EJ255 vs EJ257 Short Block Guide

The badge does not make this call. Model year, cylinder heads, compression, and a realistic power goal do. Pick by badge alone and you can end up with the wrong compression and the wrong heads on an otherwise sound build.

What actually differs

Both blocks come from the same turbocharged 2.5-liter EJ family. They share the basic layout: case, crankshaft, connecting rods, pistons. That shared layout does not make them interchangeable.

In the US market, the EJ257 name belongs to the STI. Every other turbocharged 2.5-liter EJ application — WRX, Forester XT, Legacy GT — carries the EJ255 name. That split narrows the search. It is not a fitment check. Subaru changed specifications across models and years.

The differences that matter:

• Pistons and heads set compression. Piston dish and head chamber shape work together. Two blocks with the same displacement can produce different compression ratios under different heads.
• Deck configuration. Deck style is how much support surrounds the tops of the cylinder bores. WRX applications typically run an open deck. STI applications typically run a semi-closed deck. Treat that as an application pattern, not a promise based on the name alone.
• The parts around the block. Heads, oil system parts, sensors, turbo, and engine management differ by application and year. The short block has to work with all of them.

	EJ255	EJ257
US application	WRX, Forester XT, Legacy GT	STI
Deck	Typically open deck	Typically semi-closed deck
Compression	Set by pistons and heads	Set by pistons and STI specification
Before ordering	Confirm year and heads	Confirm year and heads

Which one fits your car

Start with what the car actually is, then verify what is in it now.

An STI build starts with the EJ257. A WRX, Forester XT, or Legacy GT build usually starts with the EJ255. Neither starting point is a guarantee. Previous owners swap parts. A used car's current setup can differ from its factory build sheet.

Record the VIN, model year, original engine code, and head casting before you order anything. Confirm the parts already on the car. A short block that bolts in can still create the wrong compression or the wrong tuning requirements.

An EJ257 is not an automatic upgrade for an EJ255 car. The intended vehicle controls which heads, oil parts, sensors, and tune have to work together. A matched build beats a stronger-sounding badge.

For the EJ255 on its own — specs, reliability, and power — see the EJ255 engine guide. If the EJ257 is your likely match, Crawford's EJ257 short block buyer guide goes deeper on that block. If the build grows into a complete engine, the EJ257 long block guide covers that route.

OEM or built

OEM for a stock-style build. A brand-new OEM block is the direct choice for a dependable replacement or a mild street build. The OEM EJ255 short block suits most WRX, Forester XT, and Legacy GT replacement plans. The OEM EJ257 short block is the matching starting point for STI applications. Verify the model year and every mating part before ordering either one.

Built for higher load. Higher boost, a bigger turbo, or sustained track use puts more load on the block than a stock-style plan allows. That is where a built short block earns its cost. Crawford built short blocks are blueprinted EJ257 builds for upgraded STI applications. Stronger internals give the tuner a better foundation. They do not replace the tune or the supporting parts.

Both engines share the same known weaknesses: rod bearings and ringlands. No short block, OEM or built, protects an engine from a poor tune, weak fuel delivery, excess heat, or missed maintenance. A conservative OEM build can outlast a built engine running the wrong calibration. Reliability comes from the whole system — air, fuel, spark, oil, and temperature — matched to how the car is used.

Forged internals, honestly

Forged pistons and rods add margin when planned power and heat exceed what an OEM-style build should carry. That is all they do. They do not correct poor machining, weak oil control, excess heat, or a bad tune.

The margin only survives if the machine work is right: correct bearing clearances, correct ring gaps, careful fastener work. A forged parts list is the starting point, not the build. Define the car's use first — daily driver, track car, rally car — then match compression, boost, fuel, and tuning as one system.

Before you order

Settle these before any block ships:

1. Identify the car. VIN, model year, trim, transmission, original engine code, head casting, and any prior engine or head work.
2. Calculate the finished compression. Your builder should run the number with your exact heads and gasket thickness. Confirm piston-to-valve clearance if the heads run larger cams or altered valve timing.
3. List the full setup. Turbo, injectors, fuel pump, intake, exhaust, boost target, fuel type, and the car's main use. Plan a startup map and a final tune for the finished engine. Do not drive under boost on a calibration built for a different compression ratio, turbo, or fuel.
4. Inspect the supporting parts. Oil pump, pickup, pan, and cooler. Water pump, thermostat, and radiator. Replace questionable parts instead of moving an old problem onto a fresh block. Confirm every gasket and seal by application, not by appearance.
5. Set a realistic power target. State how the car will be used, not just a peak number. A daily-driven Legacy GT and a track STI need different builds on the same basic engine.

Break-in and warranty

Break-in is part of the build, not an afterthought. Oil changes at 500 and 1,500 miles. Keep engine speed between 2,000 and 4,500 RPM and vary it — no sustained cruising, no full-throttle pulls. Do not exceed 80% of target boost until break-in is complete. The first oil analysis is mandatory.

Crawford's built engines carry a 1-year / 12,000-mile warranty, and the break-in and first oil analysis are conditions of it. Keep every invoice and service record. Crawford's Subaru engine short blocks are built from brand-new OEM blocks — no core required or needed — and every build is specified around the vehicle and its goals.

Frequently asked questions

What is the primary difference between the EJ255 and EJ257 short blocks? They share the same basic 2.5-liter EJ architecture. The complete specification differs by application and model year. In the US, EJ257 means STI; EJ255 covers the other turbocharged 2.5 applications. Piston design, cylinder heads, compression, and supporting parts still have to be checked on the individual car.

Is the EJ257 better than the EJ255? Not automatically. The EJ257 is the direct choice for an STI or a build planned around STI specifications. An EJ255 is often the better match for a WRX, Forester XT, or Legacy GT that needs correct compression and factory-style compatibility. The vehicle, heads, use, tune, and power goal make the call.

How much horsepower can a stock EJ255 handle? There is no single dependable number. Safe output depends on engine condition, fuel quality, boost, torque delivery, cooling, oil control, and calibration. A healthy block on a conservative tune can outlast a poorly tuned engine making less power. Set the target with your builder and tuner after the existing engine and supporting systems are inspected.

How much horsepower can a stock EJ257 handle? Same answer. There is no guaranteed ceiling. Age, maintenance history, fuel, tuning, torque curve, heat, and use all move the limit. Do not confuse a stock block with a built one — built EJ257 configurations exist for owners whose goals exceed stock specifications.

Are the EJ255 and EJ257 short blocks interchangeable? Sometimes, in some builds. They are not universal drop-in replacements. Model year, heads, piston design, compression, oiling details, sensors, and supporting hardware decide it. A mismatch can change compression or create installation and tuning problems. Confirm the exact part number and the complete engine combination before ordering.

Start with the car

A block decision made without the model year, the supporting parts, and the power target leads to rework and a stalled build. Compare Crawford Performance Subaru engine short blocks, then contact Crawford Performance at (855) 677-8243 with your model year and power goal to narrow the choice.