Project GD STI, Fixing all the Details!

There are a lot of small details involved with swapping an engine, especially when upgrading all of the system parts for higher performance.  These make the difference in the reliability and driveability of any project.  There is a difference between an engineered enhancement of a car and just throwing some parts at it.  Here are some of the many things we did to get our STI on the road and running well.  In fact, this is the summation of many years of us tinkering with this car, you can read all the long-term details here!

The OEM fuel pump wiring is known to be inadequate for higher-capacity fuel pumps.   i-Wire makes the fix for this simple with this plug and play fuel pump wiring kit for the STI.  i-Wire makes all sorts of awesome plug-and-play wiring solutions for Subaru.  Their wiring kits are super high quality with OEM connectors and quality Raychem wire and shrink tube.

Subarus are also known to have engine grounding issues.  In addition to the factory grounds, we used i-Wire’s grounding kit to assure a nice solid grounding.

To make tuning and data logging easier, we used i-Wire’s wide band 02 sensor kit.  It makes it so an AEM Electronics wide band simply plugs into the OEM rear O2 sensor wiring for an easy install.   i-Wire also makes a lot of little jumper harnesses to make custom installations a snap.  We used their jumper wires for the drive-by-wire throttle, as the Process West intake manifold moves the throttle body several inches more rearward, the i-Wire jumper was just what we needed.   We also used their jumper wires for the Map sensor when converting to speed density. With i-Wire we didn’t have to cut or splice a single wire from the factory harness for our installation.


  1. I don’t think you are correct about the surge tank being mounted higher than the factory one. It’s mounted lower than the top of the cobb AF box and the stock is mounted almost level with the top of the intake plenum.

    It looks nice no doubt but it’s not higher than the stock one.

    1. We had a stock STI in the shop that I could actually measure and you are right, the top of the OEM tank is higher. The bottom of the IAG tank when the hoses attach is higher than the OEM tank bottom. The main reason we used it is to clear the process west intake manifold. Thank you for pointing this out and I edited the story to reflect this.

  2. Hi Mike!
    Do you think the lack of increased NVH from the IAG mounts maybe because of the increased chassis stiffness from the Cusco bracing? It would be interesting to test this out with and without the braces.

      1. Apologies, I did not mean for you to test it yourself, as I am aware you must have a busy schedule. I was just thinking out loud as that would be an interesting data point to test in the future ( possibly by me ). I do appreciate theses awesome articles you and your team have put together for free and I am building my STi very close to your build which is why I love to geek out on this stuff 🙂

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