Reinforced head gasket Subaru Impreza Legacy 2.0 EJ20G EJ20GN

The Subaru engines covered

The EJ20G and EJ20GN are 2.0 litre (1,994 cc) petrol engines with four horizontally opposed cylinders, turbocharged. They power the Subaru Impreza (GC, GF) and Legacy I (BC, BF, BJ) listed below.

The original gasket carries the part number 11044-AA355. Subaru publishes neither its bore, its thickness nor its construction. A flat engine has two cylinder heads, so each engine takes two gaskets. Designed for the standard combustion pressure, it reaches its limit as soon as that pressure rises: the clamping load fades, the head lifts and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

Sealing also relies on the fasteners that clamp the head to the block, not only on the gasket. A composite gasket settles permanently beyond 100 N/mm²; the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and recovers its shape at every combustion.

This page brings together 19 part numbers from Cometic, the American competition gasket maker, for a single construction: MLS, a multilayer steel design. Eighteen gaskets (C4261) have a 93 mm bore and one (H1633SPL040S) has an 86 mm bore; thicknesses run from 0.69 to 3.56 mm, enough to adjust the compression ratio without touching the pistons or the cylinder head. As a rule, the gasket bore chosen is at least 0.5 mm larger than the actual cylinder bore. Each part number is sold individually and for one cylinder bank only: one is needed on the right and one on the left.

Technical specifications

A gasket's volume is the free space it leaves above each cylinder. It adds to the combustion chamber and lowers the compression ratio. Compare it only between gaskets of the same bore: here, 93 mm for the C4261 and 86 mm for the H1633SPL040S.

Preparation and fitting

Before fitting, run a straight edge over the head and the block to check they are flat, and have them resurfaced if needed. Cometic supplies these gaskets coated: add no sealant.

Technical guide

The construction offered

Cometic MLS Several stainless steel sheets, embossed and joined by rivets. The outer sheets carry active beads that surround each cylinder and each fluid passage. Moderate clamping is enough to seal and the bore distorts little: a versatile construction, from the tuned naturally aspirated engine to moderate boost.

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in 93 mm (C4261) and in 86 mm (H1633SPL040S).

Thickness. No thickness is published for the original gasket 11044-AA355. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

If you choose a thickness below the original one, use a dial gauge to measure how far the pistons protrude above the block's gasket face: this reading shows the clearance left between piston and head.

The brand

Founded in 1989 in Concord, Ohio, Cometic Gasket, Inc. is an American company that designs and makes engine gaskets and sealing parts. Its know-how is the custom gasket, cut to the bore and thickness requested, 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 93 mm and 86 mm bores of these gaskets 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-AA355.

Important: the part numbers on this page suit only the EJ20G and EJ20GN engines: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

The reinforced gasket takes over from the original once it has reached its limit: under greater combustion pressure it keeps its shape instead of crushing.

As soon as power is raised, with a bigger turbo, more boost pressure or a higher compression ratio, the head gasket becomes the weak link of the top end. A reinforced gasket avoids the leak and the head removal that follows, a job far costlier than the part.