Reinforced head gasket Porsche 3.8 M97.77

The Porsche engines covered

The M97.77 is the 3.8 litre flat-six of the Porsche 911 GT3 (997), and the M97.77R that of the 911 GT3 RS. Both engines are listed in the compatibility table below. Each bank of three cylinders has its own cylinder head and its own gasket, so the engine needs two.

The original gasket carries part number 997 104 170 8A. Porsche publishes neither its bore, nor its thickness, nor its construction. Sized for standard combustion pressure, it reaches its limit as soon as it rises: clamping load drops, the head lifts and coolant finds its way into a cylinder.

Reinforced cylinder head gaskets

Sealing also depends on the fasteners that press the heads onto the crankcase. A composite gasket is crushed for good beyond 100 N/mm²; the 301 stainless steel of an MLS gasket withstands 517 N/mm², 5 times more, and regains its shape at every combustion. Replace any head bolt that is stretched or marked.

This page presents part numbers H2457SPF027S and H2457SPF060S from Cometic, the American maker of racing gaskets, in a single construction: the multi-layer steel MLS. The bore is 102 mm for both; the thickness is 0.69 mm for the first and 1.52 mm for the second. Each part number is sold individually: plan on two gaskets per engine.

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: the thicker the gasket, the larger that volume. Here both part numbers have the same 102 mm bore; only the thickness changes, 0.69 mm or 1.52 mm.

Preparation and fitting

Before refitting the cylinder heads, lay a straight edge across each head and across the crankcase to check flatness, and have the faces ground if needed. Cometic gaskets arrive with their coating in place: do not apply any gasket sealant.

Technical guide

The construction offered

Cometic MLS A stack of stamped and riveted stainless steel sheets. The outer sheets carry active beads that surround every cylinder and every fluid passage. Moderate clamping is enough to seal and the bore stays stable: a versatile construction, from the tuned naturally aspirated engine to moderate boost. The part numbers H2457SPF027S and H2457SPF060S on this page are offered in this construction.

Choosing bore and thickness

Gasket bore. The Cometic MLS H2457SPF027S and H2457SPF060S come in 102 mm, in that bore only.

Thickness. No thickness is published for the original gasket 997 104 170 8A. 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 before choosing the 0.69 mm: this reading gives the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American manufacturer founded in 1989 in Concord, Ohio, producing engine gaskets and sealing solutions. Its reputation comes from the made-to-order gasket, built to the bore and thickness wanted and manufactured in the United States.

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 bore of the original gasket, which Porsche does not publish 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: 997 104 170 8A.

Important: the part numbers on this page only suit the M97.77 and M97.77R engines of the 911 GT3 (997): check the engine code of your Porsche before ordering.

Why switch to a reinforced gasket?

Once the standard gasket has run out of capacity, the reinforced one relieves it: facing higher combustion pressure, it holds its thickness instead of being squeezed flat.

On an engine pushed hard at high revs, on track or in a serious build, combustion pressure and thermal expansion test the head gasket before any other top-end part. A reinforced gasket prevents the leak, and with it the costly removal of two cylinder heads.