Description

The IAG Stage 4 Tuff 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. 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 Tuff case is then drilled and tapped to accept 14mm head studs that combined with the IAG Fire-Lock head gasket set greatly reduces head gasket failure during high cylinder pressure scenarios. Next, the short block is 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 new 2017+ Subaru 2.5L nitride treated STI 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 new OEM main/case bolts and sealant (upgrading to ARP mains requires line honing).

Finally, IAG-Spec 99.75mm JE FSR 2618 Forged Pistons with electroless nickel plated tops and ring area as well as upgraded .250" / .906" H13 wrist pins are added to finish the Stage 4 Plus 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 H13 tool steel and 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 Tuff Closed Deck Includes:

  • Case Halves - Converted to Closed Deck using brand new Subaru OEM case halves, bored and honed to 99.75mm.
  • 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 - Machine case to fit 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" / .906" H13 Wrist Pins, Clips, (Perfect Skirt Coating and Offset Wrist Pins)
  • Connecting Rods - IAG-Spec Tri-Beam +2mm w/ ARP 625+ Rod Bolts.
  • Rod / Main Bearings - ACL or King Race bearings.
  • Crankshaft - Standard New Subaru Nitride Treated 2017+ STI Crankshaft.
  • Case / Main Bolts – Standard FHI Subaru case bolts.

Power:

  • The IAG Stage 4 Tuff Short Block has a power output rating of 1000BHP.

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 (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.

Specifications

Compatibility

Note: Additional modification required for EJ20 heads. Please consult engine builder if using EJ20 heads to account for correct valve clearance and compression

  • 2001-2014 Subaru WRX
  • 2002-2020 Subaru STI
  • 2004-2009 Subaru Liberty GT
  • 2003-2013 Subaru Forester XT

The IAG Stage 4 Tuff 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. 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 Tuff case is then drilled and tapped to accept 14mm head studs that combined with the IAG Fire-Lock head gasket set greatly reduces head gasket failure during high cylinder pressure scenarios. Next, the short block is 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 new 2017+ Subaru 2.5L nitride treated STI 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 new OEM main/case bolts and sealant (upgrading to ARP mains requires line honing).

Finally, IAG-Spec 99.75mm JE FSR 2618 Forged Pistons with electroless nickel plated tops and ring area as well as upgraded .250" / .906" H13 wrist pins are added to finish the Stage 4 Plus 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 H13 tool steel and 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 Tuff Closed Deck Includes:

  • Case Halves - Converted to Closed Deck using brand new Subaru OEM case halves, bored and honed to 99.75mm.
  • 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 - Machine case to fit 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" / .906" H13 Wrist Pins, Clips, (Perfect Skirt Coating and Offset Wrist Pins)
  • Connecting Rods - IAG-Spec Tri-Beam +2mm w/ ARP 625+ Rod Bolts.
  • Rod / Main Bearings - ACL or King Race bearings.
  • Crankshaft - Standard New Subaru Nitride Treated 2017+ STI Crankshaft.
  • Case / Main Bolts – Standard FHI Subaru case bolts.

Power:

  • The IAG Stage 4 Tuff Short Block has a power output rating of 1000BHP.

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 (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.

Note: Additional modification required for EJ20 heads. Please consult engine builder if using EJ20 heads to account for correct valve clearance and compression

  • 2001-2014 Subaru WRX
  • 2002-2020 Subaru STI
  • 2004-2009 Subaru Liberty GT
  • 2003-2013 Subaru Forester XT

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