IAG Performance 550 Series EJ25 Long Block w/ IAG 550 Heads 2002-2014 WRX / 2004-2021 STI / 2004-2013 Forester XT / 2005-2009 Legacy GT

The IAG 550 Long Block is a complete, valve cover-to-valve cover crate engine designed for Subaru enthusiasts seeking a “drop-in” performance upgrade. Ideal for WRX, STI, Forester XT, or Legacy GT applications, this package combines race-proven short block and cylinder head components to deliver reliable performance up to 550 BHP.

Performance Benefits

• Increased durability and strength for high-boost, high-performance EJ25 engines.
• Optimized piston and rod design for reduced reciprocating mass.
• Ready to support upgraded turbos and high horsepower applications.

Package Overview

• IAG 550 Short Block: Forged pistons, H-beam connecting rods, nitride-treated OEM STI crankshaft, and race-grade bearings.
• IAG 550 Cylinder Head Package: Subaru OEM castings, GSC valvetrain components, and GSC S1 Billet camshafts.
• Additional Components: ARP 2000 11mm head studs and all necessary gaskets for a complete valve cover-to-valve cover assembly.

IAG 550 Short Block Highlights

• Built from brand new EJ25 2.5L Subaru engine case halves, precisely measured and assembled.
• IAG Spec JE 99.75mm forged pistons (2618 T6 alloy) with asymmetrical skirts for reduced weight and improved flame travel.
• IAG Spec H-beam forged connecting rods with ARP 2000 rod bolts for maximum strength.
• OEM 2017+ STI nitride-treated crankshaft matched to ACL or King race main bearings.
• Sealed with new OEM main case bolts and sealant.
• Designed to support higher cylinder pressures from larger turbochargers or increased boost.

IAG 550 Cylinder Head Package

• Components include:
  • GSC standard-size intake (36mm) and exhaust (32mm) valves
  • GSC Viton valve stem seals
  • IAG Stage 1 valve springs with titanium retainers
  • OEM valve keepers
• GSC Power-Division S1 camshafts for increased power and torque across the RPM range.
• Precision-machined in-house:
  • Centroid 5-axis CNC cam clearance machining
  • Multi-angle valve job on intake/exhaust seats
  • Deck resurfaced for smooth, even finish
• Ultrasonically cleaned and reassembled with high-quality components.

IAG Engine Installation Documentation

Full Component Breakdown: 

• Case Halves -Brand new Subaru OEM case halves 99.75mm Stock Bore
• Pistons -IAG-Spec JE 99.75mm Forged Pistons, Ring Set, .180" Chromoly Steel Pins, Clips, (Perfect Skirt Coating and Offset Wrist Pin)
• Connecting Rods -IAG Spec H-Beam Rods w/ ARP2000 Rod Bolts
• Rod / Main Bearings -ACL or King Bearings
• Crankshaft -Standard New Subaru Nitride Treated 2017+ STI Crankshaft
• Case / Main Bolts -Standard FHI Subaru case bolts

IAG 550 Cylinder Heads:

• Heads - Brand New Subaru OEM WRX STI Cylinder Head Castings
• Intake Valves - GSC 36mm (Standard) Intake Valves
• Exhaust Valves - GSC 32mm (Standard) Exhaust Valves
• Springs / Retainers - GSC Valve Springs & Titanium Retainers
• Guides - OEM Valve Guides
• Valve Seals - GSC Valve Stem Seals
• Lifters - OEM Lifter Buckets
• Camshafts - GSC Stage 1 Billet Camshafts
• Multi-Angle Valve Job
• Machined Cam Lobe Clearance
• Resurface
• Ultrasonic Cleaning
• Final Lash

Gaskets, Hardware & Accessories:

• Head Studs - ARP 2000 11mm Set
• Head Gaskets - OEM
• Valve Cover Gaskets - OEM
• Cam Seals - OEM
• Valve Covers - OEM
• Wrist Pin Seal, Rear Main Seal & Separator Kit
• Crankshaft Woodruff Key