Thin pieces of metal, paper, and composite material are found at the intersection of your engine parts. They keep fluids from escaping, coolant out of the oil, and exhaust out of your engine bay. When you look at them, they seem simple enough, but the reality is that there is a lot more to it than you think. We partnered up with SCE Gaskets to show you some of the latest trends in gasket technology and get some tips for setting up your own application with the correct gaskets.
Unlike choosing the latest cylinder head design or changing to a new camshaft grind, it’s nearly impossible to “add” horsepower with a particular gasket or seal; rather the duty of gaskets is to be the gatekeeper of horsepower — to effectively corral the horses gathered by the engine builder. In racing engines, it is important to perform the task of sealing in the most efficient manner possible. Ryan Hunter, President of SCE Gaskets remarks, “There are a number of ways to accomplish this, one being to seal the engine with the least parasitic horsepower loss at the shaft seals.”
The Latest in Seals
SCE has had a chance to work with one of the leading seal designers to develop all-new front cover seals for Small Block Chevrolet, Big Block Chevrolet, and Chrysler applications. These seals are made of fluoroelastomer (more commonly known as Viton), a synthetic rubber that resists all fuels and oils, and has extremely high abrasion resistance for high-RPM use. Viton also has a high heat resistance with the ability to operate at temperatures exceeding 400 degrees. The seal contact area, or “lip”, is designed to reduce drag and still provide plenty of sealing for the high vacuum conditions common in current-technology racing engines.
Copper vs. Composite Head Gaskets
Traditionally, copper head gaskets were only used in the most extreme blown, nitrous or turbocharged engines. Copper is an ideal material for the task of cylinder head sealing due to the properties of the metal. Copper is malleable, elastic, and it’s a superior conductor of heat, making it very strong in comparison to composite gaskets. Though copper is a superior choice for combustion sealing, it has a bad reputation for fluid leaks. Back in the old days, you had to machine the cylinder head or block for installation of O-ring combustion seals, and use a combination of different kinds of goo to get a good fluid seal when using a copper gasket.
Modern-day technology has lead to the development of head gaskets that house an internal O-ring seal, such as the SCE ICS Titan. “The ICS Titan is a conventional, solid-copper body but with improvements to correct copper’s bad habits. The ICS Titan has built in fluid seals to cure the problem of coolant leaks, and Integral Combustion Seals so machining the block for O-rings is no longer required”, says Hunter.
While the ICS Titan head gaskets provide cylinder head sealing solutions for street-driven engines with power adders and racing engines with mid-level boost or nitrous, there is still a need to properly match the gaskets to the engine components. If you wanted to run the ICS Titans on an original 289 Mustang engine, this may not be a good idea. The decks and cylinder heads in the early 289 engines are prone to flex as the head bolts are tightened. Hunter says, “A composite head gasket would be able to compress near the head bolts and still provide adequate sealing at the mid-point between bolts, whereas a solid metal head gasket may not have been adequately clamped at the mid-point between head bolts and may experience coolant leaks.”
Composite head gaskets are made from flexible graphite foil mechanically clinched to thick, perforated carbon steel metal sheet. The graphite, high in carbon content, goes through chemical treatment, and provides the ability to maintain a seal despite shear loads between the head and deck thanks to the fact that it provides a certain degree of lubrication. Most composite gaskets have a rolled O-ring on each cylinder to seal them independently. For engines that experience expansion problems, more so on OEM or softer metals, the gasket will grow with heat and allow for a perfect seal.
Special Need in Head Gaskets for Mild to Wild Combinations
Performance and racing engines cover a wide array of component choices, from the warmed-over street engine with light nitrous to a nitro-fed billet Hemi with 60 pounds of boost.
High compression, naturally-aspirated racing engines and low- to mid-boost engines in anything from street use to mild racing can be assembled using a composite or copper head gasket. Typically, there isn’t a need for an O-ringed block or copper gasket at this performance level.
In the case of all-out racing engines with heavy doses of nitrous, high boost, blown alcohol or nitromethane, the combustion pressure becomes too much for the gasket body to hold without O-rings to “anchor” the gasket to the block and heads. If no O-rings were used, the pressure on the combustion seal would eventually balloon the head gaskets, ultimately resulting in a failure.
Ryan remarks, “The best method for sealing extremely high combustion pressure is the copper gasket/O-ring/receiver groove combination; this is the system currently used in all Top Fuel and Top Alcohol racing engines.” Circular O-ring grooves are machined around the combustion chambers in the cylinder head deck to a width which allows for a stainless wire to be tapped into the groove and held firmly in place. The depth of the groove is predetermined by the machinist to allow the O-rings to protrude to a specified height when bottomed in the grooves. The amount of protrusion will vary depending on the thickness of the head gasket and whether the engine will have receiver grooves in the block or not.
In a ‘standard’ copper gasket, the O-ring is what effects combustion sealing. Receiver grooves are required in only the most extreme racing engines and are most often machined in the cylinder block or in the case of an aluminum block, the cylinder sleeve. Positioning the O-rings in the head and receiver grooves in the block provides greater durability than the reverse due to the relative softness of the aluminum head. Ryan says, “Receiver grooves are placed on exactly the same centerline as the O-rings but machined wider than the O-ring wire and slightly shallower than the O-ring protrusion. The dimensional difference of the receiver groove to the O-ring allows the solid copper head gasket to be pushed or ‘extruded’ into the void of the receiver groove as the head bolts are tightened.” The result is that the head gasket is pressure-formed into a rectangular cross section within the receiver groove, which very effectively locks the head gasket in place and allows it to continue to seal even when the cylinder head is lifting from extreme pressure in the chamber.
Exhaust Gaskets – Another Sealing Challenge
Material choice is a large factor in both eliminating leaks and insuring the long-term durability of exhaust or header gaskets. The obvious advantage of metal gaskets is the inherent strength of the material; however, certain metals are too hard for use on anything but the smoothest of sealing surfaces. Multi-layer stainless steel exhaust gaskets are great for factory-finished surfaces on OEM components but not so much for aftermarket headers because the gasket material is too hard to deform and fill in leak paths. This is due to the reality that headers often leave a little to be desired in the areas of flange deflection and sealing surface finish.
Ryan suggests, “A better choice is either a compressible graphite gasket with a ‘fire ring’-style shield, or a malleable metal gasket such as an embossed copper exhaust gasket.” In both cases, the gaskets will deform to match any irregularities of the header flange and head surface for a tight, permanent seal. Because they put the exhaust gases to back to work, turbos will increase the pressure within the manifold. Due to this increased pressure, it is even more important to have an exhaust gasket with high tensile strength to prevent blowouts, but one that is able to conform to the mating surfaces as well, filling in voids and potential leaks paths.
Top 5 Ways to Ensure Good Cylinder Sealing, with Ryan Hunter
Number One – Flat surfaces, careful observation.
It almost goes without saying that the cylinder head and block sealing surfaces must be flat. An easy way to inspect for this is to place a straightedge on the sealing surface with a light behind it. Check any low spots with a feeler gauge; anything more than .002” requires re-surfacing.
It is also important to double-check a few items that are often taken for granted or overlooked entirely.
- Thread length – When using studs it is important to make sure that there are sufficient threads to allow the nut to tighten against the head/washer before bottoming out at the end of the threads.
- Dowel pin and ring dowel length – In cases where the cylinder head or block has been re-surfaced it is a good idea to insure that the counter bores or the dowel pin holes are still deep enough to allow the cylinder heads to set completely on the head gaskets and not on the dowels.
- Dowel pin leaks – “We have seen many cases in Small Block Chevrolet aftermarket heads where the dowel pin holes were drilled too deep and broke into the coolant passage of the head,” says Ryan. This will cause a leak at all four corners. If you find this to be the case simply plug the leak path with a little silicone before assembly.
Number Two – Metal-to-metal combustion seal.
All modern automotive power plants develop relatively high pressure in the combustion chamber; however, blown, turbocharged, or nitrous-assisted racing engines can build as much as three times the pressure of a stock engine. This kind of extreme pressure will literally blow any kind of sealant or elastomeric coating right off the combustion sealing area of the head gasket. When this occurs, a leak path is formed, often times leading right to a coolant passage, which pressurizes the radiator and pukes water on the track, causing the car to make a hard turn for the wall. The best combustion seal in extreme conditions is simply metal-to-metal with no coatings.
Number Three – Consider the chamber.
Often times the person assembling the engine fails to consider the size and shape of the combustion chamber when selecting the bore opening in the head gaskets. Many aftermarket cylinder heads have areas around the valves which extend beyond the cylinder bore of the block. If the gasket-to-chamber relationship is not considered, the fire ring of a composite gasket or the combustion seal could fall inside the combustion chamber while being outside of the cylinder bore. The way to check for this is simply lay the head gasket on the cylinder head in the installed position to insure that the fire ring or combustion seal is not inside the chamber at any point.
Number Four – Good fasteners, clean threads.
It is a very good practice to run a thread chaser through the threads in the block. In many cases the head bolt threads are wet and the thread chaser will remove any rust or thread sealant from the previous assembly. “Clean threads are essential to achieve proper clamp load, this is because any hindrance to the free rotation of the fastener in the threads will result in a lower compressive load on the head gasket”, Ryan says. This is because the torque wrench only measures the twisting force applied; it does not differentiate between the causes of resistance.
Gaskets require clamp load to seal, so good fasteners are always part of the conversation. Select a high quality set of fasteners with hardened washers which are designed for your engine. Bigger is not always better; similar to the example of the head gaskets matching the components, fasteners must also match the engine. Contact a reputable manufacturer who specializes in fasteners rather than one who says, “we also sell bolts”.
Number Four – Re-torque.
This extremely wise practice has fallen out of favor, mostly because gasket manufacturers have been hesitant to recommend it for fear of lost sales to another brand that does not. The truth is, racing engines will always benefit from being re-torqued regardless of the style head gasket being used. While it is true that some gaskets are more compressible than others as mentioned above, it is also true that the block and heads will expand with heat. Ryan states, “This means that the fasteners will have a higher tensile load and the gaskets will have higher compressive load when the engine is at operating temperature than when it is cold. In the case of composite gaskets this increased load results in what the gasket industry calls ‘creep relaxation’ which is another way of saying that the gaskets compress over time.” In the case of a solid metal gasket there is technically zero compression; however, there is still seating that occurs in the threads and whatever sealant or coating there may be on the gasket body. The idea behind the re-torque practice is to restore the proper tension to the fasteners after the engine has completed the first heat cycle, which is up to running temperature and then back to cold.
The process is simple; after the engine has returned to room temperature, retrace the torque sequence one fastener at a time by loosening the nut or bolt slightly to relieve friction set (the familiar “snap”) and then pull the fastener back to the recommended torque value. It can be a hassle in some cases, but who wants to lose a head gasket while in the lead? Doing a re-torque is worth the hassle.
Our Lips are Sealed
Regardless if you have a 200 or 2,000 horsepower engine, everybody wants a properly sealed engine. In the larger spectrum, the amount of money you have to invest into the correct gaskets is a fraction of what it costs to build a premium engine. Hopefully you can take some of the information from our article when it comes to building your next engine.