Reinforced cylinder head gasket Opel 20E and 20S

The Opel engines covered

The Opel 20E and 20S petrol engines, of 2.0 litres, are fitted to the Opel Manta B, Rekord E and their variants listed below.

The original gasket part numbers for these engines are 6 07 971, 90 323 445 and 90 349 947. Opel publishes neither the bore, nor the construction, nor the thickness. Each engine takes a single one. It is sized for standard combustion pressure: when that pressure climbs, the clamping load gives way, the cylinder head lifts and coolant gets into a cylinder.

Reinforced cylinder head gaskets

The head gasket does not seal by itself: the fasteners that clamp the head to the block contribute just as much. Above 100 N/mm², a composite gasket settles with no recovery; the 301 stainless steel of MLS gaskets holds up to 517 N/mm², 5 times more, and springs back with every combustion.

This page gathers the part numbers of Cometic, an American maker of racing gaskets, for a single construction: the multi-layer steel MLS. Every gasket has a 97 mm bore and 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, one gasket per engine.

Technical specifications

The gasket's volume is the space it provides above each cylinder. It comes on top of the combustion chamber and reduces the compression ratio, the more so the larger the volume. Only compare these values between gaskets of one bore.

Preparation and fitting

Before assembly, check with a straight edge that the head and block faces are flat, and have them resurfaced if needed. Add no sealing paste: Cometic gaskets are supplied coated.

Technical guide

The construction offered

MLS Cometic Stainless steel layers stamped and riveted together. The outer layers have active beads around each cylinder and each fluid passage. A moderate tightening torque is enough to seal, and the bore barely distorts. This versatile solution suits anything from the prepared naturally aspirated engine to moderate boost.

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in 97 mm (C4512), in that bore alone.

Thickness. Opel does not state the thickness of the original gasket. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

With a thickness smaller than the original, measure with a dial gauge by how much the pistons protrude above the block face: this value gives the clearance remaining between piston and head.

The brand

Cometic Gasket, Inc., founded in 1989 in Concord, Ohio, is an American maker of gaskets and sealing solutions for engines. It has specialised in the made-to-measure gasket, cut to the bore and thickness requested. Its output stays entirely in the United States, using 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 the manufacturer does not state 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: 6 07 971, 90 323 445 and 90 349 947.

Important: the part numbers on this page fit only the 20E and 20S engines: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket is at the end of its tether, the reinforced gasket takes over: subjected to higher combustion pressure, it keeps its shape and is not crushed.

Turbo, supercharger or a raised compression ratio: the head gasket is the first to take the strain, the most stressed part of the top end. A reinforced gasket prevents the leak and the costly head removal that follows, with the car left off the road.