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IAG Stage 4 Plus EJ25 Subaru Closed Deck Short Block (WRX, STI, LGT, FXT)


  • $ 4,899.99
  • Save $ 24500

The IAG Stage 4 Plus Short Block starts with brand new Subaru 2.5L engine case halves. IAG machines the case halves assembled together in their Haas VF-4SS CNC mill 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. Next the short block is Deck Plate bored and honed to 99.75mm. 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 new 2012+ Subaru 2.5L heat-treated STI crankshaft that is matched to ACL or King race main bearings. Manley I-Beam and ARP2000 rod bolts are utilized along with ACL or King race rod bearings. The case halves are sealed with new OEM main/case bolts and sealant (upgrading to ARP mains requires line honing). IAG Spec 99.75mm Custom Forged Pistons by Manley are chosen to finish the Stage 4 short block. IAG‘s custom pistons feature a lightweight design while increasing strength where you need it, and are designed to work Manley I-Beam connecting rods. The wrist pin is short and is made from strong tool steel. The pin piers are profiled to increase pin boss strut. 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 Closed Deck Includes:

  • Case Halves - Converted to Closed Deck using brand new Subaru OEM case halves, bored and honed to 99.75mm.
  • Head Studs - Machine case to fit 1/2 inch head studs - *Head studs sold separately
  • Pistons - IAG Custom Spec 99.75mm 2618 Forged Pistons with .170 inch wall tool steel wrist pins by Manley Performance
  • Connecting Rods - Manley I-Beam w/ ARP2000 Rod Bolts.
  • Rod / Main Bearings - ACL or King Race bearings.
  • Crankshaft - Standard New Subaru Heat-Treated 2012+ STI Crankshaft.
  • Case / Main Bolts – Standard FHI Subaru case bolts.

Additional Options Available:

  • Crank - Manley Billet Turbo Tuff Crankshaft - $1300
  • Line Hone - For use with ARP Case Bolts - $250
  • ARP Case Bolts - (Requires line honing) - $400
  • Pinned Mains - Machine case 9.5mm pinned mains (Includes line boring service) - $350
  • O-Ringing - Machine and O-Ring deck surface - $200
  • Oil Pump - ACL Orbit High Volume Oil Pump - $249, or Subaru 11mm Oil Pump - $189.95
  • Wrist Pins - Extreme .210 inch 9310 thick-wall wrist pins - $100
  • Rod Bolts - 625+ ARP rod bolts - $200
  • Head Gaskets - JE Pro Seal .039 inch Head Gaskets - $96 or Cosworth 1.1mm Head Gasket - $158
  • Head Studs - IAG 1/2 inch ARP Head Stud Set - $499.99
  • Hardware / Seal Option - $99.99 (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 Recommendations:

  • *IAG Recommends JE Pro Seal .039 inch head gaskets for B and D casting cylinder heads.
  • *IAG Recommends Cosworth 1.1mm head gaskets for all V and W casting cylinder heads.

The IAG stage 4 Short Block has power output rating of 900BHP.

*All IAG short blocks are balanced and blueprinted.

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