IAG Stage 4 TUFF Closed Deck Short Block

2004-2021 STI / 2006-2014 WRX

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SKU: IAG-ENG-1452We price match!

On order from MFG
Average time to ship: 36 business days

IAG Stage 4 Tuff EJ25 Subaru Closed Deck Short Block 2015-2021 Subaru STI

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IAG Stage 4 Tuff EJ25 Subaru Closed Deck Short Block 2015-2021 Subaru STI


  • Brand new Subaru OEM case halves converted to Closed Deck 
  • IAG Fire-Lock receiver groove machining
  • Bored and honed to 99.75mm
  • IAG-Spec JE FSR 99.75mm 2618 Forged Pistons
  • .250" / .927" H13 Performance wrist pins, clips
  • IAG Spec Tri-Beam +2mm connecting rods
  • ARP625+ Rod bolts
  • ACL Rod and Main Bearings
  • Standard new Subaru Nitride Treated 2017+ STI crankshaft
  • Standard FHI Subaru case bolts/main bolts
  • Machined to accept 14mm head studs (head studs sold separately)
  • Requires IAG Fire-Lock Head Gaskets
  • Rated to 1000 HP with supporting modifications



  • 8.2:1 on B, V, and W cylinder heads (EJ257)
  • 8.5:1 on D cylinder heads (EJ255)



The IAG Performance Stage 4 Tuff EJ25 Subaru Closed Deck Short Block is a pre-assembled short block assembly performed by one of the leading power innovators in the Subaru motorsports community. This block begins with brand new Subaru 2.5L case halves that are assembled at IAG's facility using their state-of-the-art milling machines. These are machined to accept IAG's closed-deck inserts that transform the deck into a solid deck. The case halves then get machined for IAG's Fire-Lock head gaskets that are loosely derived from diesel technology where a counterbore step is machined around each cylinder bore to allow specialty-sized fire rings to drop into the machined area and head gasket bores.

The Stage 4 Tuff case is then drilled to accept 14mm head studs that are combined with the IAG Fire-Lock head gasket set which greatly reduces the chances of head gasket failure during high-cylinder pressure scenarios. The clock is then deck plate bored and honed to 99.75mm using IAG's in-house Sy=unnen SV-30 which is the most advanced automotive cylinder hone available. The engine is then assembled using the strongest ingredients that can sustain up to 1000 HP with the right supporting modifications, which is ideal for those of you looking to make a large number on the dyno, drag strip, or to endure high-stress conditions with road racing or rally. 






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