Michael Galimi
May 5, 2010
Photos By: Steve Baur

It's common knowledge that head gaskets are a necessary evil in our world of internal combustion. "The purpose of a head gasket is to seal the cylinder head and engine block," explains Kevyn Kistner of Cometic Gaskets. And while sealing the head to the block seems like a simple task, the amount of stress, and the environment those gaskets live in, is as harsh as it gets in the internal combustion process.

That thin gasket is an extremely important piece whether you're talking in terms of horsepower or reliability.

Ron Rotunno of Fel-Pro also added, "From a sealing perspective, they [head gaskets] have the toughest job in the engine, as they must seal hot combustion gases, oil (pressure and drain back), as well as coolant-all the while making positive contact between a dynamic head and block assembly. This is not a static assembly-the head lifts as each cylinder fires and also exhibits scrubbing (east-west movement), for which the head gasket must accommodate." Technological advancements have helped produce stronger and better head gaskets for today's high-performance engines though.

Mike Dezotell of Dez Racing said it best when he pointed to street-driven Stangs in his shop that are approaching 1,000 hp. "Better head gasket technology has allowed us to put serious boost into these engines without fear of blowing the head gaskets. Boost and cylinder pressures are much higher than what we saw 10 years ago," he said.

To get you up to speed, let's start with the basics. There are four styles of head gaskets in the marketplace: MLS (multi-layer steel), composite, copper, and elastomeric. In the Mustang world, composite and MLS gaskets are the most commonly used. Copper head gaskets are quite popular in high-end, low-production, racing engines.

"Modular Ford, or any OHC-style engine, should always use an MLS gasket (naturally aspirated or power adder) to maintain cam-bore centerline and minimize line-bore distortion," explained Brian Carruth of Trick Flow Specialties. This is due to the sensitive nature of the camshaft location in the heads. If thicker or thinner gaskets are used, the cam timing will be altered. MLS gaskets are not actually required for modular applications, but the Trick Flow guys do recommend them. On the 5.0L side, Mike Dezotell said both graphite and MLS work, but leans towards the MLS for superior sealing. Some precautions need to be taken when utilizing this style gasket though, as they require extremely smooth block deck and head surfaces for a proper seal.

Graphite head gaskets are popular, but are deemed for one-time use. A switch to graphite gaskets is suggested when swapping cylinder heads, especially if you convert to aluminum heads. Since iron and aluminum have different expansion rates, graphite head gaskets can draw heat away from hot spots and help keep the heads and block sealed under adverse conditions.

"The key difference between traditional passenger car head gaskets and Fel-Pro Wire Ring-style performance head gaskets is the wire-ring combustion seal. It is inserted within a 321-series stainless steel armor surrounding each cylinder, and the wire-ring design provides highly concentrated sealing around the combustion chambers. The pre-flattened wire-ring raises combustion sealing force to roughly three times that of standard head gaskets. These gaskets are available with either copper (for early aluminum head applications) or steel (all others) wire-rings," shared Rotunno.

As horsepower is increased, better seal is required. Carruth said it best: "Everything has a limit, and if you stress something beyond the material's properties it will fail." The same can be said for graphite gaskets when the cylinder pressure increases due to the use of nitrous or forced induction. There isn't a given power range when graphite gaskets will fail, but most people should consider stepping up to an O-ring or MLS gasket when they add a power adder, especially in 5.0L applications when the heads, cam, and intake have been upgraded.