In this blog post we talk about installing a turbo kit (or any forced induction path) onto a non turbo (NA) engine. We are referring to Subaru engines only in this post as every manufacturer designs their engines differently with their specific goals in mind.
Why would someone put a turbo kit on a non turbo engine?
The reason many people do this is they want a few extra horsepower out of their motor and have a tight budget. The second reason is that some people are intimidated by doing the full turbo engine swap and think this will be an easier solution. In our experience, doing the turbo kit on a non turbo engine ends up being either ineffective in gaining the horsepower goal, expensive due to the custom work involved, and generally leads to engine failure and a standard turbo engine swap in the long run.
The last, and maybe most common, is the "be different or unique" category. Although we totally understand this idea, we believe that you can be unique while starting with a proven platform and then making it your own.
What are the effects of installing a turbo kit on a non turbo engine?
We think a lot of the information/ideas that are applied to turbo kits or supercharger additions comes from the domestic platforms like Ford, GM, and Chevy. The difference here is that domestic engines are overbuilt while import engines are not. These domestic engines (think LS) can handle the extra horsepower when they are turbo charged or super charged because the manufacturer designed them that way. Japanese domestic market engines like Subaru are built with precision and designed for a specific horsepower number in mind. You can make a few extra horsepower with a non turbo engine by swapping parts like the air intake and exhaust but Subaru has pushed the NA platform just about as far as it can go, so doing a lot of extra modifications will likely lead to the engine failing.
Issues when doing a turbo kit on a non turbo engine:
1. Tuning – this is truly the biggest issue in our experience. There are no good tuning paths when going down this route. The stock ECU for NA cars is essentially non tunable (there are a few exceptions to this rule like the 06/07 2.5i) but even those are not tunable enough to do what you need to do. That means if you want to tune your engine for the turbo kit (which is necessary for a good result) the only option is utilizing a standalone ECU with a custom wiring harness.
NOTE: We get requests for a WRX ECU to run a NA-T application but the reality is that to get that to work it basically requires a WRX setup so it is cheaper and simpler to just go the WRX swap route at that point.
2. Cost – the turbo kit itself may not cost much. However, when you start looking at the custom fabrication needed the price of the project adds up quickly. Typically, people go down this path and either get stuck or the engine blows up and end up putting a turbo engine into the chassis so all of the money spent to put the turbo kit on the original non turbo engine ends up wasted. When calculating horsepower to dollar, it will quickly add up in favor of standard swap being cheaper per dollar than a turbo kit.
3. Overall Horsepower – Due to the known limitations of amount of boost that can be applied, the horsepower gain is going to be minimal. If you’re truly going for an increase of power, we would suggest starting with a turbo platform where there are more standard paths for upgrades, especially when it comes to tuning.
4. Support for the Build – Since you’ve created a custom engine, there aren’t a lot of people who will support it. This means when you call a company for help, they are far less likely to have an answer for you or willingness to dig into it.
5. Availability of Parts - In the early 2000s, there were a number of companies that had off the shelf turbo kits like AVO, but with the availability and simplicity of a turbo engine swap, these items are no longer sold. You can find odds and ends and piece something together but you will end up spending a bunch of money and time on something that is most likely going to break or blow up.
What does iWire recommend?
We recommend either sticking with basic mods of the NA engine or putting in a turbo engine. If you’re looking for more horsepower in your car, we recommend starting with a turbo platform. That way you start with a more common and reliable engine with easy modifications and updates that are supported by most automotive companies.