• Brian Keene

Best Subaru Engine Swap Choice for your Chassis

Updated: May 17



In this blog post we go over our recommendations for a turbo Subaru engine swap based on the non turbo chassis type. If you have a turbo car you are looking to swap, we generally recommend replacing the long block and leaving the rest of the car intact. More about turbo to turbo or NA to NA swaps here - My Engine Blew Up, What Should I Replace It With?


One of the questions we get asked a lot is “What engine do you recommend for my swap/upgrade?”. And our response is always “What chassis are you putting the engine into?” Not all cars are created equal so the chassis type has a lot of effect on what engines can be swapped into the car. Below we have categorized different chassis types with our recommendation for the best engine swap.


Please note, all of these swaps take time, money, and effort. There will be mechanical changes as well as wiring changes. Click here to read our Subaru Do's and Don'ts tips for your project. Click here to learn How to do a WRX swap into your RS.


Some definitions:

What is DBW?

CANbus Explained

Which Subaru Engine Do I Have?


Group 1: Non Turbo, Non CANbus, Cable Throttle Chassis:

Cars:

93-04 Impreza

98-04 Forester

95-04 Legacy

96-04 Outback

02-06 Baja


This group of chassis has the most options for an engine swap because you can stick with cable throttle or you can upgrade to a drive by wire platform.


The engines we recommend for this group include:

JDM 2.0 Engines like the EJ205 or EJ207 (not the EJ20X/Y (learn more here)), USDM 02-05 WRX. Another set of good options would be DBW 2.5 liter models like USDM 06-07 WRX, USDM 04-07 STi, or USDM 04-08 Forester XT. If emissions are a concern in your area, you'll want to stick with a US engine for your swap.

Check out this blog with our full write up on “easy” engine swaps for these chassis.


Special case for USDM 2002-2005 WRX chassis. The JDM 02-05 WRX and STi models are simple plug and play options. More about these here. The USDM 04-07 STi, USDM 06-07 WRX, and USDM 04-08 FXT are great options but require a harness merge to run the upgraded 32 bit ECU and drive by wire.


Group 2: Non Turbo, Non CANbus, Drive by Wire Chassis:

Cars:

04-08 Forester

05-07 Impreza


For this group of chassis we recommend sticking with a DBW engine. You could swap in a cable throttle engine but you’ll lose some features (more about that here)


The engines we recommend for this group include:

USDM 04-07 STi, USDM 04-08 Forester XT, or USDM 06-07 WRX. Most DBW JDM motors need to either be converted to cable throttle (JDM Forester) or their ECU's are CANbus equipped which makes them difficult to swap (JDM EJ20X/Y) so we don't really recommend them for DBW chassis.


Group 3: Non Turbo, CANbus Equipped, Drive by Wire Chassis:

Cars:

05+ Legacy

05+ Outback

08+ Impreza

09+ Forester


When it comes to CANbus equipped chassis, it is incredibly difficult to swap in a new engine. There are just too many inputs/outputs on the CAN line that the car is generally unhappy when a new engine/ECU is installed. For these cars we recommend finding a similar year turbo donor car (for example a 2010 WRX for a 2010 Impreza or a 2012 Forester XT for a 2012 Forester) and putting all of the wiring and engine components from the donor car into the NA chassis. This would include rear harness, ABS pump, dash, HVAC, etc. Literally every component from the turbo car would need to be put into the NA chassis for it to work properly. Since you basically need a full car for this to work, we generally recommend just purchasing a turbo car and adding some mods to that. However, some chassis have sentimental value so we understand why keeping it alive may be more appealing than buying a new one.


The other option to keep a chassis alive is to just swap the long block and keep the rest of the wiring and ECU intact. More about this option here - My Engine Blew Up, What Should I Replace It With?


Non EJ Engine Choices:

Some may have noticed that we do not recommend any FA engines (2015+ WRX or 2014+ Forester) or any of the 6 cylinder engines (EG33, EZ30 or EZ36). The reason we do not generally suggest these engines for the average DIY project is the difficulty and expense to swap them. We've written in depth blog posts about both engine types so you can learn more about the pros and cons to see if it's a good engine for your project.


FA Engines: https://www.iwireservices.com/post/fa20-engine-swap

6 Cylinder Engines: https://www.iwireservices.com/post/2018/11/27/6-cylinder-subaru-swap


Some more information about 6 Cylinder projects:

6 Cylinder vs STi Comparison: https://www.iwireservices.com/post/subaru-engine-comparison-6-cylinder-vs-sti


iWire H6RS Build Specs: https://www.iwireservices.com/post/iwireh6rs-build-specs


A note about V1-4 JDM WRX and STi engines: We do not wire these engines up at this time due to the fact that they are non OBD2 which makes smog/emission impossible and tuning very difficult. When you factor that in with the lack of replacement parts it becomes hard to not only build these engines but maintain them as well. A better solution would be to use an engine with OBD2 compatibility to make your project simple.

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