Reinforced ARP main bolts for SUBARU TOYOTA FA20

The Subaru FA20 and Toyota 4U-GSE engines concerned

ARP lists this part number for the 2.0-litre Subaru FA20 engine, a flat-four with double overhead camshafts. The compatibility table covers the models that use it (Toyota GT86 under the 4U-GSE code, Subaru BRZ, Scion FR-S), taken from the NGK parts catalogue.

This kit replaces the original main bolts of the block, whose factory part number is not published in our sources and is therefore not shown here. For the same engine under its Toyota designation, ARP offers a separate part number, kit 203-5002.

Reinforced ARP bolts for main bearings

The bottom end rests on its main bearings: combustion after combustion, the loads coming from the connecting rods end up on them. Under this stress the main cap tries to move on its parting line, which eventually brinells the mating faces and distorts the bearing bore.

This kit brings together the ARP Pro Series main bolts for the FA20, 10 mm and 8 mm bolts that the ARP catalogue lists among the crankcase through-bolt kits. The instruction sheet calls for hand-threading, lubricating the underside of the head, the washers and the threads with ARP Ultra-Torque, then tightening in three equal steps. It states the direction of the chamfered washer, chamfer facing the bolt head: fitting it the wrong way round causes premature failure. The number of pieces is not stated. These bolts are made of Inconel 718, a nickel-based alloy for which the ARP catalogue gives a tensile strength of 210,000 to 230,000 psi, with no sensitivity to hydrogen embrittlement or corrosion. These Inconel bolts in M10 and M8 take up to 600 hp on this four-cylinder engine (calculated estimate).

Technical specifications

Tightening torque

Each bolt holds the cap by tightening into the block thread; tightening is done to torque, in several stages, with ARP grease on the threads and under the head.

Follow the cap tightening sequence recommended by the manufacturer when bringing the bolts up to torque; the kit's instruction sheet details each step.

Stronger fasteners change the clamping force: the size and roundness of the main bearing bores are checked after installation, and the bores are align honed if necessary, using the final fasteners and lubricant.

Values taken from the ARP 260-5001 instruction sheet in force at the date of publication; the official instruction sheet prevails should any difference appear. Read the ARP 260-5001 instruction sheet

Technical guide

The torque figures given only apply with ARP assembly grease, never with engine oil.

The ARP brand

Founded in the early 1970s by Gary Holzapfel, who came from the aerospace industry, ARP (Automotive Racing Products) set out to prevent fastener-related engine failures in motorsport. Its thousands of part numbers are designed and manufactured in California, in materials chosen for each use.

When to upgrade the main bearing fasteners

• Subaru BRZ, Toyota GT86 or Scion FR-S built beyond its standard output
• FA20 engine stripped to fit a forged crankshaft, reinforced rods or pistons
• Main bearing bores to be measured, then aligned if necessary, before fitting reinforced fasteners
• Frequent track, drift or competition use at high revs
• Complete engine rebuild with replacement of the original main bolts

Vehicle compatibility

Why is it the most cost-effective solution?

A BRZ or a GT86 built for more power loads the main bolts far beyond their original duty. An ARP Inconel kit weighs little in the budget compared with a block to rework and a crankshaft to replace.

Consider the crankshaft main bearings

To complete the bottom end overhaul, consider the tri-metal crankshaft main bearings suited to these engines: