Buying a JDM Engine? Here are the differences between the EJ20G, EJ20K, and EJ205.

Buying a JDM Engine? Here are the differences between the EJ20G, EJ20K, and EJ205.

Apr 15, '21

If you are looking for information about the newer JDM Engines, 2001+ please check out this POST


NOTE: As of January 2021 we are longer wiring Version 1 through 6 engine swaps. Customers have had problems not only getting the swap going but also keeping them running due to harness condition issues/availability as well as the lack of replacement parts, tuning options, and not passing smog. We highly suggest if you are looking for a swap engine to check out these options.

If you have a V5/6 we can wire it up if you convert it to match an 02-05 WRX. More information about this process can be found if you click here.


Long before the WRX was introduced to the United States for the 2002 model year, the Japanese were enjoying turbo boxer power in their Imprezas. These old Japanese Domestic Market (JDM) Subarus are now several decades old, and many have been retired from the road with less than 100,000 km on the odometer. Because of this, there is a large supply of inexpensive JDM engines available from importers on Ebay and Craigslist. JDM engines are a popular choice for those looking to give their Subaru more power on a reasonable budget.


Here at iWire, we often get questions from customers who are looking to swap their stock Subaru engine for a JDM turbo engine. While Japanese-market motors are often less expensive than equivalent US-market motors, there are things to consider before purchasing a JDM motor.


In this guide we will focus on the engines found in the first-generation Impreza WRX and STI, commonly known as the “GC” generation. In the six versions of the GC Impreza WRX/STI, Subaru used three different turbocharged engines. Here's how to identify each motor, and the pros and cons of using it in your swap:

1992-1996 Version 1 and 2: The first WRX and STI models used the EJ20G. The EJ20G is considered to be a good engine, but it is old. Most of the plastics will be deteriorating, the wiring will probably be stiff and brittle, and there will be no way to pass this engine through emissions testing. Tuning options for these engines are limited, and replacement parts are difficult to find.


Subaru Impreza WRX STI EJ20G


Identifying marks: 90 degree bend at the turbocharger inlet. Coil-on-plug ignition system. Ridges and the words “4CAM 16VALVE” cast into valve covers. “Slanty” air-air intercooler on Impreza models, air-water intercooler on Legacy models. You can tell the difference between V1 and V2 with the connector on the underside of the throttle body. V1 uses 3 smaller plugs for camshaft position, crankshaft position, and the knock sensor while V2 combines these into a single 12 pin connector.


Essential accessories: Sensor group that is located on the strut tower bracket (passenger side for left hand drive countries); mass airflow sensor with housing.

1997-1998 Version 3 and 4: These vehicles used the EJ20K motor. Despite an excellent-flowing head design, these engines are known for bottom end bearing problems. As with all JDM motors, the ECU tune is designed around running a higher-octane fuel than is available in the United States. The EJ20K can make excellent power when the shortblock is rebuilt and the heads are paired with a standalone engine management system.


NOTE: Oddly, first-generation turbocharged Foresters are listed by Subaru as having the EJ20G engine, but in reality they are equipped with the EJ20K. The correct replacement parts for the “EJ20G Forester” are easily found by looking for EJ20K Impreza parts.


Subaru Impreza WRX STI EJ20K

Identifying marks: Hard line for idle air control valve running on top of engine. Turbocharger inlet runs under intake manifold. Coil pack centered on intake manifold. Smooth valve covers.

Essential accessories: Sensor group that is located on the strut tower bracket (passenger side for left hand drive countries); mass airflow sensor with housing.

1999-2000 Version 5 and 6: The most modern engine offered in the GC Impreza WRX and STI was the first iteration of the EJ205 and EJ207 found in the version 5 and 6 WRX and STI, respectively. This motor is a competent performer, but has significant differences from the EJ205 found in the USDM 2002-2005 WRX. Engine management from the factory has a very primitive form of OBDII that is not compatible with most scanning software available in the United States, and the ECU can only be reflashed with ECUTEK software.


Subaru Impreza WRX STI EJ205 EJ207


Identifying marks: Looks similar to EJ20K, but coil pack is offset from center on intake manifold. No hard line for idle air control valve on top.


Essential accessories: Sensor group that islocated on the strut tower bracket (passenger side for left hand drive countries) (although for the V5/6, USDM equivalents exist); mass airflow sensor with housing.


WARNING: Many JDM importers have sold these engines to customers claiming that they are a drop-in replacement for a USDM EJ205. This is not the case. These engines can be used in place of a USDM EJ205, but this requires extensive modification. If a “2001-2005 JDM WRX engine” is labeled as “NON AVCS” it is actually a V5/6, as seen in the listing below:


V5/6 EJ205

Tuning JDM engines:

For customers that do not require OBDII for emissions, there are tuning options for JDM motors:

  • ECUTEK - a reflash similar to a Cobb or open source tune (Version 5 and 6)

  • Enduring Solutions - a chip that can be soldered to the ECU board and then reprogrammed with their proprietary software only (Version 1 thru 4)

  • Haltech - standalone engine management that is plug and play with Haltech’s adapter harness (Version 1 thru 6)

  • Apex’i PowerFC - standalone engine management that is plug-n-play (Version 1 thru 6)

  • RobTune - the RobTune chip is available for EJ20G ECUs and is designed for engines running either 440cc or 550cc injectors with a TD05 turbocharger, with a few options for fine-tuning (Version 1 and 2)


The EJ20G and EJ20K are two decades old at the time of writing, and it is difficult to find them in good shape. Even in the best condition these motors will need serious inspection and reconditioning of wiring, sensors, and vacuum lines. The end result will be a motor with around 220-250hp and few options for tuning to improve that number. Passing emissions with either of these engines is for practical purposes impossible.


The Version 5 and 6 EJ205 and EJ207 is a good motor, but it is over 15 years old now. It is considered reliable and will make around 250hp. Unfortunately, users have few tuning options on the stock ECU. Again, it will be difficult to pass emissions with one of these engines, due to the OBDII port that isn’t compatible with typical scan tools. The Version 5 and 6 longblocks can be converted to work with the wiring and ECU found in the 2002-2005 USDM WRX. This conversion requires some work, but allows for a much wider range of tuning options as well as the ability to pass emissions testing.


JDM engines may look attractive for their low prices and low mileage, but they aren’t as inexpensive as they seem due the parts that are likely to be missing. Below is a cost breakdown of parts for a typical EJ20K conversion:


Breakdown of costs:

Engine: $1149

Wiring harness: $600

ECU: $200

Turbo engine crossmember: $200

Engine management (optional but recommended): $1614

Harness Merge: $630

Total: $4193 with Haltech Elite, $2779 with OEM ECU


Engine: $1149




Wiring harness: $600



ECU: $200



Sensor Group on Strut Tower Bracket: Price varies, these are very difficult to find.

Strut Tower Sensor Group JDM WRX EJ20G EJ20K


Turbo engine crossmember: $200



Engine management (optional but recommended for older JDM motors): $1614

Note - Vipec also makes a PnP ECU for these setups



Harness Merge: $630



iWire’s recommendation:

Customers who plan to swap their vehicle use either the EJ205 from the USDM 02-05 WRX, the EJ207 from the JDM Version 7 and 8 STI, the EJ255 from the USDM 06-07 WRX and 04-08 Forester XT, or the EJ257 from the USDM 04-07 STI. These engines are newer, more reliable, and more powerful than older JDM engines. They also offer advanced tuning options with the stock ECU, and they can pass emissions testing in all 50 states.


#JDM #EJ20 #EJ205 #EJ207 #EngineGuide #AVCS