IAG Stage 4 Extreme EJ25 Subaru Closed Deck Short Block For WRX, STI, LGT, FXT

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

Online ordering is currently disabled, but please call the shop for pricing and orders! 250-300-4959

SKU: IAG-ENG-1453 Categories: ,


IAG Stage 4 Extreme Closed Deck EJ25 Subaru Short Block

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 IAG Billet crankshaft by Callies 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
  • Head Studs –Machined for 14mm Head Studs.
  • 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 –Billet Crank by Callies
  • Case / Main Bolts –ARP Main Bolts.
    • *IAG Fire-Lock .051″ Head Gaskets with IAG-Spec Alloy Ring Set* PN# IAG-ENG-1740Additional Options Available:
      • Head Studs –IAG / ARP Spec 14mm head studs, nuts, and washers
      • Head Gaskets –IAG Fire-Lock .051″ Head Gaskets with IAG-Spec Alloy Ring Set* Required for use with this short block
      • Oil Pump –IAG Stage 2 CNC Ported 11mm EJ Oil Pump or Subaru JDM 12mm High Volume Oil Pump
      • IAG Oil Pickup – Upgraded oil pickup featuring heavy gauge steel tubing, 2 point bracket & mesh filter
      • IAG Oil Baffle – Upgraded oil control baffle and windage tray
      • IAG Oil Pickup & Baffle Set – Upgraded oil pickup, oil control baffle, and windage tray
      • Hardware / Seal Option –(Includes: Wrist pin plugs, washers, separator cover, bolts, etc. In case you don’t want to transfer from the original engine).

      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:

    *All IAG short blocks are balanced and blueprinted.

Additional information

Weight 133 lbs
Dimensions 19.7 × 19.7 × 17.7 in


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