Reinforced head gasket Ferrari F105A F105AB 308 Mondial

The Ferrari engines covered

The F105A and F105AB are Ferrari V8 petrol engines. They power the Ferrari 308 GTB, 308 GTS, Mondial and Targa 308 GTS models listed in the compatibility table below.

The original gasket carries part number 168.946. Ferrari publishes neither its bore, nor its thickness, nor its construction. The engine takes two cylinder head gaskets, one per bank of cylinders, sized for the standard combustion pressure; when that pressure climbs, the clamping force eases, the head lifts slightly and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

Sealing does not rest on the gasket alone but also on the fasteners that press the head onto the block. Beyond 100 N/mm², a composite gasket compresses for good; the 301 stainless steel of MLS gaskets takes 517 N/mm², 5 times more, and recovers its shape at every combustion. Also check the condition of the head bolts and replace any that are stretched or damaged. Do this for the bolts of both cylinder heads.

This page brings together 3 Cometic part numbers, from the American maker of competition gaskets, for a single construction: MLS, multi-layer steel. Two bores are offered: 83 mm (C4428-045 and C4428-060) and 89 mm (C4429-045). The 83 mm bore comes in 1.14 mm and 1.52 mm; the 89 mm bore comes in 1.14 mm only. The engine takes two gaskets, one per bank of cylinders: order the quantity needed for both banks. The thicknesses offered let you 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 only gaskets of the same bore: 83 or 89 mm here.

Preparation and fitting

Before reassembly, check the flatness of the head and block mating faces with a straightedge and have them resurfaced if needed. Cometic gaskets arrive already coated: do not apply any sealing paste. Also clean the gasket faces thoroughly before fitting. Do this on both cylinder heads.

Technical guide

The construction offered

Cometic MLS Several stainless steel sheets, stamped and riveted together. Each outer sheet carries active beads tracing the outline of every cylinder and fluid passage. A moderate clamping load is enough to seal, and the bore distorts very little. This versatile gasket suits anything from a tuned naturally aspirated engine to light boost. All the part numbers on this page are offered in this construction. Here it serves both banks of the Ferrari V8.

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in 83 mm (C4428-045 and C4428-060) and 89 mm (C4429-045).

Thickness. No thickness is published for the original gasket 168.946. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

To choose a thickness below the original, first use a dial gauge to read how far the pistons stand above the block face: that figure gives the clearance left between piston and head. On this V8, take that measurement on each bank of cylinders.

The brand

Cometic Gasket, Inc. is an American company founded in 1989 and based in Concord, Ohio, which designs and builds gaskets and sealing parts for engines. It earned its name with made-to-measure gaskets, cut to the bore and thickness required, all made in the United States from American materials. Its part numbers for these Ferrari engines are offered here in two bores.

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 83 and 89 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: 168.946.

Important: the part numbers on this page suit only the F105A and F105AB engines: check your Ferrari's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket is no longer enough, the reinforced gasket replaces it: under higher combustion pressure it keeps its shape instead of collapsing. For the Ferrari models on this page, it is the answer as soon as the engine goes beyond its original output.

Whether you add a turbo, raise the compression ratio or rev higher with livelier cams, the cylinder head gasket becomes the weak link of a high-output engine. A reinforced gasket prevents the leak and the head removal that goes with it, far costlier than the gasket. On these Ferrari engines, the reinforced gasket is the first item to address once you go beyond the original output.