What is AVCS?
There are several ways that engineers can improve the performance and efficiency of engines. Camshafts, which determine when intake and exhaust valves open, are typically best suited to certain engine speeds and load conditions. In some cases, it would be better for a valve to open earlier (advance) or later (retard) than the camshaft would normally dictate.
Subaru engineers created a system that allows the camshaft to advance and retard its timing so the valves can be made to open and close at the optimal time for different situations. This system is known as "Active Valve Control System" or AVCS. You can read more about this system and its operation here.
What does this mean for you? If you live in the US and have a 2006+ WRX, a 2004+ Forester XT, 2005+ Legacy GT, or a 2004+ STI, your car's engine already has AVCS. The USDM 2002-2005 WRX and the GC-generation JDM turbo engines did not come with AVCS.
If you have a USDM 2002-2005 WRX and wish to replace the engine with a 2001-2005 JDM EJ205 or EJ207, you will find that these JDM engines came with AVCS. It is possible to use these engines in place of a USDM EJ205 since they are "plug and play" and will run with no modification necessary.
However, they will not perform to their full potential unless the necessary wiring for AVCS is added and the engine control computer is changed for an AVCS-compatible unit. To maximize engine performance and efficiency iWire recommends installing an iWire AVCS Wiring Kit whenever an AVCS-equipped engine is installed in a USDM 2002-2005 WRX. This wiring, coupled with a compatible ECU and a proper tune, will allow the engine to perform optimally in your Subaru.
If you are doing/have done an engine swap with an USDM 2002-2005 WRX into another chassis (like a 2.5RS), the same rules apply. Any vehicle that is wired for a USDM EJ205 can use the 2001-2005 JDM EJ205 and EJ207 longblock, but will require the addition of AVCS wiring and an AVCS-compatible ECU.
What about single vs dual AVCS? Single AVCS changes the valve timing on the intake camshafts only. Dual AVCS changes the valve timing on both the intake and exhaust camshafts. Dual AVCS was introduced on newer engines than are covered in this article, but the principle is the same. Dual AVCS engines are not direct replacements for the USDM EJ205 for several reasons which we will talk about in a future blog post. Only the 2001-2005 JDM EJ205 and EJ207 are drop-in replacements for the USDM EJ205.
How do I know if the JDM engine I purchased has AVCS? An easy way to tell is to look at the timing covers. AVCS-equipped engines have a bulge in the timing cover on the cylinder 1 and 3 head.
My engine was labeled compatible with 2002-2005 USDM WRX. Which engine did I buy?
Good question. Importers are sometimes not up to speed about the differences in Subaru engines. It shouldn't come as a surprise that Craigslist ads and eBay listings sometimes contain inaccuracies. The engines you will typically see listed as "2002-2005 USDM WRX compatible" are as follows.
1999-2000 Version 5/6 Non-AVCS EJ205
This engine requires a complete swap of most of the parts from a USDM 2.0 WRX including the intake manifold, exhaust, cam and crank gears, etc. We will have a detailed blog post describing this process coming in the near future. Since it doesn't have AVCS, simply run it on the USDM 2.0 WRX ECU after the mechanical changes to the engine are completed.
2001-2005 JDM EJ205 w/AVCS
This engine is plug and play except for the addition of the bulkhead AVCS wiring and switching to the matching JDM ECU. The iWire AVCS Wiring kit for this situation would be the AVCS Wiring Kit - Bulkhead Only. This is because the AVCS wiring already exists on the engine and all you'll need to do is get communication from the ECU out to the engine.
2001-2005 JDM EJ207 w/AVCS
Common EJ205 and EJ207 ECU Sticker Labels:
A7 - 1999 and 2000 WRX
F6 - 1999 and 2000 Forester Turbo
J2 - 1999 and 2000 STi ECU
V7 - 2001 WRX
V8 - 2001 STi
4M - 2002 WRX
6L - 2002 STi
5Y - 2003 and 2004 WRX
6A - 2003 and 2004 STi
B1 - 2005 STi (immobilized - do not buy)
F2 - 2005 WRX (immobilized - do not buy)
V2 - 2002 WRX ECU
6G - 2003 WRX ECU
7F - 2004 WRX ECU
6H - 2005 WRX ECU
JDM Forester Drive-by-Wire EJ205 w/AVCS - These engines tend to get listed as Impreza drive- by-wire engines, but in fact they are from 2004+ JDM Foresters.
For these drive-by-wire engines, the complete intake manifold with harness needs to be swapped over from the USDM WRX. This process is very straightforward because the basic setup of these engines is almost identical to the non-drive-by-wire 2001-2005 JDM WRX and STi engines. In order to get the AVCS working with this engine you'll need to track down a non-drive-by-wire 2001-2005 JDM WRX or STi ECU and purchase the iWire Subaru AVCS Wiring Kit for both the bulkhead and the intake so that the AVCS wiring can be added to both the body side and the engine side of the wiring.
We also carry the cable throttle intake manifold harness brand new here if you need it.
If you have more questions about which iWire AVCS WIring Kit to purchase for your application please send us an email to firstname.lastname@example.org or give us a call at 949-510-8278 and we will be happy to assist.