Forged connecting rods Subaru - 2.0L 16V - FA20 for forged pistons

The Subaru FA20 engine

The Subaru FA20 is a 2.0-litre, 16-valve flat-four (boxer), launched in 2012 and jointly developed by Subaru and Toyota. Its compact H4 architecture pairs a "square" 86 mm bore with an 86 mm stroke (1,998 cc), with dual overhead camshafts per bank and variable valve timing. It comes in two families: the naturally aspirated FA20 (badged 4U-GSE by Toyota), with D-4S dual injection and a 12.5:1 compression ratio, producing around 200 hp; and the direct-injection turbo FA20DIT (10.6:1), delivering 241 to 268 hp depending on the model.

Built from 2012 to 2021, the FA20 powers the Subaru BRZ sports coupe and its Toyota GT86 / 86 twins in naturally aspirated form, while the FA20DIT equips the WRX, the Forester XT and the Levorg. A rev-happy boxer that is hugely popular for tuning, it nonetheless sees its factory connecting rod reach its limits quickly as power climbs, especially on the turbocharged versions and high-torque builds. That is exactly where forged connecting rods come in.

Forged connecting rods

Machined from high-strength 4340 steel, forged connecting rods reinforce the bottom end as soon as torque and engine speed rise. They become essential when switching to forged pistons, raising the rev limit, increasing displacement or building a high-output engine, where the stock rod quickly reaches its limits. Designed to absorb the severe mechanical loads of tuned engines, naturally aspirated as well as forced-induction, they cover every discipline (rally, drift, drag, circuit and track days, hillclimb, time attack) and support Stage 2, Stage 3 and Stage 4+ builds, right up to full race engines.

Forged 4340 steel: what is it?

4340 is a low-alloy nickel-chromium-molybdenum steel, used in aerospace as much as in motorsport. Hot-forged then heat-treated (quenched and tempered), it combines a high yield strength, outstanding fatigue endurance and preserved ductility. Compared with a stock rod (often sintered metal, designed for production cost), a forged 4340 rod gains roughly +19% in yield strength, +8% in tensile strength and, above all, +19 to +37% in fatigue endurance, for a service life under repeated loads several times longer. That is why forged 4340 is the benchmark as soon as engine speed and combustion pressure rise.

Connecting rod profiles

	I-3P profile. Boostline’s three-pocket I-beam (3-Pocket) design: material is distributed precisely to deliver high stiffness and excellent buckling resistance while keeping mass low. Engineered for heavily boosted engines, it withstands high torque levels without weighing down the reciprocating assembly.
	H profile. Its H-section favours resistance to compression and bending: it is the preferred profile for high-torque engines and drag use. The H-HD (Heavy Duty) variant further strengthens the rod body for the most demanding builds.
	I-HD profile. Its narrower central I-section lightens the rod (less inertia, sharper rev climbs); the I-HD (Heavy Duty) version is a reinforced one, built for the high-revving turbo engines of Manley’s Pro Series Turbo Tuff range.

Technical specifications of the rods

Tightening torque and stretch

How to choose your rod bolts?

The rod bolt is one of the most heavily loaded parts in an engine. The key is to match the ARP grade to the real use of the build, then to scrupulously respect the assembly torque and stretch.

	ARP 2000 (tensile strength of about 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 storage constraints.
	ARP Custom Age 625+ is the extreme grade: its tensile strength reaches ~260,000 to 280,000 psi (~1,793 to 1,931 MPa). Immune to hydrogen embrittlement, it targets very heavily loaded engines (high boost, high torque, drag use) where the maximum safety margin is sought, with no storage constraints.

Measuring bolt stretch

Buy the ARP stretch gauge →

Technical guide

The brands offered

Boostline is an American brand of high-performance forged connecting rods. Forged from 4340 steel, its rods use the patented I-3P (three-pocket I-beam) profile sized for heavily boosted engines: high stiffness, buckling resistance and a wide safety margin, without penalising mass. It is offered here with ARP 2000 or ARP Custom Age 625+ hardware.

Manley (Manley Performance) is one of the historic American manufacturers of motorsport engine parts. Its forged 4340-steel rods, weighed and matched, are available here in H / H-HD (Heavy Duty) profile and in I-HD profile (Pro Series Turbo Tuff range), with ARP 2000 or ARP Custom Age 625+ hardware. A safe bet for high-torque, high-rpm turbo builds.

Glossary

1) Small end  2) Small-end diameter  3) Rod beam  4) Rod bolt  5) Big end  6) Rod nut / bolt  7) Rod cap  8) Big-end diameter  9) Center-to-center

Vehicles compatible with the Subaru FA20 engine

OEM reference: (set of 4 rods).

Why it is the most cost-effective solution

When a stock bottom end fails (a broken, bent or scored rod), simply returning to the factory configuration means replacing the rods and, more often than not, the damaged pistons at the same time: the bill climbs quickly for a standard repair. For a comparable budget, sometimes lower, forged 4340-steel rods combined with forged pistons deliver far greater reliability and safety margin, plus genuine headroom for power increases. It has been the choice of European tuners for more than fifteen years: for the same spend, more reliability, more potential and more longevity.