The IAG Stage 4 Extreme Short Block starts with brand new Subaru 2.5L EJ25 engine case halves. The case halves are split and the main webs are CNC machined in our Haas VF-4SS CNC mill for 9.5mm pins to reduce distortion and movement of the case in extreme conditions. The case halves are then reassembled and IAG machines the case to accept the IAG CLOSED Deck Inserts that transform the block into a solid deck. The unique inserts feature small passages that allow needed coolant flow to the deck surface.

The case halves are then CNC machined for our new Fire-Lock head gasket solution that is loosely derived from diesel technology where a counterbore step is machined around each cylinder bore allowing specially sized fire rings to drop into the machined area and head gasket bores. The Stage 4 Extreme case is CNC drilled and tapped to fit 14mm head studs. Utilizing the new Fire-Lock gasket solution along with larger IAG / ARP 14mm head studs, nuts, and washers reduce the chances of the heads lifting under extreme boost conditions. The short block is then Deck Plate bored and honed to 99.75mm in our in-house Sunnen SV-30 the most advanced automotive cylinder hone available. IAG‘s in-house honing process is able to set custom piston to wall clearances to best fit your needs.

The modified case halves are then assembled using a Manley Billet crankshaft that is matched to ACL or King race main bearings. Custom IAG TRI-BEAM +2mm connecting rods by Manley and ARP 625+ rod bolts are utilized along with ACL or King race rod bearings. The case halves are sealed with OEM sealant and ARP main bolts. IAG-Spec 99.75mm Custom Forged Pistons with .250" / .927" wrist pins with electroless nickel plated tops and ring area are chosen to finish the Stage 4 Extreme short block.

IAG‘s custom pistons feature a lightweight design while increasing strength where you need it and are designed to work exclusively with the IAG +2mm Tri-Beam connecting rods. The wrist pin is short and is made from strong H13 tool steel. The pin piers are profiled to increase pin boss strut. Finally, IAG‘s pistons feature a 25% larger oil ring for reduced oil consumption and added gas ports that aid ring sealing in high boost conditions.

Stage 4 Extreme Closed Deck Includes:

• Case Halves - Converted to Closed Deck from brand new OEM Subaru case halves, bored and honed to 99.75mm.
• Pinned Mains - Machine case for 9.5mm pinned mains and lined honed.
• Fire-Lock - IAG Fire-Lock receiver groove machining, latest solution to prevent head gasket failure on high horsepower and high boost Subaru's - *IAG Fire-Lock head gaskets required and sold separately
• Head Studs - Machined for 14mm Head Studs - *Head Studs required and sold separately
• Pistons - IAG-Spec JE FSR 99.75mm 2618 Forged Pistons, Electroless Nickel Plated Tops & Ring area, Ring Set, .250" / .927" H13 Wrist Pins, Clips, (Perfect Skirt Coating and Offset Wrist Pins)
• Connecting Rods - IAG-Spec Tri-Beam Connecting Rods with ARP 625+ Rod Bolts.
• Rod / Main Bearings - ACL or King Race Bearings.
• Crank - Manley Billet Turbo Tuff Crankshaft.
• Case / Main Bolts - ARP Main Bolts.

Power:

• The IAG Stage 4 Extreme Short Block has a power output rating of 1100BHP.

Compression Ratio:

• 8.5:1 on D Cylinder Heads (EJ255)
• 8.2:1 on B, V and W EJ257 Heads with standard thickness gasket.

Head Gasket Required:

• IAG Fire-Lock .051" Head Gaskets with IAG-Spec Alloy Ring Set - PN# IAG-ENG-1740

Additional Options Available:

• Head Studs - IAG / ARP Spec 14mm head studs, nuts, and washers required (Sold Separately)
• Oil Pump - Subaru JDM 12mm High Volume Oil Pump or 11mm Subaru Oil Pump (Sold Separately)
• Head Gaskets - IAG Fire-Lock .051" Head Gaskets with IAG-Spec Alloy Ring Set - Required for use with this short block (Sold Separately)
• Hardware/Seals - OEM cover and seal kit (Sold Separately)

Not planning on reusing your original short block service plugs and covers? IAG offers a simple comprehensive cover and seal kit that includes:

• (1) Rear main seal
• (3) OEM wrist pin plugs
• (3) OEM wrist pin plug washers
• (1) OEM separator cover
• (6) OEM separator cover bolts
• (1) OEM wrist pin service cover
• (1) OEM wrist pin service cover O-ring
• (2) OEM wrist pin service cover screws.

If you are reusing your original wrist pin service plugs and covers always replace the following components before installing a short block to avoid potential leaks:

• (3) OEM wrist pin plug washers
• (1) wrist pin service cover O-ring

Never reuse a rear main seal on a new short block.

Note: All IAG Short Blocks are balanced and blueprinted.

Please review the PDF document below regarding installation, break-in procedures and warranty information.