An IAG short block is an excellent foundation for building a performance Subaru engine.

For my 2002 Subaru WRX Wagon, I chose to build off of the IAG Stage 2.5 Subaru EJ25 Closed Deck Short Block.

I used the original 2-liter heads and paired them to the 2.5-liter block making what Subaru enthusiast call a hybrid build.

The block and heads were machined by IAG and the engine was built at Just-N-Tyme Performance in Fredericksburg Virginia.

IAG Short Block Engine Build - Wills WRX Wagon

IAG Performance is a Subaru performance parts, service and tuning facility in Baltimore, Maryland. Established in 2004, IAG has built a solid reputation in the automotive performance industry.

IAG Short Block Engine Build - Wills WRX Wagon - Image 2

IAG Short Block Horsepower

The original goal for the build was power equivalent to a WRX STI. I was heavily considering doing a full STI swap into the car, but the costs start rising real fast when you add wiring harnesses and dash swapping. It was going to be cheaper in the short term to use an IAG short block and I would have the option to increase the horsepower drastically in the future. The IAG short block can handle 675 BHP. A used STI engine would find limits well before 675 BHP.

IAG Short Block Engine Build - Wills WRX Wagon - Image 3

IAG Short Block Details

The following details are from IAG for the Stage 2.5 Subaru EJ25 Closed Deck Short Block:

“The IAG Stage 2.5 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-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. IAG-Spec Tuff H-Beam connecting rods and ARP 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 .180″ Chromoly Wrist Pins are added to finish the Stage 2.5 short block.”


Full Build List For The WRX Engine


  • IAG Stage 2.5 Closed Deck Short Block
  • OEM Subaru 2.0 L Cylinder Heads Machined by IAG
  • Cosworth Head Gaskets
  • ARP Head Stud Kit / Subaru
  • GSC P-D EJ series EJ205/EJ207/EJ257 Chrome Polished Super Alloy Exhaust Valve-32mm Head(STD)-SET 8
  • GSC P-D Subaru EJ Series EJ205/EJ207/EJ257 Chrome Polished Intake Valve – 36mm Head (STD) – SET 8
  • NGK Iridium Spark Plugs
  • Cobb Air Oil Separator
  • Orbit Oil Pump
  • CSF Racing Radiator With Built-In Oil Cooler and CSF Sandwich Plate
  • Mishimoto Radiator Hoses
  • Blouch Dominator Turbo (1.5xt-r 10cm^2)
  • COBB Boost Controller
  • Perrin Turbo Inlet
  • Grimmspeed Top Mounted Intercooler (TMIC)
  • Grimmspeed Y-pipe
  • Torque Solutions TGV
  • Injector Dynamics 1050cc Injectors
  • Injector Dynamic Injector Pigtail
  • AEM 320lph Fuel Pump
  • Torque Solutions Fuel Rails – black
  • Just-N-Tyme Performance Built Fuel Lines
  • Aeromotive Adjustable EFI Regulator
  • Aeromotive Fuel Pressure Gauge
  • Agency Power Unequal Headers
  • Invidia 02-07 WRX/STi Bell Mouth Downpipe
  • Grimmspeed Uppipe 44mm EWG V-Band w/ Black Ceramic Coating
  • Turbosmart 45mm External Wastegate – Black
  • GESI HO-Series Catalytic Converter 3″ Inlet/Outlet x 4″ O.D. x 7″ Overall Length (rated for 350-500HP)
  • Custom Just-N-Tyme Performance Catback Exhaust