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5 in stock



Stage 2 Short Block H-Beam Connecting Rods


The IAG 950 Short Block is the ultimate “weekend racer” block. Built to withstand up to 950 BHP, this is our strongest “Street” short block offering. The IAG 950 short block features +2mm IAG Spec H-Beam forged connecting rods, IAG-Spec JE Pistons with electroless nickel plated coating with H13 tool steel wrist pins, and our venerable “Fire-Lock™” head gasket system for 14mm head studs. Each IAG 950 short block is hand assembled using ACL or King rod and main bearings. This combination of parts makes the IAG 950 the perfect block for drag or road racing.



The IAG 950 Short Block starts with brand new Subaru 2.5L engine case halves. Our machinists machine the assembled case halves in our Haas VF-4SS CNC mill to accept the IAG Closed Deck inserts, transforming the block into a solid deck. Next, a deck pair of deck plates are attached and the short block is bored and honed to 99.75mm in our in-house Sunnen SV-30 computer controlled cylinder hone. IAG’s in-house honing process allows us to set custom piston to wall clearances to ensure quiet operation and reduced oil consumption. The Haas mill also cuts a groove at the top of each cylinder to accept the Fire-Lock™ head gasket rings and drills each head bolt hole for 14mm head studs. The modified case halves are then assembled using a new 2017+ Subaru 2.5L nitride treated STI crankshaft and IAG-Spec Tuff H-Beam connecting rods with ARP rod bolts. IAG Short blocks feature ACL or King Race rod and main bearings and are all balanced and blueprinted. Finally, the case halves are sealed with new OEM main/case bolts and sealant.

IAG Fire-Lock Head Gasket System


The IAG 950 EJ25 Closed Deck Short Block features our proprietary “Fire-Lock™” Head gasket system. This system has been proven in our record setting race cars to be the strongest Subaru head gasket system ever produced. To achieve these results our engineers separated the combustion chamber sealing from the fluid sealing aspects of the head gaskets. Our machinists carefully machine a lip at the top of each cylinder to accept the “Fire-Lock™” ring. With the ring locked in place, it stands proud above the deck, providing a superior seal. The separate gasket bodies take care of sealing oil and coolant passages and keeping them out of the combustion chamber. 14mm Head studs (Not Included) hold the assembly together.


IAG 950 Closed Deck Block


Our unique closed deck system significantly increases the strength of the OEM case halves. This process supports the cylinder walls at the top of the case in order to prevent flexing and possible cracking where the case bolt reliefs are cut into the back of the cylinder wall.
During the installation process we machine the assembled case halves in our Haas VF-4SS CNC mill to accept the IAG Closed Deck inserts. Once the case has been machined we heat it in an oven while freezing the specially machined inserts with liquid nitrogen. The inserts are then pressed into place and then machined to a mirror finish.
The unique inserts feature small passages that allow needed coolant flow to the deck surface. This means that the closed deck system does not affect the block’s cooling ability and will not cause overheating, even in daily drivers.

IAG 950 IAG-SPec JE Pistons and Rings


The pistons used in the IAG 950 Short Blocks are specifically designed to support the rigors of racing. Designed in partnership with JE, these IAG-Spec pistons feature electroless nickel plating and a 2618 Alloy. Extra thick ring lands resist collapsing under pressure. The upgraded .250″ wall H13 tool steel offset wrist pins are designed to hold up to 950 BHP without bending or breaking. The pistons also feature JE’s Perfect Skirt coating.


IAG 950 Closed Deck EJ25 Short Block 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
  • Head Studs –Machine Case for 14mm head studs – *Head studs are 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 Tuff H-Beam +2mm / 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.

Compression Ratio:

  • 8.5:1 on D Cylinder Heads (EJ255)
  • 8.2:1 on B, V and W EJ257 Heads with standard thickness gasket.

Power: The IAG 950 Short Block has a power output rating of 950 BHP

Head Gasket Required:

After years of research and development testing, the IAG Performance Fire-Lock™ head gasket is the newest solution to preventing head gasket failure on high horsepower and high boost Subaru EJ25 engines. This solution 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 shims are designed to create a compression seal once the heads are installed and torqued into place. IAG fire rings are manufactured to a very strict tolerance from a proprietary alloy and are then put through a heat treatment process. The gaskets are manufactured from an asbestos-free composite raw material and feature a silicone based beading applied to critical areas to improve sealing around all water and oil passages. The combination of the alloy compression shims and gaskets assure maximum sealing for a Subaru EJ25 turbocharged engine.
*The IAG Fire-Lock™ gaskets require machine work for installation and are recommended for use with 14mm head stud hardware.

*The gaskets are sold in pairs with four Fire-Lock™ rings.

  • Composite Material
  • IAG-Spec Alloy Ring
  • Specifically designed for 14mm Head Studs
  • Silicone Beading
  • 100mm Bore
  • .051″ Thickness
  • Intended for High Horsepower, High Boost applications
  • IAG ARP 14mm Head Studs Required
  • Gaskets sold in pairs
    Install Notes:

1. If a block or cylinder head was previously o-ringed the groove must be filled and resurfaced before using this type of gasket.
2. These gaskets require IAG ARP 14mm head studs to achieve the required torque necessary for proper installation.
3. Due to the required torque, any block that was previously honed will need to go to the next size overbore.
4. Future servicing will require cylinder head resurfacing due to an imprint left from the Fire-Lock™ rings.

  • *IAG Fire-Lock™ .051″ Head Gaskets with IAG-Spec Alloy Ring Set* PN# IAG-ENG-1740 – Add to your order for an extra $299.99

14mm Head Studs Required:

  • IAG / ARP 14mm Head Stud Set Part# IAG-ENG-1711 – Add to your order for an extra $579.99


Hardware / Seal Option:

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 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. *Never reuse a rear main seal on a new short block. – Add to your order for an extra $125.99


Availability: Usually Ships in 2 to 3 Weeks