Reinforced ARP bolts for OEM rods TOYOTA SUBARU 4U-GSE FA20

The engine concerned

The 2.0-litre flat-four (86 mm bore, 86 mm stroke, 1998 cc) is called 4U-GSE at Toyota and FA20 at Subaru: it is one and the same naturally aspirated engine, built from 2012 to 2021 for the Toyota GT 86, the Subaru BRZ and the Scion FR-S.

The original rod bolt, reference 12109AA100, is a single-use bolt with a diameter of 9.5 mm (M9.5 x 1.0).

Reinforced ARP bolts for connecting rods

Few parts of the bottom end work as hard as the rod bolt: at every revolution, it is what stops the cap from pulling away under the inertia loads of the rod and piston assembly. The original bolt is designed for stock power and is single-use.

These two kits, one per brand, each bring ARP2000 rod bolts that the ARP instruction sheet has you tighten by torque alone: the original rods of this application have blind holes, which rules out measuring the stretch. These bolts are made from ARP2000, an ARP-specific alloy steel heat treated to 220,000 psi tensile strength, with threads rolled once the treatment is complete. Classes 10.9 and 12.9 of standard fasteners start at 150,800 and 176,900 psi: ARP2000 exceeds them by 24 to 46%.

Technical specifications

The ARP instruction sheet asks you to check that there is an adequate chamfer around the bolt hole in the rod cap, so that the radius under the head has room to seat.

Tightening torque

Source of the torque and stretch figures: ARP 203-6302 and 260-6303 instruction sheets, in the revisions applicable at publication. The manufacturer's instruction sheets prevail in the event of any difference. Read the ARP 203-6302 instruction sheet; Read the ARP 260-6303 instruction sheet

Assembly is done without thread locker, as the ARP instruction sheet calls for none: ARP Ultra-Torque grease is applied to the threads and under the head of each bolt.

The ARP instructions for this kit require the big ends to be checked and resized once the fasteners are fitted: this job belongs to an equipped machine shop.

Technical guide

The torque value on this page assumes ARP assembly grease on the threads and under the bolt head; engine oil does not replace it.

The ARP brand

An engineer with an aerospace background, Gary Holzapfel launched ARP (Automotive Racing Products) in the early 1970s with one goal: to eliminate engine failures caused by weak fasteners in racing. ARP designs and manufactures thousands of part numbers in California, cylinder head, main and rod bolts, in several materials depending on the use, and has become known for the consistency of its manufacturing.

Vehicle compatibility

OEM reference (rod bolt): 12109AA100 (M9.5 x 1.0)

Why is it the most cost-effective solution?

On a GT 86 or a BRZ that is revved higher, each rod sees far greater inertia loads than in standard form, and a single bolt letting go wrecks the rod, the piston and the block. ARP2000 bolts secure this one point for far less than rebuilding a bottom end.

Matching connecting rod bearings

New bolts, new bearings: find below the connecting rod bearings suited to this engine.

Why not step up to forged connecting rods?

Hot forged under considerable pressure, generally from 4340 steel, a forged rod has a denser and more uniform structure than a stock rod. Against the original rod, frequently made of sintered metal and optimised for production cost, it brings about +19% yield strength, +8% tensile strength and +19 to +37% fatigue strength: enough to build a reliable high-power engine on. For your engine: