Michael Galimi
May 5, 2010
Photos By: Steve Baur

The O-ring head gaskets incorporate a special wire around the cylinder bore openings of the gasket, and the cylinder head must have an O-ring receiver groove machined in. As the head is torqued, the O-ring is pressed into the receiver groove, forming a stronger seal. When it comes to O-ring-style gaskets, Fel-Pro is a popular brand.

"The Fel-Pro Loc-Wire Performance gaskets work on a similar concept as the Wire Ring Performance gaskets using an oversize wire-ring, which requires a matching receiver groove. This design uses both clamp load as well as the mechanical gasket/wire/deck interface to maintain sealing integrity," said Rotunno.

The latest craze is to use MLS gaskets. "The head surface and block deck have to be perfectly straight and smooth to use MLS gaskets. I use a graphite gasket on stock 5.0L blocks because the deck's RA [RA stands for roughness average and is measured using a profile-meter] is usually too rough for MLS gaskets," commented Dezotell. Cometic recommends a minimum RA of 50 micro-inches for use with MLS gaskets, anything rougher will affect the sealing properties. According to Dezotell, the RA of a stock 5.0L block, despite it being too rough for MLS applications, is just right for the graphite ones.

MLS gasket technology is truly remarkable. Carruth stated, "Because of different materials and the thermal expansion rates, a cylinder head gasket must move and adjust with the block/heads to maintain a seal. A MLS gasket kind of works like a spring."

MLS gaskets often utilize between three and seven layers of steel with the outer layer/layers made from stainless spring steel. The outer layer is also coated with a thin rubber coating. The center layers can vary in thickness and provide the support and seal. Another positive is that they can be reused over and over.

Serious engines with high compression, big nitrous oxide hits, and massive boost will be best suited to the use of copper head gaskets or Cometic Phuzion MLS gaskets. Copper head gaskets are found in the NHRA Nitro ranks, proving durable under the harshest conditions. Ken Sink of Milodon said, "I recommend running copper gaskets on all high-compression and supercharged/turbocharged applications."

The copper gaskets are built using a solid piece of copper and a CNC machine. Milodon says they are acceptable for street use as well. Sink recommends good machine work (Ed. note: on the block and heads to ensure a flat and smooth surface) and a dab of silicone on each side of the gasket around the water ports to help seal them.

Sink made the suggestion to add stainless steel 0.030-inch O-rings in the block, which would require a machine shop to add O-ring receiver-grooves around each bore. The O-ring acts in a similar fashion to the graphite O-ring head gaskets by forming an extra strong seal. Copper head gaskets receive the same torque sequence and final torque settings as composite or MLS gaskets.

Bolt 'em Down
We'd be remiss if we didn't discuss head bolts and/or studs when talking about head gaskets. Having proper head fasteners are an integral part of head gasket sealing and they are available from several companies like ARP, Milodon, Mr. Gasket, Manley, Ford OEM, and others. Essentially, there are three kinds of head fasteners when dealing with Ford engines-torque-to-yield bolts, head studs, and regular head bolts.

For modular engines, most people rely on OEM Ford replacement bolts that are torque-to-yield, or they use traditional head studs. "Bolt stretch will occur when a bolt is installed properly. Torque-to-yield bolts require a specific installation process to properly stretch the bolt according to the manufacturer's recommendations. This ensures that the proper clamp load is being achieved. It usually consists of tightening each bolt to a specific setting, and then turning each head bolt another 90 degrees; then you follow up with another 90-degree turn. These bolts are for one-time use. The stock 5.0L head bolts have the same result-once removed, they must be discarded.

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