The Gearbox is generally considered good for close to or around 340bhp, but obviously mileage and wear and tear will reduce this. Standard clutch is normally find for this power quoted here, but its worth upgrading to clutches such as an Exedy or Competition Clutch when the time comes. Link here for options https://scoobyparts.com/subaru-impreza-wrx-sti-clutches/subaru-impreza-wrx-clutch-flywheel-kits


STI 2001-2005 2 Litre

  • Turbo-Back Exhaust System
  • Walbro 255lph Fuel Pump
  • High Flow Panel Filter
  • ECU Remap
  • 3 Port Boost Solenoid (optional)
  • Induction Kit (optional)
STI-blobeye Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
Subaru Impreza STI 2003

The Subaru Impreza STI 2001-2005 2.0 litre ran a VF34 Turbo (2001-2002) models or a VF35 Turbo for 2003-2005 models and came out the factory at around 265bhp. With supporting modifications the STI was capable of 330bhp upwards, with some running closer to 350bhp.

Again, there are risks involved with this, so please read again the earlier advice on this. Also, as per previously mentioned, fitting a full Turbo back exhaust system removed the factory fitted catalytic converters, therefore is only suitable to cars used entirely on track or off road.

The upgrade path from, 265-330bhp is fairly straightforward. Firstly a full Turbo-back exhaust system needs to be fitted, this removes both factory fitted catalytic converters in the car. On the STI models there is no catalytic converter in the up-pipe from manifold to turbo, so no reason to replace this unless faulty or damaged.

A Turbo-back exhaust system costs from around £700 upwards and generally includes a downpipe, a centre section and rear silencer. Take a look at this link for options https://scoobyparts.com/subaru-impreza-wrx-sti-exhausts/exhausts-for-impreza-wrx-sti-01-05

Fitting time for the exhaust is around 2-3 hours, assuming no fitting issues are discovered.

Impreza-Fuel-Pump Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
Impreza WRX and STI Walbro Fuel Pump

The fuel pump needs to be upgraded to a Walbro 255 litres per hour unit (or similar) as the standard unit does not flow at a high enough rate. These can be purchased at this link https://scoobyparts.com/subaru-impreza-wrx-sti-performance-parts/miscellaneous-performance/walbro-fuel-pump-for-subaru-impreza-wrx-sti-2001-2007

Fitting time for the fuel pump is around 45 minutes. assuming no issues encountered during installation.

The final item required is a high-flow panel filter such as K&N or Cosworth, from around £35 upwards, see our filters page for more information https://scoobyparts.com/subaru-impreza-wrx-sti-performance-parts/air-filters-induction-kits-subaru-wrx-sti/subaru-air-filters-and-induction-2001-2007

Fitting on these is straightforward and takes just a few minutes.

Optional items such as a 3-Port Boost Solenoid and Induction kit can be considered prior to mapping, however we suggest speaking with the person you are tasking with re-mapping your ECU firstly to see if they consider these two items as a worthwhile upgrade at this stage,

Once all the hardware is fitted you’ll need to get the ECU re-mapped. As per earlier you could start by looking at www.ecutek.com and calling your nearest dealer listed on their dealers page.

If your engine is in good order, you’re running Shell V-Power fuel or similar 99 Ron and the car is correctly remapped, you should see figures of around 330bhp+ and similar torque. We’ve seen figures over 350bhp on this setup, but this is rare.


WRX 2006-2007 2.5 Litre

  • Turbo-Back Exhaust System
  • High Flow Panel Filter
  • ECU Remap
hawkeye-wrx Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
Impreza WRX 2.5 2006-2007

The WRX 2006-2007 has the same turbo as the earlier WRX but bolted to the newer 2.5 litre engine and as such makes for around the same BHP when tuned, but more torque. Power reaches around 280bhp with the components listed and torque is around mid 320 lb/ft.

Be aware though that in our experience we’ve seen more engine issues on this 2.5 litre model than the previous 2.0 litre models, with common issues such as Head Gasket failure and on occasion ring-land failure, both requiring an engine strip down and rebuild to rectify, so consider this before tuning.

The upgrade path is near identical to the WRX 2.0 however, with the model requiring a full turbo-back exhaust system, combined with a high flow Panel Air Filter such as K&N or Cosworth and an ECU Remap. Options over and above this include a Walbro Fuel pump, but we’ve not seen this to be a necessity at this level. As per before you’d need to run the car on Shell V-Power fuel or similar 99 Ron fuel to achieve figures quoted.

Its worth mentioning here that a full turbo-back exhaust system can become excessively loud and get you ‘black flagged’ from many tracks, so consider one of the Track Day exhaust systems made by Cobra or Hayward and Scott, such as at the following link https://scoobyparts.com/subaru-impreza-wrx-sti-exhausts/exhausts-for-impreza-wrx-sti-01-05/cobra-sport-3-turbo-back-track-day-exhaust-pack-sb31c-subaru-impreza-2001-2007-wrx-sti these have larger silencers built into the centre section to help keep noise down.


STI 2006-2007 2.5 Litre

  • Turbo-Back Exhaust System
  • Walbro 255lph Fuel Pump
  • High Flow Panel Filter
  • ECU Remap
  • 3 Port Boost Solenoid (optional, depending on performance of factory fitted solenoid)
  • Induction Kit (optional)
STI-hawkeye-2006-2007 Impreza Performance Tuning & ECU Remapping for WRX and STI 2001-2007
Impreza STI 2.5 Litre 2006-2007

The Hawkeye STI 2.5 litre model is able to reach around 340-50 bhp thanks to its larger VF43 Turbo and the the modifications listed, with torque in the range of 375lb/ft.

Like the other STI model listed in this article the hardware required is a full Turbo-back exhaust system (as per earlier consider the Track Day variety), a high flow Panel Air Filter such as Cosworth, Green or K&N, a Walbro 255lph Fuel Pump (or equivalent) and an ECU Remap. Optional are a 3 -Port Boost Solenoid (depending on whether the stock solenoid can control boost accurately and respond quickly enough) and an Induction Kit such as K&N or Cosworth, which can add to the power on some vehicles and sound great when gulping in air.

Again with this model we’ve seen the need to carry out Head Gasket repair and occasionally ring land issues, more so that the 2.0 litre models, so bear this in mind, especially when costs of doing so are around £1500 upwards.

Finally if you’ve got one of the already factory or dealer tuned Special Editions, such as GB270, RB320 etc consider whether its worth the expense to modify and tune the car, as the increase in power will obviously be less on the already tuned models and may affect future re-sale value if you can’t have your original factory ECU map reinstated.

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