Forged long connecting rods Subaru - 2.0 / 2.5L 16V Turbo Boxer EJ205 EJ257 (132.5 mm center-to-center) for forged pistons

The Subaru EJ turbo engine (EJ205 / EJ257)

Subaru’s EJ is a flat-four (boxer) introduced in 1989 and built until 2021, built around an aluminium crankcase and a five-bearing crankshaft. While the family spans 2.0 l (EJ20), 2.2 l (EJ22) and 2.5 l (EJ25) units in both single and double overhead-cam 16-valve form, it is the turbocharged versions that forged the brand’s motorsport reputation: the 2.0 l EJ205 “Phase 2” and the 2.5 l EJ257 with semi-closed deck and AVCS variable valve timing. They power the Impreza WRX and WRX STi as well as the turbo Forester, from the World Rally Championship to circuit and time attack builds.

The EJ boxer takes boost willingly, but its stock rod becomes the weak link as soon as boost pressure and torque climb: beyond 350 to 400 hp it bends or breaks. Switching to forged rods then becomes essential to make the bottom end reliable. The rods shown here use a long 132.5 mm center distance, about 2 mm more than the stock figure (130.5 mm): combined with reduced-compression-height pistons, this long center distance raises the rod/stroke ratio and limits side loads on the skirts, a favoured choice for hard turbo builds on the EJ205 and EJ257.

Forged connecting rods

Machined from high-strength 4340 steel, forged rods reinforce the bottom end as soon as torque and engine speed rise. They become essential when fitting forged pistons, increasing displacement, raising the rev limit or undertaking an ambitious build, where the stock rod quickly reaches its limits. Designed to absorb the extreme mechanical loads of built engines, naturally aspirated or boosted, they cover every discipline: rally, drift, drag, circuit and track days, hillclimb, time attack. They suit Stage 2 and Stage 3 builds as well as Stage 4 and beyond, up to full race engines.

Forged 4340 steel: what is it?

4340 is a low-alloy nickel-chromium-molybdenum steel used in aerospace as well as motorsport. Hot-forged then heat-treated (quench followed by tempering), it combines a high yield strength, excellent fatigue endurance and preserved ductility. Compared with a stock rod, usually sintered or cast then machined for mass production, a forged 4340 rod offers markedly higher strength and fatigue life: its fibrous grain follows the part’s outline and removes crack initiation points, allowing far higher loads and engine speeds with no compromise on reliability.

Connecting rod profiles

	H profile. Its H-shaped section favours resistance to compression and bending: it is the profile of choice for high-torque engines and drag use. The H-HD (Heavy Duty) version thickens the sections and reinforces the small-end/big-end assembly to take higher loads, ideal on hard-working turbo EJ engines.
	I / I-HD profile. Its narrower central I-section lightens the rod (less inertia, sharper rev pick-up). The I-HD version (Heavy Duty, Manley Pro Series Turbo Tuff range) is a high-end reinforcement designed to combine lightness and strength on high-rpm turbo builds.

Technical specifications of the rods

Tightening torque and stretch

How to choose your rod bolts?

Bolt choice governs how the assembly holds together: the rod bolt sees considerable cyclic loads and must keep its preload at every engine speed. The grade should therefore be chosen according to the power actually targeted, then the tightening torque and stretch must be followed scrupulously.

	ARP 2000 (tensile strength around 220,000 psi, i.e. ~1,517 MPa) is the high-performance standard. It covers builds up to 150 hp per cylinder in 5/16" or 200 hp per cylinder in 3/8", and up to 8,500 rpm. It is the most versatile grade, with no particular storage constraint.
	ARP Custom Age 625+ is the extreme grade: its tensile strength reaches roughly 260,000 to 280,000 psi (~1,793 to 1,931 MPa). Immune to hydrogen embrittlement, it targets very heavily stressed engines (big boost, high torque, drag use) where maximum safety margin and the best fatigue life are sought.

Measuring bolt stretch

Buy the ARP stretch gauge →

Technical guide

The brands offered

Manley (Manley Performance) is one of the historic American manufacturers of competition engine parts. Its forged 4340-steel rods, weighed and matched, are offered here in H / H-HD (Heavy Duty) profile and I-HD profile (Pro Series Turbo Tuff range), with ARP 2000 or ARP Custom Age 625+ bolts. Available with a long 132.5 mm center distance for the specific builds of the EJ205 and EJ257, they are a safe bet for high-torque, high-rpm turbo builds.

Glossary

1) Small end 2) Small-end bore 3) Rod body 4) Rod bolt 5) Big end 6) Rod nut / bolt 7) Rod cap 8) Big-end bore 9) Center distance

Vehicle compatibility of Subaru EJ engines

Why this is the most economical solution

When a stock bottom end lets go (a broken, twisted or scored rod), simply returning to the factory configuration means replacing the rods and, more often than not, the pistons damaged in the process: the bill climbs fast for a standard rebuild, with no gain in reliability. For a comparable budget, sometimes lower, forged 4340-steel rods combined with forged pistons turn the bottom end into a durable assembly able to withstand boost and high engine speeds. The investment is better placed: you don’t just repair, you make it reliable, and you avoid another failure.

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