Forged connecting rods Subaru / Toyota - 2.0L 16V Boxer - FA20 / 4U-GSE (BRZ / GT86) for forged pistons

The Subaru FA20 / Toyota 4U-GSE 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.

Technical specifications of the rods

Tightening torque and stretch

Technical guide

Forged 4340 steel: what is it?

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.

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 ~220,000 psi, i.e. ~1,517 MPa) is the standard fitment on all three rods of this FA20 / 4U-GSE boxer: 3/8"-41 mm on the Boostline I-3P, 3/8"-38 mm on the Manley H-HD and I-HD. The grade is rated up to 200 hp per cylinder in 3/8" and up to 8,500 rpm, which makes it the usual choice for circuit racing, trackdays, drift, rally, drag and hillclimb. With a short 129.3 mm centre-to-centre, the bolt works in a confined space, one more reason to fit it cleanly: threads blown out and lubricated, tightening in passes and preload brought up to the stretch measured with a dial gauge. No storage constraint, and a free-length check at every teardown is enough to clear it for reuse.

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

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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 / Toyota 4U-GSE engine

Listed below are the vehicles equipped with the Subaru / Toyota 2.0L 16V Boxer FA20 / 4U-GSE engine. Before ordering, take the piston pin diameter and the rod length from the engine concerned. Variant concerned: BRZ / GT86.

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.