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.

The IAG 950 EJ25 Closed Deck Short Block features our propietary "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 passges and keeping them out of the combustion chamber. 14mm Head studs (Not Included) hold the assembly together.

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.

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.

The IAG 950 CNC Ported Race Cylinder Heads are designed for racing and competition. These fully CNC ported heads provide a significant upgrade in flow over the IAG 750 heads. These heads work great for cars where getting more power might be the difference between winning or losing that big race. The IAG 950 heads work great for drag racing, as well as high horsepower time attack or hill climb, and are designed to support up to 950 BHP with supporting mods. These heads include upgraded GSC +1MM Superalloy Valves, GSC Viton Valve Stem Seals, Upgraded GSC Valve Guides, IAG Beehive Valve Springs with Titanium Retainers, and OEM Keepers. GSC S2 Camshafts are available with OEM valve lifter buckets. We also offer an optional chamber modification service (see below) for EJ20 heads to allow use on EJ25 short blocks.

Each IAG 950 Cylinder Head Set starts with new OEM castings from Subaru of America. The first step is to select your Year and Model of vehicle so that we may provide you with the right castings to fit your project. Next, you'll select whether or not you want to include our optional GSC camshaft package. If selected, these heads will include new GSC S2 Camshafts and OEM Lifter Buckets for valve adjustment.

This IAG 950 fully CNC ported head package starts with brand new WRX STI OEM head castings directly from Subaru of America. The bare castings are visually inspected then fixtured into our in-house Centroid 5-axis CNC Machine. The Centroid CNC ports the intake and hard to reach exhaust "dog-leg" port runner. The benefit of CNC porting is not only an efficient way of machining the heads it also offers consistent port results that are hard to achieve by hand. Once the Centroid completes the port process the heads undergo a cam clearance machining process that removes material from the lifter area where large duration cam profiles are known to contact the castings. Shortly after the heads are drilled to fit larger 1/2" or 14mm head studs, which are commonly used in high horsepower builds. Next, the OEM guides are pressed out and replaced in favor of GSC Manganese-Bronze valve guides that are shaped to improve airflow. Once all the new intake and exhaust guides are in place they are diamond-honed in our honing station. The heads are then fixtured in our Newen 3.0 Valve Guide and Seat Machine to cut all intake and exhaust seats with a multi-angle valve job that suits the flow characteristics of GSC's +1mm valves. At this point, the heads' decks are resurfaced using our TS-3000 BlockMate which cuts the aluminum to a smooth even finish. Next, the heads are ultrasonically cleaned to remove debris and oils from the machining process. Finally, the heads are reassembled using IAG-Spec Beehive Valve Springs and Retainers along with GSC Viton stem seals.

Cylinder head porting has been around since the invention of the internal combustion engine. It can be done by hand with a die grinder and some cartridge rolls, and a seasoned professional can likely get a good result that way. Unfortunately, doing porting this way requires a lot of experience and care. One slip of the die grinder can ruin your cylinder head. This is where CNC porting comes in. Using our Centroid 5 axis CNC porting machine we can achieve the same results every time we put a set of heads into the machine. Every cylinder head comes out exactly the same and uses our race-proven, computer controlled, CNC porting program to guarantee results.

To get the most out of these heads we selected the GSC Power-Division billet S2 camshafts for your IAG 950 Head Package. These cams are built to suit the higher horsepower these heads will support. With a power range of 500 WHP and up, you need some additional supporting mods to utilize the true potential of the S2s. Our IAG 950 Short Block, an upgraded turbocharger and fuel system, and a quality engine management system are key. Along with the camshafts we'll include all new OEM valve lifter buckets and set final lash.

IAG's optional Chamber Modification Service is designed to reshape the combustion chamber of your cylinder heads to closely match the chamber of USDM STI cylinder heads to allow for use with 2.5L short blocks. This service is exclusive to USDM EJ20 2002-2005 WRX Cylinder Heads. IF YOU ARE NOT USING USDM HEADS ON A 2.5L EJ25 BLOCK, YOU DO NOT NEED THIS SERVICE.