EJ20 and EJ25 rebuild kits: what NZ Subaru builds need

Subaru builds in New Zealand usually start after one of two phone calls. Either a ringland has let go on an EJ25 after a tune that was optimistic about our fuel, or a rod bearing has gone quiet then loud on an EJ20 that saw track work. Both are fixable, and both are the point at which people decide to build the engine properly instead of putting it back to standard.

This guide covers what an EJ20 or EJ25 rebuild kit contains, why our packages are split by thrust type and AVCS, and which supporting parts matter on a boxer. One thing worth saying at the top: we sell the parts and the packages, not complete or crate engines.

The short answer

• A refresh kit is bearings, gaskets, seals and plugs. That is enough for a healthy engine coming apart for a head gasket or a service.
• A forged package is CP pistons, Manley or Eagle rods, stud kits, a metal head gasket and ACL Race Series bearings. Our EJ20 packages sit here.
• Before you order anything, find out whether your block is centre thrust or end thrust, and whether the engine has AVCS. Both change the parts.
• Do the oil pump and the seals while it is apart. Boxers are not fun to strip twice.

What is in a rebuild package

The standard package contents are on our Engine Rebuild Packages page: forged pistons, forged rods, a Cometic MLS or Tomei head gasket, an ARP or Mazworx head stud kit, a main stud kit where the engine takes one, and ACL Race Series main and rod bearings. Every package is priced under the total of the individual parts.

Where the EJ20 packages differ from our other engines is what the titles call out. Instead of gasket thickness, an EJ20 package title tells you the rod brand and the thrust type, and whether it is the AVCS build.

The standard non AVCS options are the CP piston and Eagle rod package for an end thrust block, the same build in centre thrust, and CP pistons with Manley rods in centre thrust or end thrust.

The AVCS engines get four matching listings, including the CP piston and Manley rod AVCS package for an end thrust block and a CP and Eagle rod version in both thrust layouts. Pick the line that matches your block and your heads, not the one that is cheapest that week.

Centre thrust, end thrust and AVCS

This is the part that catches people out, so it gets its own section rather than a footnote.

Subaru used more than one main bearing layout across the EJ family. ACL list a Race Series main centre thrust set as 5M8297H and a main end thrust set as 5M8309H, and there is a further end thrust part number in the range. Order the wrong one and the rebuild stops on the bench while a bearing set flies around the country.

The same logic applies to AVCS. Our packages are split into AVCS and non AVCS, and so is the Kelford camshaft range, where the EJ20 WRX STI with AVCS collection covers version 6 onwards engines. If you have bought an EJ207 short block or a long block with no history, confirm what you actually have before you order parts against a guess. Ten minutes with the engine and a torch saves a fortnight.

Choosing pistons, rods and compression

Our EJ20 packages run CP pistons. If you are building outside a package, Manley Subaru pistons list a wide range for the EJ205 and EJ257 in standard and oversize bores, including stroker sets, with the compression ratio and bore stated in every title. That matters on a Subaru, because the bore you finish at depends on what the machinist finds.

Rods follow the pattern we use across the range. Manley rods go into the higher rpm and higher power builds, and Manley also list Turbo Tuff I Beam rods for the EJ20 and EJ25, plus a longer version for the EJ205 and EJ257. Eagle rods are the value option in the packages and are plenty for a strong street car.

Rod bearings deserve a look before you order. ACL list the EJ20 and EJ25 rod bearing set at 52mm, and journal sizes are not identical across every EJ, so measure rather than assume. On a boxer, oil supply and bearing clearance decide how long the bottom end lasts far more than the rod brand does.

Head studs, gaskets, bearings and the small stuff

ARP 260-4701 is the head stud kit for the 2.0L and 2.5L DOHC EJ, and it is the part we would fit before adding boost to a standard engine. The rest of the range sits in ARP head studs, and ARP also list a WRX wheel stud kit if you are tidying up the rest of the car.

Cometic list an EJ20 head gasket at 1.0mm thick in 93.5mm, plus EJ20 and EJ25 exhaust gaskets. The wider MLS range is under Cometic head gaskets. As always, order the bore that matches your machining.

Spark plugs are split by age of engine: NGK BKR6EIX iridium plugs come as a set of four covering the EJ20, and NGK ILFR6B covers the late EJ20 and EJ25. GSC make a Viton stem seal set for the EJ series, and there is a K&N oil filter listed for the family.

The oil pump is the one people leave until last and regret. We list the IAG Stage 2 CNC ported EJ25 11mm oil pump, which covers a long span of WRX, STI, Legacy GT and Forester XT model years. If you are not upgrading it, at least replace the seals and check the pump properly while the engine is on the bench.

Head parts are where an EJ build gets expensive quickly, so it is worth being deliberate. Kelford list single springs with titanium retainers for the WRX, a spring and titanium retainer set for the EJ20 and EJ25, DLC buckets in a range of thicknesses for shimming, valve guides and a Ferrea oversize intake valve. Supertech Subaru exhaust valves cover Inconel and black nitrided stainless in standard and oversize for the EJ20 and EJ25. Our Kelford cam selection guide is the place to start on profiles.

Build it your way

If your build does not match a package, use the Engine Builder. Choose the engine, then step through pistons, rods, bearings, gaskets and studs while it holds the combination together. It suits a stroker EJ, a hybrid build, or a low compression EJ20 aimed at one particular turbo.

The full parts catalogues are EJ20 and EJ25, and the EJ25 hub page gives the overview of that side of the family.

Where NZ Performance fits

We have been selling performance parts out of Palmerston North since 2003, and the people answering the phone build and race their own cars. EJ hardware is held in New Zealand where we can, so an ARP stud kit or an ACL bearing set usually ships the same or next working day rather than sitting on an overseas order.

Searches like "ej20 engine for sale nz" land on us constantly, so here it is plainly: we sell parts and rebuild packages, not complete engines. Rebuilding your own block or a used import short block costs less than a mystery engine and you end up knowing exactly what is inside it. The full comparison is in rebuild versus import, and if boost is the goal, head studs, gaskets and pistons for big boost is worth ten minutes. Building a four cylinder Mitsubishi instead? The 4G63 rebuild kit guide follows the same shape.

FAQ

What is in an EJ20 rebuild kit?

Our EJ20 packages contain forged pistons, forged rods, a Cometic MLS or Tomei head gasket, ARP or Mazworx stud kits and ACL Race Series main and rod bearings. Each title names the piston brand, the rod brand, whether it is built for a centre thrust or end thrust block and whether it suits an AVCS engine. Oil pumps, cams, springs and valves are ordered separately.

Centre thrust or end thrust, and how do I tell?

Subaru used both layouts, and the main bearing set differs for each. ACL list a centre thrust set as 5M8297H and an end thrust set as 5M8309H, and our packages are split the same way. Get your engine builder to confirm which block is on the stand before you order, because the wrong set stops the job.

Do I need the AVCS version of the package?

Only if the engine has AVCS. We list AVCS and non AVCS EJ20 packages side by side, and the Kelford cam range is split the same way for version 6 onwards STI engines. If you bought an EJ207 or an STI short block with no paperwork, check the heads first.

Can I buy a complete EJ20 engine from NZ Performance?

No. We sell rebuild parts, packages and the Engine Builder, not complete or crate engines. Most people searching for an EJ20 for sale end up rebuilding their own block or a used import short block, which costs less and gives you a known spec.

Is the oil pump worth upgrading on an EJ25?

It is worth attention while the engine is apart, because you do not want to strip a boxer twice. We list the IAG Stage 2 CNC ported EJ25 11mm oil pump covering a wide span of WRX, STI, Legacy GT and Forester XT years. At the very least, replace the seals and inspect the pump before reassembly.