In today’s enthusiast marketplace, boost equals power. Boost has always been an easy path to ultimate high performance. It was just a little bit more black magic years ago to properly tune a boosted engine than it is today. Having the correct technical knowledge is key to making the most reliable power with boost. Because whether you’re boosting your street car, or trying to blow your heads off at the track, boost is king! But boost–big or small–must be contained within the engine in order to improve performance, and it’s companies like SCE Gaskets who make this possible through the use of their time-tested head gaskets.

While a lot of races are won using boost, lack of control is a big reason that a lot of races are lost because of boost. Blown head gaskets. Blown intake gaskets. Blown hoses and clamps. Even stretched or broken cylinder head fasteners can all lead to boost losses and lost races. But we know there are people out there running double- and even triple-digit boost figures in their engines, so how are they keeping it all in?

Copper head gaskets offered by companies like SCE give the end-user the ability to seal up forced induction pressures with ease.

Cylinder Pressure Limitations

Whether you’re racing down the quarter-mile, or sitting behind the wheel of a big-rig for a long haul, the head gaskets sealing your cylinders were designed to function within specific operating environments only. If you’re boosted, then the higher combustion pressures in your cylinders dictate the use of higher-strength materials and better construction than run-of-the-mill OE gaskets. Boosting an engine effectively raises its final compression ratio, which is the engine’s static compression ratio plus the extra boost factored in. So that means that your boosted engine will require head gaskets with sealing capabilities of a high compression race engine, even if you’re running low compression on the street.

The formula I use to calculate what I like to refer to as the “Final Compression Ratio” or FCR is:

((Boost / 14.7) + 1) x Static Compression = FCR

Let’s say you have an engine with 9.0:1 static compression ratio, and you run 8 psi boost, your FCR will be 13.9:1.

((8/14.7) + 1) = 1.544
1.544 x 9.0 = 13.9

These two graphics show the specifics of wire ring installation to ensure maximum performance achievement.

Conformability Is Key

Steel is stronger than copper, but copper is much more conformable than steel.

I once visited with a guy who was dropping off his block and heads at a machine shop yet again, for what seemed like the hundredth-time. He said he keeps blowing head gaskets and he’s even tried the very best MLS (multi-layer steel) gaskets money could buy. I mentioned copper gaskets. He replied that he never tried copper because he reasoned that steel is stronger than copper. And while he may be technically correct–steel is stronger than copper–but when making extreme performance head gaskets that will last, it is not just about the strength of the material. It’s more about the conformability of it. And copper is much more conformable than steel.

Here’s a shot of properly-installed O-rings pressed into a set of Dart Pro 1 heads for a 2,500 horsepower engine.

In order to stay sealed under the highest cylinder pressures, you need a material that can conform to the impurities of the sealing surfaces. Especially when the gaskets start to get heated up and pushed around. Composite gaskets can do a pretty good job of conforming, but they’re not very strong. Copper is much stronger than any composite gasket material, yet it’s still malleable, meaning copper can stretch and conform to remain sealed. Kind of like “give a little, take a lot.” Copper might even sacrifice itself to the mighty boost gods every now and then, but it’ll hold up much longer than its composite counterparts. And it’ll get you home, or into the winner’s circle safely.

This is the aluminum block with the correctly-machined receiver grooves cut into the steel cylinder liners.

SCE has compiled a series of charts outlining the baseline limitations for each type of head gasket used in normally aspirated, supercharged (aka boosted), and nitrous oxide-injected engines. These are only guidelines, as actual engine parts and combinations (FCR, camshaft specs, type of fuel used, etc.) will always have an impact on ultimate combustion pressures.

Notice how in the boosted and N2O charts MLS gasket performance degrades much quicker than copper.

Pressure Conversions

Choosing the right head gaskets and properly tuning a boosted engine requires just a bit more than the most basic understanding of pressure. But pressure is measured, and/or represented, in all sorts of different ways around the world. Even on my own dyno I sometimes have trouble converting boost numbers into a format my brain is accustomed to seeing, which has always been Pounds-per-Square-Inch (PSI) for me. But boosted PSI inside an engine is more accurately represented as PSIG, (aka Gauge Pressure, see chart), when tuning. And gauge pressure is different from PSIA, which is “Absolute” or “Actual” pressure. PSIA is boost + atmospheric pressure. And since atmospheric pressure can change from run-to-run, and from day-to-day, it’s important to know that it will affect the true, overall PSI your engine will see inside its runners.

Here’s a chart I made up to help converting all the ways I have seen an engine’s boost measured. There may be more ways that I’m unaware of, so please feel free to let me know if I’m missing any. I also threw vacuum (inHg) into the chart, and I use this pretty regularly when tuning different engines and EFI systems on my dyno since no two system’s software may use the same values. One EFI tuning software might show kPa. One might use PSIA. One could show BAR. I have to be able to know what’s what when tuning these damn things and it can get confusing sometime. So here’s my chart. Also, feel free to let me know if I’ve made any errors. I’m not a math or scientific wiz. I just fed all this data I found on the internet into my Excel spread sheet and it spit out this chart. So it must be true. Right?

KEY:

• PSI = kPa × 0.145037738
• inHg = kPa x 0.2952998751
• BAR = kPa x 0.01
• PSIG = PSIA – 14.7
• PSIG = Pressure Gauge (Boost inside the engine as seen on a typical gauge)
• PSIA = Pressure Absolute (Boost + Atmospheric Pressure)

While it’s also possible to install the O-rings in the block, and cut receiver grooves into the heads. This method is not ideal when running aluminum heads due to the deformation of the grooves in the softer aluminum.

Below is a list of the three types of copper head gaskets manufactured by SCE; each one is optimized for a different usage scenario. For the best recommendation for your particular engine, contact SCE directly.

Pro Copper (P prefix part numbers)

• Solid copper construction, pre heat-treated.
• Requires additional sealant for coolant (if liquid cooled) and oil passages.
• Requires O-rings and receiver grooves for best combustion sealing.
• Applications: Top Fuel, Blown Alcohol, Nitrous, and all Boosted Gas race engines with O-rings (and receiver grooves) in block or heads.

SCE Titan (T Prefix part numbers)

• Solid copper construction with coolant and oil seals, pre heat-treated.
• No additional sealant required for coolant and oil passages.
• Requires O-rings and receiver grooves for best combustion sealing.
• Applications: Boosted, Nitrous applications in racing or street driven engines which require dependable coolant sealing with O-rings (and receiver grooves) in block or heads.

ICS Titan (S Prefix part numbers)

• Heat-treated copper body with coolant, oil and combustion seals built in.
• No additional sealant required for coolant and oil passages.
• No O-rings required for combustion sealing.
• Applications: Turbocharged, Blown, Nitrous applications in racing or street driven engines which require dependable coolant sealing and superior combustion sealing without O-rings or receiver grooves in block or heads.

To keep from lifting the cylinder heads, high-boost or N2O race engines are often built with larger diameter cylinder head studs. If you’re planning to O-ring an engine fitted with larger head studs, you must consider the copper gasket’s clamping area too. See the photo and caption below for more details.

SCE’s Ryan Hunter walked us through these tips for successfully running copper head gaskets.

What’s the best way to prepare the block and cylinder head? Use a residue-free solvent such as aerosol brake cleaner and a clean rag on the head and block sealing surfaces before assembly. Of course the block and head should be flat within .002-inch across and .004-inch lengthwise, with surface finish of 60 to 80RA preferred, 60 to 100RA acceptable.

Multi-Layered-Steel, (MLS), head gaskets are sealing most factory engines today. And they can seal boosted engines too. But their performance degrades faster than copper when subjected to extremely high boost or N2O levels.

What about re-torquing? Solid copper does not compress, it displaces. Since the copper gasket body does not compress no re-torque is technically necessary. However, since an engine built using a copper head gasket is almost always within the realm of extreme performance, SCE recommends a re-torque after a complete heat cycle.

What are some of the specifics of O-ring sealing? Head gasket sealing is a matter of balance and more pressure is needed around the combustion seal than other areas of the gasket. This is due to the vast difference in pressures acting against the head gasket. Consider that an engine developing 1.5 to 2 horsepower per cubic inch will have combustion chamber pressures well over 1,000-psi. While, less than one half-inch away, the cooling system is just running at only 15-22psi max. Since a standard copper gasket is flat, clamp load from the head bolts will be distributed evenly unless some method is used to ‘tip the balance’ and concentrate more load around the combustion sealing area. The accepted method has been to install O-rings on one component, and receiver grooves in its mating part, to accept the O-ring.

Here’s a good tip for installing all types of head gaskets on engines running head studs. Put the gaskets on the block first. Then screw in the fasteners. Trying to get head gaskets down over head studs is a very quick path to ruined gaskets and frayed nerves.

In Conclusion

When you’re building an engine with a large amount of boost — whether the pressure comes from a supercharger or a turbocharger — having a head gasket which seals that boost into the engine is a critical step of the build process. There are many factors which come into play, and perhaps the most important is selecting the correct product for the application.

### Article Sources

#### Michael Petralia

Mike is a veteran from Weiand Automotive Industries, where he spent 9 years testing & developing many products. He later moved to the editorial trade, holding titles at several high performance magazines. In 2006, Horsepower TV's Tech Producer position moved him to Tennessee where he later opened Hardcore Horsepower, LLC, building cars and engines for magazines and customers alike. Mike's shop has a 2,000hp engine dyno, a 1,200cfm flowbench, and a 1,250hp chassis dyno giving him unparallelled testing & tuning capabilities.

### Horsepower delivered to your inbox.

Build your own custom newsletter with the content you love from EngineLabs, directly to your inbox, absolutely FREE!