IAG 550 2.5L Subaru Short Block For WRX, STI, LGT, FXT | EJ25

BUILT FOR BOOST

The IAG 550 Short Block is a sturdy upgrade designed for modified EJ25 Subarus capable of handling higher cylinder pressures created by increased boost. The IAG 550 Short Block features IAG Spec-H forged connecting rods with ARP2000 rod bolts, along with ACL or King race rod bearings and forged pistons. The OEM STI RA components simply aren’t built for the extra engine load of a larger turbocharger or an increase in boost pressure, creating a power ceiling that limits further modifications. The IAG 550 Short Block overcomes these shortcomings with high-performance internals capable of managing the extra stress, providing dependable performance and long-term durability for builds up to 550 bhp.

BUILT WITH 100% NEW COMPONENTS

Each IAG 550 Short Block starts with brand new EJ25 Subaru 2.5L, 99.75mm stock bore engine case halves for a sturdy foundation. The case halves are carefully measured and assembled using a new 2017+ Subaru 2.5L nitride treated STI crankshaft, which is matched to ACL or King race main bearings. The IAG 550 Short Block also features IAG Spec H-Beam Connecting Rods with ARP2000 rod bolts, along with ACL or King race rod bearings. The case halves are sealed with new OEM main case bolts and sealant. Finally, a set of IAG Spec JE 99.75mm Forged Pistons are carefully selected, measured, and installed to finish off the short block.

FORGED PISTONS

The IAG 550 Short Block features a set of IAG Spec JE 99.75mm forged pistons, a vast upgrade over the cast OEM pistons. These high-strength 2618 T6 alloy pistons are engineered to withstand the elevated cylinder pressures associated with increased boost. Their asymmetrical skirt design replaces the traditional full-round skirt, reducing weight while maintaining durability under heavy load. Smooth, flowing radii on the domes and dishes promotes improved flame travel and more efficient combustion. The pistons are securely fastened to the rods with .905 x 2.250" x .180" wall carbon steel wrist pins combined with Tru Arc locks. 

WHY UPGRADE?

In our experience one of the best aspects about an IAG engine is that they are hand built with meticulous attention to detail. An OEM short block can be a good option, but the hand built engines are best. At VEX we find the majority of OEM EJ25 engine failures stem from bearing issues, with spun rod bearings being the most common. These failures cause rapid, severe metal-on-metal wear, often resulting in catastrophic engine damage and spreading metal debris throughout the oil system. Another frequent issue is cracked piston ringlands, which typically occur when a vehicle has been modified and tuned for increased power while still running the OEM block. The IAG 550 upgraded forged connecting rods and rod bearings are significantly stronger than the OEM components, addressing these weaknesses and providing a solid foundation for a high-performance build.  

WARRANTY

While a new OEM block from Subaru doesn't come with a warranty when installed in a different vehicle, IAG Performance supports your purchase with a 12-month or 12,000-mile workmanship warranty for the IAG 550 Short Block. We take that even further to a 24-month, 24,000-mile workmanship warranty when purchased, installed, and tuned at the VEX Performance shop. Interested? Feel free to reach out and we’d be happy to provide a quote for installation.

INCLUDES:

• Case Halves: Brand new Subaru OEM case halves 99.75mm stock bore

• Pistons: IAG-Spec JE 99.75mm Forged Pistons, Ring Set, .180" Chromoly Pins, Clips, (Perfect Skirt Coating and Offset Wrist Pin)

• Connecting Rods: IAG-Spec H-Beam Rods with ARP2000 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 bolt

COMPRESSION RATIO:

• 9.3:1 on D Cylinder Heads (EJ255) w/ OEM Head Gasket

• 8.8:1 on B, V, and W EJ257 Heads w/ OEM Head Gasket

• 9.4:1 on S20 Cylinder Heads without Combustion Mod and with OEM Head Gasket

• 9.0:1 on D Cylinder Heads (EJ255) w/ .039" JE Proseal Head Gasket

• 8.5:1 on B, V, and W EJ257 Heads w/ .039" JE Proseal Head Gasket

• 9.1:1 on S20 Cylinder Heads without Combustion Mod and with .039" JE Proseal Head Gasket