UPDATE AS OF JANUARY 2021. Unfortunately, iWire is no longer building harnesses for standalone ECUs to focus on stock ECU applications. Due to the fact the swap will not work 100% as it did from the factory, we can't put our name on this, so we no longer build harnesses for six-cylinder applications. Although some people have made it work with the stock six-cylinder ECU, there are several issues with this route that we are currently unable to solve (see below).
That said, below is still good information if you choose to do this yourself. Also, check out the Six Swapped Subaru group on Facebook for additional resources on six-cylinder projects.
The six-cylinder engine can seem like an excellent option for your Subaru swap because they are cheap, easy to find, and who wouldn't want more cylinders?! However, an inexpensive engine does not mean an inexpensive project. There are some crucial things to consider before starting this swap.
The first thing to consider is if you need to pass smog where you plan to register the car. If you need to pass smog, there are better swaps than this one. For most instances, this engine swap WILL NOT pass smog either due to lack of OBD2 functionality (EG33), check engine lights (01-04 EZ30D), or if it's attached to a standalone (recommended for all six-cylinder applications and required for 05+ DBW models). There is one example that will pass. If the car is a 1999-2004 Automatic Forester, Impreza, or Legacy, and you are running a 2001-2004 Automatic 6 Cylinder (EZ30D), then you can run the stock ECU, and the car can pass smog. Beyond that, if you put the six-cylinder into a manual car, there will be check engine lights and stalling issues since the stock ECU will not get the inputs from the automatic transmission it needs.
The second thing to consider is cost. While many six-cylinder engines are cheap, everything else needed to run the car will most likely be custom and, therefore, expensive. There are no off-the-shelf aftermarket parts, meaning most items must be fabricated. Custom items include the exhaust, engine mounts, radiator, fans, fuel system, etc. This is not a good swap for you if you don't have a big budget.
If you decide to proceed with this swap, we suggest using a standalone ECU. This way, you can get everything working from an engine standpoint, have tune-ability, and have the creature comforts from the factory. In addition, if you are looking at forced induction, the standalone can accommodate those upgrades. As mentioned, this setup will not pass smog because standalone ECUs will not communicate with an OBD2 scan tool.
Technically yes, the car will work. We acknowledge that people run a six-cylinder on the stock ECU if the car is older than 2004 and does not use CANBUS. We don’t wire this setup because the result does not work as it should from the factory, which means it's something we can't stand behind. If you want to use the factory ECU while acknowledging the potential issues and have the know-how or access to someone who does, go for it.
So overall, do we recommend doing this swap? For the average person who wants a simple upgrade in power, no. On the other hand, if you are up for a challenge and have the resources in money and mechanical know-how, it can be an enjoyable and rewarding project with excellent potential.
Our STi vs. 6 Cylinder Comparison can be watched below:
