IAG Performance / Crest CNC Stage X 2.5L Subaru Billet Aluminum Short Block For WRX, STI, LGT, FXT

Part Details:

The IAG Performance CREST CNC Stage X (Stage 4 Extreme) Short Block is an ultra-high-end engine foundation built for Subaru EJ25 applications requiring maximum strength, stability, and race-level reliability. Rated for builds targeting up to 1100 BHP, this short block is engineered for extreme boost, sustained high RPM, and competitive motorsport environments where conventional EJ architectures are no longer sufficient.

This short block is designed for serious drag racing, high-horsepower street builds, and track-focused applications that demand absolute confidence in the engine’s bottom end.

CNC Machining & Closed Deck Conversion

Each Stage X short block begins with brand-new Subaru EJ25 case halves that are CNC-machined in-house by IAG. The main webs are machined for 9.5mm pinned mains to reduce case distortion and movement under extreme loads. The case halves are then converted to a solid closed-deck configuration using IAG’s proprietary closed-deck inserts.

These inserts are designed with integrated coolant passages, allowing necessary coolant flow to the deck surface while dramatically improving cylinder wall support under high boost.

Fire-Lock Sealing & Head Stud Preparation

To address head gasket sealing at extreme cylinder pressures, the Stage X case is CNC-machined for IAG’s Fire-Lock head gasket system. This technology uses receiver grooves machined around each cylinder bore to accept precision fire rings, improving combustion sealing under high boost.

The block is also CNC drilled and tapped for 14mm head studs. When combined with IAG Fire-Lock head gaskets and 14mm ARP hardware, this setup significantly reduces the risk of head lift in extreme boost applications.

Precision Boring, Honing & Blueprinting

After machining, the block is deck-plate bored and honed to 99.75mm using IAG’s in-house Sunnen SV-30 honing equipment. This process allows IAG to set custom piston-to-wall clearances based on the intended application, ensuring optimal performance and longevity.

All Stage X short blocks are fully balanced and blueprinted to maintain precise tolerances, consistent oil clearances, and repeatable performance at extreme power levels.

Engine Internals & Rotating Assembly

Internally, the Stage X short block is assembled using premium race-grade components selected for maximum durability. The rotating assembly features a billet crankshaft by Callies, paired with ACL or King race main bearings and secured with ARP main bolts.

Custom IAG-spec +2mm Tri-Beam connecting rods by Manley with ARP 625+ rod bolts are used alongside ACL or King race rod bearings. The piston assembly consists of IAG-spec 99.75mm forged pistons with electroless nickel-plated crowns and ring lands, designed exclusively for use with the +2mm Tri-Beam rods.

The pistons utilize short H13 tool steel wrist pins, reinforced pin bosses, a 25% larger oil ring for reduced oil consumption, and gas ports to improve ring sealing under high boost.

Reliability & Performance Benefits

At extreme horsepower levels, EJ engines commonly fail due to case movement, head gasket failure, or rotating assembly limitations. The Stage X short block addresses these issues through closed-deck reinforcement, pinned mains, Fire-Lock sealing technology, and a fully billet rotating assembly.

This configuration is intended for builders who require maximum reliability in extreme boost, E85, and motorsport environments where engine failure is not an option.

Vehicle Fitment Overview

This short block is compatible with turbocharged Subaru EJ25 platforms, including WRX, WRX STI, Legacy GT, and Forester XT models. Full year-by-year compatibility is listed in the Vehicle Fitment tab above.

This is a race-focused performance short block and is not intended as a stock replacement. Vehicle configuration, cylinder head selection, and overall build strategy should always be verified prior to purchase.

What’s Included

• Brand-new Subaru OEM EJ25 case halves converted to closed deck, bored and honed to 99.75mm
• Machined for 9.5mm pinned mains and line-honed
• IAG Fire-Lock receiver groove machining (Fire-Lock head gaskets required)
• Machined for 14mm head studs
• IAG-spec 99.75mm forged pistons with electroless nickel-plated crowns and ring lands
• 0.250″ / 0.927″ H13 tool steel wrist pins with skirt coating
• IAG-spec +2mm Tri-Beam connecting rods by Manley with ARP 625+ rod bolts
• ACL or King race rod and main bearings
• Billet crankshaft by Callies
• ARP main bolts

Compression Ratio

• 8.5:1 – EJ255 (D heads)
• 8.2:1 – EJ257 (B, V, W heads) with standard thickness head gasket

Required Components

• IAG Fire-Lock 0.051″ head gaskets with IAG-spec alloy ring set (PN: IAG-ENG-1740)

Optional Add-Ons

• IAG / ARP 14mm head stud kit
• IAG Fire-Lock head gasket set
• Subaru JDM 12mm or 11mm oil pump
• IAG upgraded oil pickup
• IAG oil baffle and windage tray
• IAG oil pickup & baffle kit
• Hardware and seal kit

Installation & Build Notes

• Professional installation is mandatory
• ECU tuning is required
• Comprehensive supporting modifications (fuel system, turbo system, cooling, oiling) are essential
• This short block is designed for extreme power and competition use
• Final power capability depends on the complete engine build and tuning strategy

Recommended Supporting Upgrades

• Air / Oil Separator and Oil Catch Cans – Critical for managing crankcase pressure and oil vapor in high boost competition builds.
• Advanced Oiling Upgrades – Reinforce lubrication system reliability under sustained high RPM and track conditions.
• Head Gaskets & Sealing Components – Required for proper combustion sealing at extreme cylinder pressures.
• High-Strength Hardware & Fasteners – Supporting hardware essential for billet engine builds.

Note: Designed for advanced builds requiring professional assembly, custom tuning, and comprehensive supporting modifications.

Learn more about IAG Performance engine and reliability solutions