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3.0L 24v - EZ30D
Manufacturers
3.0L 24v - EZ30D
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Reinforced Athena O-Ring and Cometic MLS head gasket for the Subaru EZ30D 3.0-litre flat-six engine, one part number per cylinder bank.
The Subaru EZ30D is a 3.0-litre, 24-valve flat-six (boxer) petrol engine fitted to the Subaru Outback (BH and BP) listed in the table below. Each bank of three cylinders has its own head and gasket: one is needed on the right and one on the left.
Subaru gives two part numbers for the original gasket, 11044AA603 for gasket no. 1 and 10944AA003 for gasket no. 2, one per bank, but publishes neither the bore, nor the thickness, nor the construction. They are rated for standard combustion pressure: when it rises, the clamp load relaxes, the head lifts and coolant reaches a cylinder.
A cylinder head gasket does not seal on its own: it holds because the fasteners press the head against the block. A composite gasket is crushed for good beyond 100 N/mm² of allowable stress, whereas the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and springs back with every combustion. The O-Ring shares the roles differently: its stainless ring alone seals the combustion, the body handles the water and oil circuits, and nothing has to be machined in the block.
This page gathers the part numbers of two competition gasket makers, Athena and Cometic, in two constructions: O-Ring with a stainless ring and multi-layer steel MLS. The gasket bore is 90 mm and thicknesses range 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.
| Gasket bore | Thickness | Gasket volume | Gasket type OEM not specified | Brand | Part number OEM 11044AA603 et 10944AA003 |
| 90 mm | 0.69 mm | 4.39 | MLS | Cometic | C5860-027 |
| 90 mm | 0.69 mm | 4.39 | MLS | Cometic | C5861-027 |
| 90 mm | 0.76 mm | 4.83 | MLS | Cometic | C5860-030 |
| 90 mm | 0.76 mm | 4.83 | MLS | Cometic | C5861-030 |
| 90 mm | 0.91 mm | 5.79 | MLS | Cometic | C5860-036 |
| 90 mm | 0.91 mm | 5.79 | MLS | Cometic | C5861-036 |
| 90 mm | 1.00 mm | 6.36 | O-Ring | Athena | 330166R |
| 90 mm | 1.00 mm | 6.36 | O-Ring | Athena | 330167R |
| 90 mm | 1.02 mm | 6.49 | MLS | Cometic | C4623-040 |
| 90 mm | 1.02 mm | 6.49 | MLS | Cometic | C4624-040 |
| 90 mm | 1.02 mm | 6.49 | MLS | Cometic | C5860-040 |
| 90 mm | 1.02 mm | 6.49 | MLS | Cometic | C5861-040 |
| 90 mm | 1.14 mm | 7.25 | MLS | Cometic | C5860-045 |
| 90 mm | 1.14 mm | 7.25 | MLS | Cometic | C5861-045 |
| 90 mm | 1.30 mm | 8.27 | MLS | Cometic | C5860-051 |
| 90 mm | 1.30 mm | 8.27 | MLS | Cometic | C5861-051 |
| 90 mm | 1.30 mm | 8.27 | MLS | Cometic | H3027051S |
| 90 mm | 1.30 mm | 8.27 | MLS | Cometic | H3570051S |
| 90 mm | 1.42 mm | 9.03 | MLS | Cometic | C5860-056 |
| 90 mm | 1.42 mm | 9.03 | MLS | Cometic | C5861-056 |
| 90 mm | 1.52 mm | 9.67 | MLS | Cometic | C5860-060 |
| 90 mm | 1.52 mm | 9.67 | MLS | Cometic | C5861-060 |
| 90 mm | 1.68 mm | 10.69 | MLS | Cometic | C5860-066 |
| 90 mm | 1.68 mm | 10.69 | MLS | Cometic | C5861-066 |
| 90 mm | 1.78 mm | 11.32 | MLS | Cometic | C4623-070 |
| 90 mm | 1.78 mm | 11.32 | MLS | Cometic | C4624-070 |
| 90 mm | 1.78 mm | 11.32 | MLS | Cometic | C5860-070 |
| 90 mm | 1.78 mm | 11.32 | MLS | Cometic | C5861-070 |
| 90 mm | 1.91 mm | 12.15 | MLS | Cometic | C5860-075 |
| 90 mm | 1.91 mm | 12.15 | MLS | Cometic | C5861-075 |
| 90 mm | 2.03 mm | 12.91 | MLS | Cometic | C5860-080 |
| 90 mm | 2.03 mm | 12.91 | MLS | Cometic | C5861-080 |
| 90 mm | 2.13 mm | 13.55 | MLS | Cometic | C5860-084 |
| 90 mm | 2.13 mm | 13.55 | MLS | Cometic | C5861-084 |
| 90 mm | 2.18 mm | 13.87 | MLS | Cometic | C5860-086 |
| 90 mm | 2.18 mm | 13.87 | MLS | Cometic | C5861-086 |
| 90 mm | 2.34 mm | 14.89 | MLS | Cometic | C5860-092 |
| 90 mm | 2.34 mm | 14.89 | MLS | Cometic | C5861-092 |
| 90 mm | 2.49 mm | 15.84 | MLS | Cometic | C5860-098 |
| 90 mm | 2.49 mm | 15.84 | MLS | Cometic | C5861-098 |
| 90 mm | 3.05 mm | 19.40 | MLS | Cometic | C5860-120 |
| 90 mm | 3.05 mm | 19.40 | MLS | Cometic | C5861-120 |
| 90 mm | 3.56 mm | 22.65 | MLS | Cometic | C5860-140 |
| 90 mm | 3.56 mm | 22.65 | MLS | Cometic | C5861-140 |
The gasket volume is the empty space it leaves above each Subaru cylinder. It is added to the combustion chamber and reduces the compression ratio, the more so as it is large. Compare these values only between gaskets of the same bore.
| Fasteners | Engines | Tightening torque |
| Original cylinder head bolts | EZ30D | not published by the manufacturer |
Before fitting, check with a straight edge that the Subaru head and block faces are flat, and have any that need it resurfaced. Apply no gasket sealant: Cometic gaskets come already coated.
 | Athena O-Ring / Cut Ring A steel sheet coated with asbestos-free aramid fibre, with a stainless steel compression ring around each cylinder. The ring gathers the clamping load on a small diameter, where the seal is decided, while a silicone bead protects the water and oil passages. No other construction copes with pressures this high, and it is the only one suited to a head already fitted with a compression wire. |
 | MLS Cometic Stainless steel layers, stamped and joined by rivets. The outer layers carry active beads around each Subaru cylinder and each fluid passage. Moderate tightening is enough to seal and the bore distorts very little. This versatile construction ranges from the prepared naturally aspirated engine to moderate boost. |
Gasket bore. The Athena O-Ring comes in 90 mm (330166R on the right, 330167R on the left), the Cometic MLS in 90 mm (C5860, C4624 and H3570051S on the right; C5861, C4623 and H3027051S on the left).
Thickness. Subaru discloses no thickness for the original gasket of this engine. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.
| Your goal | Thickness to choose |
| Keep the original compression ratio | Original thickness unknown: measure the removed standard gasket and keep the offered value nearest to it |
| Skimmed cylinder head, make up the lost height | The offered value nearest to the removed standard gasket, plus the thickness removed when resurfacing |
| Forced induction build, lower the ratio | A thickness above the one measured on the removed standard gasket |
| Naturally aspirated build, raise the ratio | A thickness lower than the removed standard gasket, down to 0.69 mm, the lowest value in the range |
If you choose a thickness lower than the original, first measure with a dial gauge how far the pistons protrude above the Subaru block face: this figure gives the clearance that remains between piston and head.
 | Athena S.p.A. is an Italian maker of engine gaskets and components, with its head office and main plant in Alonte, in the Veneto region. It also produces in Spain, the United States, Brazil and India. Its multi-layer gaskets are fitted as original equipment by car manufacturers, and its entire racing range is designed and made in Italy. |
 | Cometic Gasket, Inc., a US company founded in 1989 in Concord, Ohio, designs engine gaskets and sealing solutions. Its reputation comes from the made-to-measure gasket, cut to the bore and thickness requested. All manufacturing remains in the United States, with American materials. |
| Criterion | Original gasket 11044AA603 and 10944AA003 | Reinforced gaskets |
| Construction | Construction not stated by the manufacturer | Multi-layer stainless steel, or steel and aramid fibre with a stainless ring |
| Gasket bore | not published | 90 mm |
| Thicknesses available | thickness not published by the manufacturer | 0.69 to 3.56 mm, 19 values |
| Compression ratio adjustment | None | Through the thickness chosen |
| Resistance to overpressure | Limited to standard output | Designed for forced induction |
| Brand | Model | Engine code | Power | Years |
| Subaru | OUTBACK (BH) 3.0 AWD | EZ30D | 219 hp | 2000-2003 |
| Subaru | OUTBACK (BP) 3.0 AWD | EZ30D | 219 hp | 2003-2004 |
OEM part number: 11044AA603 and 10944AA003
Important: the part numbers on this page match the Subaru EZ30D engine: read the engine code of your vehicle, then check the bore, before you order.
When the original gasket is no longer enough, the reinforced H6 gasket steps in: under higher combustion pressure it keeps its shape and is not crushed.
As soon as a turbo, a supercharger or a higher compression ratio comes into play, the Subaru head takes more load and the gasket becomes the most exposed part of the top end. A reinforced gasket stops gas or coolant leaks, and the head removal that would follow.
