Reinforced head gasket Subaru 2.0 FA20F

The Subaru engines covered

The FA20F is Subaru's 2.0 litre petrol engine: a flat four with sixteen valves, direct injection and a turbocharger. It powers the Forester, Impreza, WRX and Outback listed in the compatibility table below. Each cylinder head takes its own gasket, left or right, so the engine needs two, one of each part number.

The original gaskets carry part number 11044-AA821 on the right (it replaces 11044-AA820) and 10944-AA110 on the left. Subaru publishes neither their bore, nor their thickness, nor their construction. Sized for standard combustion pressure, they give up once it rises: clamping load drops, the head lifts and coolant passes into a cylinder.

Reinforced cylinder head gaskets

Sealing does not rest on the gasket alone: the fasteners clamping the head to the block contribute just as much. A composite gasket settles for good beyond 100 N/mm²; the 301 stainless steel of an MLX gasket withstands 517 N/mm², 5 times more, and regains its shape on every combustion stroke. Replace any stretched or marked head bolts.

This page presents the two part numbers from Cometic, an American maker of racing gaskets, in a single construction: the MLX, three-layer stainless steel. The C4954-032 fits on the left and the C4955-032 on the right. The bore is 89.5 mm and the thickness 0.81 mm, or 0.032 inch. Each part number is sold individually: order one for each side.

Technical specifications

A gasket's volume is the free space it leaves above each cylinder. It adds to the combustion chamber: the larger it is, the lower the compression ratio. Both part numbers on this page share the same 89.5 mm bore and the same thickness.

Preparation and fitting

Before refitting, run a straight edge over the cylinder head and the block to check they are flat, and have the surfaces machined if needed. Cometic gaskets arrive already coated: do not apply any sealing paste.

Technical guide

The construction offered

Cometic MLX A stack of three embossed, riveted stainless steel sheets, the centre sheet being folded back to form a stopper around the combustion chamber, under a high-temperature coating. Clamping load rises at that point without distorting the bore any further. It is the strongest of the all-steel constructions, suited to hard-pushed forced induction. The part numbers C4954-032 and C4955-032 on this page are offered in this construction.

Choosing bore and thickness

Gasket bore. The Cometic MLX is offered here only in 89.5 mm, for both sides: C4954-032 on the left, C4955-032 on the right.

Thickness. Subaru publishes no thickness for the original gaskets 11044-AA821 and 10944-AA110. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

As the original thickness is not published, use a dial gauge to measure how far the pistons stand above the block's gasket face, especially if the removed gasket is thicker than 0.81 mm: this reading gives the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American company founded in 1989 in Concord, Ohio, which designs engine gaskets and sealing solutions. It made its name with the made-to-order gasket, cut to the bore and thickness required, produced in the United States from American raw materials.

Advantages over the original gasket

When a reinforced gasket becomes necessary

• Adding forced induction, or raising boost on an already turbocharged engine
• Cylinder rebored beyond what the 89.5 mm bore of the gasket offered covers
• Looking for a compression ratio different from standard, higher or lower
• Engine that has already lost its gasket, or is consuming coolant
• Competition use, where the gasket goes through repeated temperature rises

Vehicle compatibility

OEM part number: 11044-AA821 (right, replaces 11044-AA820) and 10944-AA110 (left).

Important: the part numbers on this page only suit the FA20F engine; the naturally aspirated FA20 of the BRZ and GT86 takes other gaskets: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

When the standard gasket reaches its limit, the reinforced gasket takes over: under higher combustion pressure it keeps its shape instead of settling.

With a bigger turbo, higher boost or more compression, the head gasket is the first part of the top end to suffer. On an engine that is already turbocharged like the FA20F, a reinforced gasket limits the risk of a leak and spares an expensive head removal.