Not all EJ205s are created equal.
In this blog post we are going to discuss general information to convert a version 5/6 JDM 1999 - 2000 engine to run in a USDM 2.0 WRX 2002-2005 chassis. This also applies to those doing a non turbo to turbo swap and have purchased a JDM V5/6 but want to run it with a USDM 2.0 WRX ECU. We have done our best to comment on all of the key components that need to change but depending on your project there may be some differences.
When would this situation happen?
There are a couple reasons, but the most common is purchasing the engine from an importer than was either mislabeled or the customer just didn't know exactly what to look for in a compatible engine for their application.
One option could be sending it back for a newer model EJ205 that is compatible with our USDM 2.0 WRX models. The easiest way to spot this engine is that it will have AVCS. More about the EJ205 differences can be found here.
If you have come across this blog and already have a JDM WRX that has AVCS this is a good resource for your next steps.
Why would I want to modify my V5/6 engine?
In it's stock form it would not plug in or run with in a USDM 2.0 WRX or with a USDM 2.0 WRX ECU in a non turbo to turbo engine swap situation
it's fairly straight forward to utilize the longblock with the mechanical changes described in this blog
For non turbo to turbo swap situations
The version 5/6 ECU was non-tunable and non OBD2, so getting it to pass any kind of emissions or BAR is would likely be impossible.
If you have any problems with the engine you can’t simply scan the code because of the non OBD2 platform.
Due to lack of tuning capabilities of the OEM V5/6 ECU you will not be able to make the needed adjustments to new parts which only creates issues, not more horsepower.
When it comes time to do repairs, finding parts can become difficult because in most cases the unique parts on the Version 5/6 engine have been discontinued and are difficult to come by in good usable condition here in the US.
Wait, I thought the JDM V5/6 ECUs were OBD2. They have an OBD2 Port right?
Alright, you caught us over simplifying. As byproduct of a communication difference it essentially renders the ECUs that come in these JDM models non OBD2 in our geographic region. Yes, the V5/6 models do have an OBD2 port that does communicate with the ECU. However, in 1999-2000 the protocols for communication were different in Japan than in the North America so our scan tools and tuning software can't read the information because they were not designed to do so.
Can I convert my V1-4 engine to run with a USDM WRX platform?
Unfortunately no. This does not work because the V1-4 platforms are phase 1 so the parts that are required to be swapped over do not fit.
USDM 2.0 WRX
What needs to be changed mechanically to get the engine work in my USDM 2.0 WRX or work with a USDM 2.0 WRX ECU with my non turbo to turbo Swap?
From a basic standpoint, you will only use the longblock and turbo from the JDM model because most of the rest of the parts that attach to the longblock must change to work with the USDM 2.0 WRX wiring and ECU.
Intake Manifold and Harness
The rule of thumb here is ECU must match engine and this applies to the manifold and harness as well. The most important reason for these parts to match is because the electronic components change between the models so the USDM ECU would not know what to do with the JDM components like idle air control or the throttle position sensor. The USDM intake manifold is also a great upgrade for its flow and efficiency as well as availability of aftermarket parts. This change will also include the inlet pipe to the turbo along with the BPV and corresponding hose.
Shameless plug moment: We now offer a new plug and play harness for the USDM WRX and V7-9 JDM WRX and STis that will help you sleep a night knowing that your wiring is solid for another 20 years.
Once the manifold and harness changes, it will also sort out the ignition differences. The version 5/6 has an ignition coil and spark plug wires that control the spark for the combustion chamber. Newer WRX’s have what’s called a coil on plug setup. This coil on plug setup is much more efficient than the older style coil with spark plug wires.
Just like the ignition change that will be sorted with the manifold and harness change, so will the fuel injectors and rails. The JDM V5/6 Injectors are side feed injectors which can be very inefficient and problematic when it comes to fueling. In addition it can be difficult to find good replacement injectors and fuel rails and the there aren't many options available for aftermarket/upgraded parts.
The USDM WRX Injectors are top feed which is much more efficient and more commonly used. The upside of running the WRX top feed injectors is that it'll be much easier to find replacement injectors or direct fit upgraded injectors down the road. The same goes with fuel rails and TGV’s.
The JDM version 5/6 has different timing marks on the the camshaft sprocket (under the oil filler neck with the sensor above it) and the crank sprocket (middle behind the crank pulley with sensor above it) that make it so it will not run with the USDM ECU. You will need to use the USDM 2.0 WRX cam sprocket, and the crankshaft sprocket.
JDM models do not come with a water pump with built in port for the oil cooler as well as the oil cooler itself. The oil cooler setup came stock with the USDM WRX and STI that has been proven to help regulate oil and coolant temperatures and it will also bolt right up to the V5/6 Block. With this changes comes the coolant lines and main water channel.
Water Channel and Coolant Lines
With the change in setup for the oil cooler, the associated lines much be changed along with the water channel. You'll see that the JDM water channel exits towards the radiator at angle while the USDM comes straight out.
Turbo Oil Return
Assuming the turbo is being swapped, the feed and return lines are very different between the two engines and must be swapped out but are interchangeable. The coolant channel from the USDM WRX model must be swapped as well.
Header and Uppipe
The header and uppipe (with EGT for emissions compliance) will need to be swapped from the V5/6 for a USDM model (OEM or aftermarket) so that there is a port for the front 02 sensor that does not exist on the JDM V5/6 headers.
Additional notes if this involved an engine swap into a non turbo chassis.
To finish this conversion, you will also need to run the following
USDM WRX power steering pump, reservoir, and lines
USDM WRX Airbox with MAF
USDM WRX Intercooler + BPV
USDM WRX Downpipe
Tuning Note - The JDM turbo, compression, and flow of the heads are all different than a USDM WRX. Although the ECU will likely compensate for most of the this (assuming a TD-04 stock turbo) there are enough changes that it's probably wise to get a tune just to make sure it's running as efficiently as possible.
We borrowed a few screenshots to help our guide from Wide Open Throttle Garage on YouTube. He has a fantastic video that is a good resource as well. Make sure to check it out and give them a like!