Reinforced head gasket Toyota Lexus PH11

The Toyota engines covered

The Lexus and Toyota PH11 racing V8 takes two cylinder head gaskets, one per cylinder bank. It powers no production vehicle: it is reserved for competition.

The manufacturer says nothing about the original gasket of this engine: no part number, no bore, no construction and no thickness. A racing engine runs at combustion pressures far above those of a production engine, and the gasket is the first to suffer: the clamping load relaxes, the head opens up and coolant makes its way into a cylinder.

Reinforced cylinder head gaskets

Sealing does not rest on the gasket alone: the studs and nuts that clamp each head onto the block account for half of it. The stainless steel of an MLX gasket holds its clamping load under high pressure and does not settle over time.

This page offers sixteen part numbers from the American maker Cometic, a specialist in racing gaskets, in one construction only: MLX. Their bore is 106.68 mm and their thicknesses range from 0.81 to 1.32 mm. The V8 takes one gasket per cylinder bank: the C5584 part numbers are for the left bank, the C5583 part numbers for the right bank.

Technical specifications

A gasket's volume is the space it leaves free above each cylinder: it adds to that of the combustion chamber and lowers the compression ratio. Only gaskets of the same bore can be compared.

Preparation and fitting

Before fitting, check the flatness of both heads and of the block with a straight edge, and have any warped surface machined. Every Cometic MLX gasket is inspected before it leaves the factory.

Technical guide

The construction offered

Cometic MLX Several stamped, riveted stainless steel sheets, the centre one folded into a stopper around each combustion chamber, under a heat-resistant coating. The clamping load concentrates at that point without distorting the bore any further. It is the strongest of the all-steel constructions, suited to heavily stressed engines, here in 106.68 mm.

Choosing bore and thickness

Gasket bore. The Cometic MLX gasket is offered in 106.68 mm (C5584 and C5583 series), with no other bore.

Thickness. The manufacturer publishes no thickness for the original gasket of this engine: the dimension of the removed gasket is the reference. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

As no original thickness is published, use a dial gauge to read how far the pistons stand proud of the block's gasket face before choosing the thickness: this figure gives the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American company based in Concord, Ohio, founded in 1989, that designs gaskets and sealing solutions for engines. It became known for the made-to-measure gasket, cut to the bore and thickness requested and made entirely in the United States from American raw 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 106.68 mm bore of the gaskets offered 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: not published by the manufacturer.

Important: the part numbers on this page suit the Lexus and Toyota PH11 racing V8: each engine needs two gaskets, one per cylinder bank. Order one C5584 part number for the left bank and one C5583 part number for the right bank.

Why switch to a reinforced gasket?

When the original gasket is no longer enough, the MLX gasket carries on: under high combustion pressure it keeps its shape and does not crush.

On a racing engine, where combustion pressure keeps climbing, the head gasket is the part that gives way first. The reinforced gasket prevents the leak, whereas removing both heads of a V8, long and painstaking work, costs far more than the gasket.