What is a RobTune

I provide the service of adding an external eprom (aka “chip”) to the EJ20G ECUs which forces the ECU to run my tune in place of the factory tune. My tune is safer for lower (92/91) octane compared to the stock tune. In addition to being safer, it improves overall performance, modifies limiters, and adds new functionality. My tunes are typical "off-the-shelf" type meaning they are not modifiable short of chip replacement and they are a bit generic thus not truly optimized for a particular setup. The overall goodness of a factory ECU remains intact (cold starts, advanced knock feedback, closed loop operation, fault detection, altitude compensation, etc) which means it runs and drives as stock.

How does it work

Subaru was kind enough to leave a blank spot on the EJ20G ECU board for an off-chip Eprom. The first generation STis used this to add special STi tuned eproms to the standard WRX ECUs For the V2 STis, they stopped adding the extra chips and starting their own ECUs.  GroupN ECUs used added chip tunes as well. On the non-chipped factory ECUs, the main board needs to have an IC socket soldered to it and then the Eprom can be fitted.  Once the jumper J1 is cut  the ECU will run the code from the chip.  Subaru chose a non-standard Eprom that has been out of production for some time.  Old stock can still be found, but supplies are getting very short.

Available Tunes

Currently I offer two main tunes depending on the injectors used. My “440” tune is for the stock EJ20G injectors which are grey top (440cc/min) injectors. This tune is safe for running 16psi with the TD05 turbo. My “550” tune is uses the factory MY'04-06 STi/LegacyGT/ForesterXT yellow sidefeed injectors (actual flow is 525cc/min). This tune is good to 18-19psi on the TD05 before the stock MAF EJ20G begins to max out. It is important to note that the Ver 3/4 (EJ20K) cars also used yellow sidefeed injectors, but they are not the same and only flow 480cc/min and cannot be used. To go further ONLY the specific two types of Subaru injectors listed above can be used with my tunes. It is also important to note that there is a lot of misinformation on the flow rates of these injectors. To put it simply, ignore everything else you read and trust my numbers. If you want to debate, send me an email with your flow chart and then we can talk :)

Tune Details

My tune modifies the fuel and ignition tables to better suit 91/92 octane.  The factory JDM tables are too advanced in the midrange for our best commonly available fuel.  The result is a lot of negative learned (and immediate) knock correction.  This essentially punishes the entire operating range and the net effect is lower and inconsistent power.  Along with performance degradation is the danger of sustained and uncontrollable knock.  By modifying the ignition tables I have both reduced knock in the midrange and added more advance in the top end.  Given that however, my main tuning strategy is to not tune to the ragged edge.   This means the ECU still has a bit of room to learn more ignition advance with higher octane, meth injection, better intercooling, etc. The Subaru ECU is very flexible in attempting to achieve the most advance for the given knock conditions. In addition to the main tables, I also modify the ECU limiters; speed cut, boost cut, red line.  Where the limiters are set is up to you, but I will give my recommendations. The stock boost is raised, but I generally require the addition of a cheap manual boost controller, or an expensive electronic boost controller.

Added functionality

I have hand generated my own assembly code and patched it into the Subaru code (and yes I am quite proud of this) First, I have increased the aggressiveness of the ECU to add timing advanced based on lack of knock feedback. This means that when the ECU goes through its normal periodic algorithm for finding the max advance multiplier, it starts out more optimistic, and results in more consistent performance. I have added Launch Control (see how this works XXX) The last feature that I have added is a knock indicator that uses the stock Check Engine Light. When the ECU flags a real knock event and prepares to take action, the CEL will flicker giving the user a warning More info on the knock light is XXX. I also have been playing with removing error codes for certain situations. I consider this experimental at this point.

What kind of results can one expect?

My dyno results were 287HP, 261Ft-lbs at the wheels which estimates to 340 crank HP. Stock for this motor is 260crank HP. The mods at the time of this dyno run were;

  • '95 WRX motor swapped into '00 Impreza RS
  • My 550 tune with '04 STi 525cc injectors
  • Apexi AVCR @ about 18psi
  • 3" ebay downpipe + 3" Fujitsubo exhaust
  • Apexi intake
  • Ver2 STi TMIC with factory upgraded feedpipe.
  • '02 WRX coil packs
  • ’04 STi fuel pump


From the graph, the green plot is my final run. You can see the gigantic improvement made to midrange torque compared to my early baseline tune (red plot). The improvement came from work on the ignition maps. My knock indicator helped tremendously to chase down the over aggressive timing regions that were holding back the overall ignition timing. At the most, it was a 45ft-lbs difference! As a note, for all 3 runs that day the power would fall pretty consistently at 6600RPM. The dyno operator attributed to heat soak. It was 90deg in the dyno room and they didn't have a good way to keep the TMIC cool. As far as drivability goes, on my 60miles/day mostly highway commute I typically log about 25-27mpg. I have seen as high as 30mpg on long trips. I run a standalone on my MR2 so I can tolerate a lot of small annoyances in the name of performance. My wife cannot. The biggest testament to drivability is that when she is forced to drive my car, there is nary a complaint.

Do you have any user reviews?

Besides the direct positive feedback that I get through email, I have pulled together a few links to forum posts that I have seen. I


What are the purchase logistics?

There are essentially three options;

    1) Mail your ECU. I will fit the chip and send it back.
    2) Purchase an ECU from me and I will chip and send it back.
    3)Same as #2, but you send back a replacement ECU within 30 days. I will refund $120 for the core replacement.

My spare ECU stock fluctuates, so this options 2 and 3 are not always available

What do I need to do prior to the tune?


  • Your car needs to be running well. Any problems before the tune, will be problems (usually worse) after you turn the boost up
  • You need the matching components for the tune, i.e. the right engine with 8.5:1 or less compression ratio (JDM EJ20G Forester motor is 9:1), the matching injectors for the tune (cleaned and flow tested is ideal), the matching green label JECs MAF, a fuel pump that can flow enough for the injectors.
  • You will need an aftermarket boost controller. The reason for this is that the only way to setup the ECU boost control maps is to spend a lot of time on that specific car. Any variation in mods will cause boost control issues (slow response, spiking, overshoot, etc). I recommend a good ball and spring type MBC, or any of the popular EBC.
  • I highly recommend following my coil conversion thread; http://forums.nasioc.com/forums/showthread.php?t=1192028


What are my tune options?


  • Injectors___ (stock gray 450cc/min EJ20G or +04/05 Yellow STi sidefeed 525cc/min) *NOTE EJ20K yellow injectors are 480cc/min and are not the same
  • CEL knock indicator ___ (yes)
  • Launch Control ___ (yes)
  • - LC rev limiter ___ (5k)
  • - LC speed disable ___ (>2mph)
  • Boost cut - ___ any value up to 1.25 BAR *OR* completely off (for stock injectors,1.25BAR; for yellow STi injectors, completely off )
  • Max boost - Use an aftermarket boost controller. For gray injectors, set 16psi or below. For yellow injectors, set 18psi or below.
  • Speed Cut ___ (OFF)
  • Rev Limiter ___ (up to 7400 for standard WRX HLA heads. Stock is 7100)
  • Warm Idle ___ (suggest just leaving stock unless you have lumpy cams)
  • Remove CELs (elimination of code44 for BCS removal is now standard! )


end faq