Reflashing 101 – An Introduction

It wasn’t that long ago that tuning or remapping your factory car required an aftermarket ECU. Factoring in the cost of the ECU then installation and finally expert tuning adds up quickly. What if you are just adding a few bolt-on parts and want to get the best out of your stock engine without breaking the bank? Well if you have a late model Mitsubishi or Subaru then reflashing is the perfect solution!

Reflashing is a technique that allows modification of the factory engine management map through the vehicle’s diagnostic (OBD2) port. This allows us to alter the factory ecu mapping the same way that the factory engineers do it. There is no wiring required, none of the factory components are removed or changed and the factory map can be returned to stock at any time if required.
When compared to a full stand alone ECU, there are some pretty big benefits with reflashing as you can see below:

  1. Cost Effective – No need to spend thousands of dollars on a standalone ECU. Reflashing uses the hardware you already own.
  2. Discreet/invisible modification – There are no wires to cut, no sign that your ECU has been modified and you can always return to your stock map at any time.
  3. Retain factory driveability – With a reflashed ECU, your car will drive and start just like stock – This can be difficult to achieve with some standalone ECUs.
  4. Retain Factory Safety Features– Reflashing retains factory safety features such as knock protection, active knock control and dual octane maps for fuel and ignition timing – Great for peace of mind!
  5. Quick Turnaround – Reflashing can usually be performed inside a day, and we can also do the job while you wait if required.

Mitsubishi and Subaru reflashing: How it’s done

With aftermarket ECUs the manufacturer is kind enough to supply a nice convenient software package for the tuner to talk to the ECU and make tuning changes. Reflashing a factory ECU isn’t quite as easy and unsurprisingly Mr Subaru and Mr Mitsubishi aren’t too keen to help aftermarket tuners. The problem is all of the information in an ECU is stored as hexadecimal numbers and on its own this information is useless.

Using a software package called ECUFlash we can download the stock ROM data out of your ECU and use a ‘definition file’ to turn it into something useful and relevant which we can then manipulate to achieve the kind of tuning changes we want to make. ECUFlash is basically a graphical interface for the tuner, and the definition is a sort of map which defines the memory addresses where relevant information is stored.

Just as important is the scanning software which allows us to see what is going on inside the ECU. We use ROMRaider or EVOScan depending on the vehicle being tuned. The data from the scan log combined with information on our dyno lets us decide what changes are needed. We make the necessary changes using ECUFlash and then flash the new map into the ECU and confirm the changes on the dyno.

What Can You Expect From a Reflash?

Every model of car is different and so the potential for extra power varies too. In most cases a custom reflash on an otherwise stock car will offer gains of around 20 kW at the wheels which is a really noticeable increase. On some models such as the Mitsubishi EVO X which seems heavily de-tuned form the factory, these gains can be as large as 40 kW at the wheels, completely transforming the car.

The real value of a custom reflash comes once you have added some bolt-on parts to your engine such as an exhaust and intake. These parts can offer a significant increase in airflow and capitalising on this improvement with a reflash can easily see gains of 50-100 kW at the wheels!

No Limits Modification

Originally reflashing was something we would only consider for lightly modified vehicles as we were limited to many of the factory parameters and some of the factory hardware. With the advances in reflash technology though there is just about no limit to what can be run on a stock ECU.

Tuners stateside are now regularly turning out late model EVOs with 750 + kW (1000+ hp) using ECUflash and the stock ECU. To back up the dyno results, the fastest EVO drag car on a stock ECU has now run into the 8’s! This sort of performance would have been unheard of a few years ago.

Thanks to some extremely smart people in the EVO tuning community we now have the ability to ‘patch’ or modify the factory ECU code to achieve some really smart additional functions. Check out what can be done below:

  • Speed Density Tuning
  • Dual Maps
  • Flat Shifting
  • Live Mapping
  • Valet Mode
  • Flash CEL for Knock

Below are a couple of case studies which show what can be achieved with regular street cars:

Marc’s Mitsubishi EVO 9 Case Study

In stock form Mitsubishi’s EVO 9 is a great car but we always felt it was in need of a bit more punch. Marc agreed with us and came in for our Stage 2 upgrade package. This package is designed to optimise the performance of the factory engine and turbo without breaking the bank. This takes the power output to the limit of the factory injectors and the factory turbo and offers a great improvement in power and response.

The modifications we selected are listed below:


A typical EVO 9 will put out around 195 kW atw on our dyno. Once all the parts were fitted to Marc’s car, we got it onto the dyno and optimised the tune to suit. With the boost set to a peak of 1.5 bar (22 psi) we achieved 241 kW atw which is a gain of 47 kW peak and a massive 55 kW extra at 6800 rpm!

The upgrade is instantly noticeable on the street with a wide power band and fast response. Under full throttle the increased top end power makes the car feel like it just wants to keep on pulling. Under normal driving conditions the fuel economy is actually better than stock thanks to the more efficient intake and exhaust. Who says you can’t have the best of both worlds?

241kw at the wheels from a Mitsubishi Evolution IX

Daniels’ Subaru V10 STI Case Study

The late model STi is a great base for modification with a huge array of aftermarket bolt-on parts to choose from. Daniel’s car was already fitted with a 3” turbo-back exhaust, a FMIC kit and a Greddy Profec B boost controller when he brought it to but there are a few other areas which needed to be addressed to get to Daniel’s goal of 270 kW atw.

There are three main areas that hold back the STi in stock form are:

  1. Stock turbo will limit power to around 230-240 kW atw.
  2. Stock injectors and pump are only able to support around 230 kW atw.
  3. Stock MAF pipe can only flow sufficient air for 230-240 kW atw.

The modifications we selected are listed below:


We knew the injectors, fuel pump and turbo kit could easily provide the goods for over 300 kW atw on a built motor, but that is only half the package. To get around the limit of the stock MAF sensor, we used a larger diameter MAF pipe and then rescaled the output in the ECU to suit. After rescaling the MAF and configuring the ECU to work with the 1000 cc injectors, it came time to dial in the tune.

A stock V10 Sti will normally produce around 185 kW at the wheels on our dyno. Once the new parts were fitted and tuned, Daniel’s car punched out a staunch 268 kW at the wheels at 1.5 bar (22 psi) boost. The best part of the car is that it starts and drives just like a stock car. It is almost impossible to tell that any of the work has been carried out until you put your foot down. Once you do you better hang on though!

268kw at the wheels from Daniel's Subaru Impreza V10 STi

So is Reflashing for You?

Provided your particular model of car is supported, then there would be very few reasons not to consider a reflash in place of a full standalone ECU. Check out a list of our supported models below or send us an email for more information:


Mitsubishi EVO 5-10

Mitsubishi Airtrek

Mitsubishi VR4 (EC5A/EC5W)

Mitsubishi outlander

Mitsubishi Pajero Sport


Subaru Impreza WRX/STI V7-11

Subaru Legacy 2001-2011

Subaru Forester 2005+

Subaru Outback 2005+

Subaru Tribeca

5 thoughts on “Reflashing 101 – An Introduction

  1. Hi Michael,

    We have yet to perform a reflash on a Legnum. If you have a VR4 or a Legnum and are ready for a tune we would love to hear from you. Email me

    As an example a Version 7 STi with a 3″ exhaust gains around 30kW atw over factory.

  2. Pingback: Car Check: Subaru Legacy GT | Tune

  3. With the v10 sti above, did he have any internal mods? or was it just as listed? i just want to know how far i could go power wise in my v10 sti before stronger internals etc..

    • Marty, that STi has standard internals. We wouldn’t advise pushing to much more power out of the stock bottom end. It also depends what your intended usage is (track, drag, street etc). It’s always best to take your tuners advise, if you are Wellington local give us a call. 04 5866384

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