Reinforced head gasket Porsche Cayenne M48.00 M48.50 V8 4.5L

The Porsche engines covered

The V8 of 4.5 litres, the Porsche M48.00 and M48.50, powers the Porsche Cayenne S and Cayenne Turbo (9PA), in the version detailed below; the Cometic part numbers on this page are announced by the maker for the M48.00 and M48.50.

Porsche gives the part number 948.104.171.06, 948.104.172.05 for the original gasket of this engine, but publishes neither its bore, nor its thickness, nor its construction. Each bank of four cylinders has its own head and gasket, sized for the standard pressure: as it climbs, the clamping load fades, the head lifts off the block and coolant passes into a cylinder.

Reinforced cylinder head gaskets

The head gasket does not seal on its own: the fasteners that press the Porsche head onto the block count as much as it does. Above 100 N/mm², a composite gasket settles for good; the 301 stainless steel of MLS gaskets withstands up to 517 N/mm², 5 times more, and recovers its shape at every combustion.

This page gathers the part numbers of Cometic, an American maker of competition gaskets, under a single construction: MLS, a multi-layer steel design. The V8 needs two different gaskets, one per bank, and each bank comes in several bores. They come in bores of 93 and 95 mm, and in thicknesses 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

The gasket volume is the empty space it leaves above each Porsche 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.

Preparation and fitting

Before fitting, check with a straight edge that the Porsche head and block faces are flat, and have any that need it resurfaced. Apply no gasket sealant: Cometic gaskets come already coated.

Technical guide

The construction offered

MLS Cometic Stainless steel layers, stamped and joined by rivets. The outer layers carry active beads around each Porsche 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.

Choosing bore and thickness

Gasket bore. Cometic MLS comes in 93 mm (H2796SP3051S on the left, H2797SP3051S on the right) and in 95 mm (C4535 on the left, C4536 on the right).

Thickness. Porsche 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.

If you choose a thickness lower than the original, first measure with a dial gauge how far the pistons protrude above the Porsche block face: this figure gives the clearance that remains between piston and head.

The brand

Founded in 1989 in Concord, Ohio, Cometic Gasket, Inc. is a US company that designs engine gaskets and sealing solutions. Its name was made by the made-to-measure gasket, cut to the bore and thickness you ask for. All manufacturing remains in the United States, with American 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 bore of the original gasket, which Porsche does not disclose 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: 948.104.171.06, 948.104.172.05

Important: the part numbers on this page match the Porsche M48.00 and M48.50 engine: read the engine code of your vehicle, then check the bore, before you order.

Why switch to a reinforced gasket?

Once the standard gasket reaches its limit, the reinforced V8 gasket takes over: facing higher combustion pressure, it holds its shape and resists crushing.

As soon as a turbo, a supercharger or a higher compression ratio comes into play, the Porsche 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.