IAG Stage 4 Plus Closed Deck Short Block 2.5L Subaru WRX / STI / Legacy GT / Forester XT 2002-2017

IAG Performance
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The IAG Stage 4 Short Block starts with brand new Subaru 2.5L engine case halves. IAG machines the case halves assembled together in our 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 in our in-house Sunnen SV-10. 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 (or Manley Billet add $1300) that is matched to ACL Race main bearings. Manley I-Beam and ARP2000 rod bolts are utilized along with ACL 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 by Manley Performance.
  • Connecting Rods - Manley I-Beam w/ ARP2000 Rod Bolts.
  • Rod / Main Bearings - ACL Race.
  • 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
  • Head Gaskets - JE Pro Seal .039 inch Head Gaskets - $96 or Cosworth 1.1mm - $222
  • 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.

Not planning on reusing your original short block service plugs and covers? IAG offers a simple comprehensive cover and seal kit that includes the (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 and (2) OEM wrist pin service cover screws. *If you are reusing your original wrist pin service plugs and covers always replace the (3) OEM wrist pin plug washers and (1) wrist pin service cover O-ring before installing a short block to avoid potential leaks. 

**All engines come in a pelican case which must be returned, free of charge, within 7 days of delivery. There will be a $250 fee if case not returned**


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