One of the basic tenants of hot-rodding is finding ways to add more power. One popular way of doing that is by adding displacement. To do that there are two dimensions in an engine’s configuration which determine displacement: the engine’s bore and stroke.

At the risk of stating the obvious, the bore of the engine is the diameter of the cylinder (and the piston inside of it), while the stroke is the vertical distance the piston travels within the cylinder. There are lots of debates, both in real life and on the internet, about which dimension is worth more power.

Enter Jason Fenske of Engineering Explained. With his desire to explain how pretty much anything and everything automotive works, he’s taken on the subject. “If your goal is to create as much horsepower as possible, there are reasons why it is advantageous to go with a larger bore, relative to the length of stroke,” Fenske starts out. However, if your goal is to create an engine that is as efficient as possible, there are reasons to go with a longer stroke relative to the bore.”

In order to fully illustrate the differences, he has come up with some rather extreme examples on either end of the spectrum (more than boring a factory engine .040-inch over, or adding 0.5-inch of stroke).

“For the purposes of this discussion, we’ll discuss three cylinders all with the exact same displacement. All will have a half-liter displacement, and the middle of the road example will be square at 86mm (3.386 in.) bore and 86mm stroke. The 0.5-liter square cylinder is one that you will find in many roadgoing engines, especially 2.0-liter I4s and 3.0-liter V6s,” says Fenske

For the oversquare (bore larger than the stroke) engine example, Fenske has created a 117mm (4.606 in.) bore, 47mm (1.850 in.) stroke cylinder. “That puts the bore-to-stroke ratio similar to an F1 engine,” Fenske explains. “Typically, F1 cylinders wouldn’t be this large, but these dimensions keep the cylinders equal displacement for the example.”

For the undersquare (stroke larger than the bore), another cylinder of exaggerated dimensions was created, with a 63mm (2.480 in.) bore and 158mm (6.220 in.) stroke. This cylinder has a reverse bore-to-stroke ratio from that of an F1 engine,” says Fenske. “A 63mm bore with a 158mm stroke is far from anything you’d typically in a roadgoing car, but it will help illustrate the points.”

Making Horsepower

One thing to remember about horsepower, especially when chasing it, is that it is a calculated unit, and is essentially torque over time. “One of the critical things about horsepower is, how fast can you rev your engine,” says Fenske. “It is a function of torque multiplied by RPM, multiplied by 5,252 (assuming English units). If torque is held constant — which isn’t easy to do — horsepower is simply a function of RPM. If you can rev your engine higher, you can make more power, and that’s the ultimate goal.”

There are a lot of factors that determine maximum engine speed, but for the purposes of this hypothetical discussion, Fenske chooses to use piston speed as the ultimate limiting factor of potential hypothetical engine speed.

“By decreasing your stroke length, you’re able to increase your RPM limit. Automotive engines don’t typically exceed 25 meters-per-second. Once you exceed that limit, you start to run into issues. We can calculate average piston speed for the different examples fairly easily using the following equation:”

“If we know the piston speed, we can plug that in and then do some dividing and figure out maximum RPM based on stroke length,” explains Fenske. “For the oversquare cylinder, we get a maximum RPM of 16,000. For the square cylinder, it’s about 8,700 rpm, and for our undersquare cylinder, our limit is going to be about 4,700 rpm. Because the shorter stroke configuration can rev higher, it has more power strokes per second, and therefore makes more power.”

Fenske notes, that just because the engine configuration can rev to 8,700rpm without overspeeding the piston, doesn’t mean the engine will rev that high. There are other limiting factors besides piston speed.

The second advantage of a big-bore setup is its physically-larger size. “This has to do with the size of your valves and how much airflow we can get through the engine,” says Fenske. By being able to fit physically larger valves, you are able to move more air into and out of the cylinder.

“Starting with an example of an 80mm-bore engine, we’ll say it has two 30mm intake valves and two 25mm exhaust valves. Using that example, we’ll scale it to our cylinder examples,” Fenske postulates.

“After scaling, the largest cylinder has two 44mm intake valves versus 24mm intake valves on the small-bore example, and the exhaust valves are 37mm on the large bore example, and 20mm on the smallest. Now, giving these exhaust valves the exact same amount of lift (5mm), the intake valve area of the largest example is about 25.2 square centimeters; he 86mm example is 18.6 sq-cm, and the 63mm bore, you get about 13.7 sq-cm.”

Obviously, being able to move almost twice the amount of air is an advantage for the larger bore in this example, but in practical applications, the difference between “small bore” and “big bore” is far less drastic. However, Fenske does bring up a good point in the video about the large valves and reduced volumetric efficiency at low-RPM, but that’s a rabbit hole for another day.

• 
• 

In addition to having a shorter stroke length and the associated theoretical higher RPM limit, the larger bore allows for larger valves to fit in the cylinder head, which in turn increased the engines maximum airflow potential.

Creating Efficiency

Sometimes, all-out horsepower isn’t the goal, and the goal is to have an efficient all-around performing engine, for say a street car. According to the general logic of mechanical engineering, the longer stroke provides that efficiency over a bigger bore.

“One of the reasons I’ve often heard for why long stroke engines are more efficient, is that the amount of surface area they have, relative to the volume inside of the cylinder I low, meaning there is less overall area to reject heat to, during combustion. That means more of that heat is turned into useful work pushing the piston down,” says Fenske.

“Calculating the surface area for our examples is easy enough, and we find that the oversquare engine has a surface area of 386 sq-cm, the square engine has a surface area of 349 sq-cm, and the long-stroke has a surface area of 378 sq-cm. So we see that as you move either direction away from a square engine design, you start to get more surface area.”

Those numbers may seem to not support the idea that the longer stroke is more efficient. However, Fenske points out the flaw in using the total swept area of the cylinder. “You have to factor in compression ratio and what the cylinder looks like at the time of combustion,” he explains.

“The undersquare cylinder is actually the closest to square (at the time of combustion) in this example. Running the numbers at the point of combustion, you see that the long-stroke cylinder has the least amount of surface area, and is now turning the most heat from combustion into usable work.”

Tied into that is also burn duration, which, we’ll warn you, gets complex. “The logic here is that the quicker you can burn the air-fuel mixture, the more efficient of an engine you’ll have. The simple answer here as to why a small-bore, long-stroke engine burns the charge faster, is that the flame front has less distance to travel,” says Fenske.

“By the time the flame front has reached the cylinder wall of the oversquare engine, the piston has moved further down the bore that in the smaller-bore cylinder, and you get less efficient combustion.”

If you really want to dive into some of the heavy lifting on the burn-duration subject, jump to the 11:34 mark in the video, where Fenske talks about a study he found and explains the results they published. It’s interesting, for sure.

While these examples are more illustrative than practical, they do get the differences in bore and stroke across in broad strokes. Fenske does end the video with a disclaimer, saying, “There are of course exceptions to everything we’ve discussed. Just because an engine has a large bore, doesn’t mean that it can’t be efficient. Just because an engine has a long stroke doesn’t mean it can’t make a ton of horsepower. But if you isolate those variables individually, this is what you’ll see.”

--   Regards,    Barry Gilkes  Max Torque Performance  P: 1-246-2343235  http://maxtorqueperformance.com

The whole idea behind building an engine is to capture as much air and the proper ratio of fuel in the combustion space as possible, squeeze it, light it off, and use the combustion to make pressure and power. One of the best ways to optimize that pressure is not to allow it to leak past the rings. This calls for not only a round cylinder but also one that offers the proper wall preparation in terms of a cross-hatch pattern and texture.

While this sounds simple, the execution of the process calls for some serious attention to detail. It doesn’t make much sense to invest thousands of dollars in trick pistons, rings, cylinder heads, valvetrain, and induction only to scrimp on cylinder-wall preparation. This installment of the EngineLabs Blueprint Series will introduce some current ideas you should seriously consider for your next performance engine build.

A Honed Edge

As a generic definition, the goal for a completed honed cylinder is to establish a perfectly round bore, sized to give the proper piston-to-wall clearance, with a given cross-hatch pattern and roughness. In addition to being perfectly round, the cylinder also needs to be perfectly straight in relation to the crankshaft.

The honing process employs a honing stone of a certain grit applied with precise pressure and speed, to create the desired cross-hatch pattern. The pattern on the cylinder-wall allows the rings to seal after a short break-in period while retaining enough oil to lubricate the piston and ring package properly.

Accomplishing the proper hone is more difficult than it might appear. When racers first started experimenting with cylinder bore finishes, their early efforts were aimed at creating a near-polished surface. This turned out to be less than desirable.

Later experiments revealed that a more optimal surface finish has a few microscopic peaks combined with deeper valleys. This offers the opportunity to store sufficient oil in the valleys to lubricate the rings while still providing a smooth enough surface to seal the rings to the bore.

This approach created what was first called a plateau finish back in the 1980s. The idea was to create the surface through a process first using rough stones to create the deeper valleys, followed by progressively-finer stones, combined with reduced load on the stones to flatten the rough peaks of the surface while retaining sufficient valley depth to lubricate the rings.

Setting Things Straight

Some of the earliest advances in ring-sealing science occurred when engine builders discovered that the cylinder becomes significantly out-of-round when the head is torqued to the block. To recreate this distortion during the honing process, thick torque plates are bolted to the block. These plates have openings in them, allowing the hone to access the bores.

The next logical step in the development process was to circulate hot coolant and/or oil through the block and torque plates to bring the block up to operating temperature, which simulates the block’s thermal distortion in the real world. We’ll save the exact details on how much that process is worth for a subsequent story, but the improvements are significant.

Perhaps the most impactful advancement beyond torque plates for the street engine builder is the integration of computer numerical control (CNC) over honing machines. Our recent experience with a Sunnen V-10 machine at our local machine shop revealed just how sophisticated this process has become. These advanced digital machines can now measure the actual concentricity and straightness of the cylinder DURING the honing process.

One aspect of cylinder honing often overlooked is how much the cylinder bore distorts — just from the action of the hone itself. It’s common to demonstrate bore straightness by using a dial bore indicator at various depths within the bore. While these measurements are accurate, they do not indicate whether the bore is vertically straight because each is a single point measurement.

A Different Kind of Stack of Dimes

An example of this is our photo of a stack of dimes. Let’s assume for a moment that this stack represents a cylinder of a given depth and each of these dimes is precisely the same diameter to 0.0001-inch. Let’s also assume that a dial bore measurement is performed on each individual dime. If the stack is offset as shown in the photo, the bore will measure the proper size at each particular measuring point, but in reality, it is closer to an “S” shape.

The latest digital honing machines from Sunnen, Rottler, and others will display the bore straightness as the hone is operating. Watching this can be a bit disconcerting as you see how much distortion really exists. These are expressed in shapes like a triangle (too small at the top or too large at the bottom), a barrel (too wide in the middle), or variations such as an hourglass or parallelogram. The machinist’s job is to minimize these distortions to create a truly “straight” bore.

This might also be a good place to mention that much of what we will discuss here is aimed at higher-end performance engines. This is not to infer that machine shops using older manual honing machines are not capable of doing quality work. Often, these shops are staffed with machinists having decades of experience honing blocks, who can deliver a high-quality finish-honed block that is as straight and round as they can make it, and with an excellent finish to boot.

Stylin’ and Profilin’

Taking the above concepts one step further, there is no replacement for being able to measure the results of a honing process beyond just bore size and straightness. Among the more significant advances in cylinder honing is a highly specialized tool called a profilometer.

This is a precision measuring device that can quickly evaluate the surface roughness of a cross-hatch pattern. The tool precisely measures the surface texture of the bore, and an end-user now has a highly accurate evaluation of the cylinder’s honing process. So, let’s get into a short explanation of these evaluations.

These descriptions come from the American Society of Mechanical Engineers (ASME), but rather than get bogged down in molasses-in-winter math, we will give you the abbreviated Cliff’s Notes versions of these evaluations. The measurements we will work with most are Ra, Rk, Rpk, Rvk, and the Mean Line.

There are several other values that take the express elevator farther down the rabbit hole than we prefer to go, so we’ll limit our discussion to the four values that revolve around the mean line. Keith Jones of Total Seal helped us with these descriptions to make sure we got this correct.

“Ra” is used to describe the overall average roughness of a cylinder wall. Ra is so generic that it has little useful application for cylinder walls. More helpful is the “Rk” number, which is the core roughness of the surface above what is called the “M line.” The M line is the mean, or the arithmetically-created middle line between the peaks and valleys, which is used as the baseline for measuring all of the following descriptions.

The Rk, or core roughness depth, is the description of the surface that will support the majority of the load. Think of this as the roughness of the base of the cylinder wall that the ring will slide across.

“Rpk” is the reduced-average roughness of the peaks created by the honing process. The Rpk numbers protrude above the Rk core surface This number indicates the average peak heights, which will wear down as the rings slide up and down the bore during the break-in period. A larger number indicates taller peaks while a lower indicates shorter peaks.

As you can probably guess, the “Rvk” number represents the reduced-average valley depth within a given lateral distance. These valleys extend below the Rk surface. A higher Rvk number — also expressed in µin — is equivalent to deeper valleys where more oil will be located. A good machinist will use a profilometer to measure the surface texture of his cylinder wall and adjust the roughness of the honing stones, the speed of his machine, and the load applied to the stones to achieve the desired surface finish.

From Theoretical to Practical

None of this information means much unless we can offer some examples. Several variables affect the desired numbers, starting with the hardness of the cylinder wall. Later model blocks like GM’s LS engines and most aftermarket blocks are cast from much harder iron than the engine blocks from the 1960s.

Another huge variable is how the engine will be used. Total Seal has chosen to identify three basic performance categories. Street engines would likely fall under Total Seal’s “General Purpose” class. Next would be Total Seal’s “High-End” classification, encompassing normally-aspirated competition engines. The top tier is nitrous and supercharged applications which Total Seal calls “Big Boost” applications.

We’ll offer some simple numbers for a given street engine. We’ve listed Total Seal’s honing recommendations in the included chart using the above three categories. Perhaps the best thing to take away from this is that creating the proper honing numbers for the appropriate rings depends largely on the way the engine will be used. One size, or in this case one honing plan, does not fit all.

We recently delivered a Dart Sportsman iron Chevy block to Brad Lagman at Quarter-Mile Performance (QMP) in Chatsworth, California to apply the final hone for an upcoming Total Seal ring test. Since the testing will include a set of ultra-thin AP CrN-faced rings, Lagman set up our block on his Sunnen SV-10 diamond-hone machine to address the cylinder walls.

If we compare the numbers generated from QMP’s profilometer on this block to the Total Seal numbers for a modern SV-10 Sunnen machine, we can see that Lagman did a really great job on the block. Our Rpk numbers are just slightly smoother than Total Seal’s General Purpose numbers while the Rvk values are slightly on the deep side of the General Purpose numbers.

This will place slightly more oil in the valleys, which should offer excellent lubrication to the rings while not creating a situation where oil usage might be a problem. The Rk numbers fall almost halfway between Total Seal’s “General Purpose” and “High End” values.

Looking at the Rk numbers more closely, our final number is lower, making it slightly smoother than the General Purpose numbers. This should improve the ring seal and help to minimize friction.

There’s far more to this subject than the introductory amount we’ve covered here, and we’ll save some information for a more in-depth story. In the future, we’ll look at specific honing techniques and other fascinating aspects of the process, such as what happens to a cylinder bore when the block is heated.

Everybody knows that ring seal is essential, but these highly specialized profilometer measurements become increasingly critical to properly sealing the rings to the cylinder wall in high-performance, high-cylinder-pressure applications. This is all part of what it takes to hone a block for a performance engine properly.

When you’re building an engine for a project there are limitless possibilities of parts and combinations you can use. If you’re jumping into the higher end of the horsepower pool you might be looking at using a set of aluminum connecting rods to swing your pistons inside the cylinder bores. Aluminum rods have long been a topic of debate in regards to their use and longevity in varying types of racing engines. Depending upon purpose, budget, power adders, and other variables, aluminum rods can be a great addition to any engine, but are they for everyone? And do today’s latest variants eliminate such concerns as rod stretch?

Anthony Giannone from MGP Connecting Rods joined us to illustrate the top five tips for buying aluminum connecting rods.

#1: Understand The Benefits Of Aluminum Rods Before You Spend The Money

If you’re making the investment to build a killer engine you want to pack it full with the best parts possible. The problem with that mindset is that you may end up buying parts that aren’t the best fit for your goals or the combination. Aluminum rods may seem like something you need because they’re shiny and fast guys use them, but you need to know if they’ll work for your build first.

• 
• 
• 

Aluminum connecting rods do provide performance advantages, but it’s important to ensure they’re the right fit for your combination.

Anthony has helped countless racers create engines that make enough horsepower to rotate the earth many times over and he provides a great explanation of aluminum rod basics.

“Aluminum rods are essentially shock absorbers. They’re intended to take all of the compressive load and not transfer that energy to the crankshaft; that was the original thinking behind the aluminum rod. So with that said, now anything that has a power-adder runs on detonation, and when you’re detonating that hard, a steel rod can’t live through that without failing.”

 The aluminum rod benefit is the ability to take that hit of energy and save the crankshaft. It’s a lot easier to justify a $1,200 set of rods than it is a $5,000 crankshaft if you need to replace something. – Anthony Giannone

The advantage that has been preached about aluminum rods since they were first introduced was the weight savings they provide. While aluminum rods can save you weight, they can also add strength to the right places.

“The topic of weight isn’t nearly as big as it used to be. Steel rod manufacturers have been able to remove a lot of weight in their modern designs, and aluminum rods are about 100 grams lighter in a direct comparison of similar rods. Engine builders are trying to get more weight off the piston these days and keep the extra mass at the bottom of the rod — that’s where an aluminum rod is beneficial. There’s a lot more material at the bottom, so they are still stronger for their weight compared to steel rods,” Antony says.

#2: Aluminum Rod Stretch And Growth Be Gone!

Rod stretch and growth used to be a legitimate concern for those who wanted to add a set of aluminum rods to their rotating assembly. Basically, rod stretch is the physical stretching of a rod’s center distance. An engine builder would have to take the stretch into account because the rods would grow as the engine increased in RPM. If the stretch and growth weren’t compensated for during the design of the engine package, when the rod would eventually stretch it would cause the piston to make contact with things it shouldn’t.

Anthony explains that at MGP, they don’t see rod growth anymore and assist their customers in making sure they have the right size rods based on this.

“People used to compensate anywhere from .010- to .015-inches center distance for growth that would occur when using aluminum rods. We recommend .050-inch piston to head, and that’s whether they want to put it at zero deck and run a .050-inch gasket, or put it in the hole .050 and run a .010 gasket. We just don’t see the rods stretching on the center distance like they used to. That distance is there just in case, because when we get rods back we don’t see them stretching really — they still have the same center distance we sent them out with.”

The rod stretch and growth plague might not be something you have to worry about as much anymore, but it took some work to get rid of. MGP spent a considerable amount of time working on finding a way to eradicate the problem so aluminum rods could become more practical for all applications.

“We eliminated that problem through design partially, and a lot through the materials we implemented into our products. The aluminum we use is an aerospace-quality material that is the most current aluminum to come to market. The material is what was causing the majority of stretch issues, and our new materials don’t have that issue. Getting rid of rod stretch and growth provides a performance advantage because people can run at zero deck and only have to run a .050-inch clearance,” Anthony explains.

#3: Torque Method versus Stretch Method For Rod Bolts

If you plan on building or maintaining an engine that uses aluminum rods you need to know how to properly torque the rod bolts. There are two different ways to do it: one is where you measure the amount of stretch once the bolt is tightened, and the other you torque the bolt down to a specific foot/pound measurement.

The stretch value of the rod’s bolt is important, because that is where the yield point is for the bolt, and it can’t be exceeded. If the bolt is stretched beyond its yield point, it will actually become physically longer and that will lead to it becoming weaker or having an uneven load put on the rod’s cap.

We use a torque value for our rod bolts, so both sides of the rod and both bolts are to the exact same foot/pound of torque. -Anthony Giannone

Using the torque method, you’re only torquing the bolt down to the specific amount the manufacturer recommends. You don’t have to worry about chasing a stretch value number or trying to get a stretch gauge to fit in a confined space under a car if you’re doing maintenance at the track.

“We use a torque value for our rod bolts, so both sides of the rod and both bolts are to the exact same foot/pound of torque. The bolt free length varies so much with different bolts that if you’re going off of stretch value, even if you’re setting static length on it, that bolt will be physically longer. When you finish the housing bore, keeping the same compression side to side is an issue going off of stretch value. Say on one side you’re at 90 ft-lb, and on the other, you’re at 98 ft-lb…. that housing bore isn’t being pulled an even amount on both sides. That can lead to an out-of-round condition for the rod,” Anthony says.

• 
• 

Using the torque method with aluminum connecting rods will keep them functioning properly and allow for easier maintenance at the track.

Using the torque method allows you to have a more precise measurement. Having the correct clamping load amount and keeping it even on each side of the rod cap is important, because that’s what helps the aluminum rod function at its best.

“The clamping load being even from side to side is ultimately the key to keeping the housing bore round, and that’s where the aluminum rods shine. When that housing bore is round it’s not collapsing vertically, it’s not opening the parting line up, and it’s not squeezing bearings. If you’re out-of-round right from the beginning it will destroy the bearings — it finds a way to side-load them in a weird way, and it will wear the coatings off of the bearings unevenly in places. All of those factors contribute to an aluminum rod failing when it shouldn’t in any situation,” Anthony says.

#4: Bolt Lubrication During Installation

Lubrication during assembly of aluminum connecting rods is a task that must be taken very seriously. Since you’re using a bolt that is made up of a different material than the rod itself, something needs to be used to fill in the area between each part.

“We’re dealing with two things here: first, we have the steel-on-steel contact between the bolt and the washer. Second, we’re dealing with the steel-on-aluminum contact between the thread of the aluminum rod and the bolt. Something needs to be added that can run interference between the two different metals — that’s why we use oil, and it also helps with the pre-load. The pre-load on the fastener is what really makes the connecting rod work correctly; when you lose pre-load, that’s usually when you end up with a giant hole in the side of a $10,000 billet block,” Anthony explains.

Most people would think that it’s time to reach for the assembly lube to make sure you have the correct bolt lubrication when assembling your rods, but that might not be the ideal course of action. Anthony explains why assembly lube isn’t your best friend when putting aluminum rods together.

“When you use assembly lube on bolts and torque them down, that lube is going to come in contact with engine oil when you fill the engine up, and those two liquids don’t mix well together. The particles in the assembly lube will grab the particles in the engine oil and will cause them to separate. That’s why I’ve always been against assembly lubes — because it ruins engine oil, and it can also plug up oil gallies if there’s too much used. When assembly lube heats up it will start to thin out and you lose the value you gain from it.”

So what does Anthony recommend for lubrication with rods? Surprisingly, the answer is just plain old 50-weight engine oil. This discovery was made after lots of testing to find a solution that would be the most consistent overall to torque down a rod bolt, because the oil remains neutral no matter what the temperature is around it.

“Zero- or 5-weight oil doesn’t stay as consistent because it is temperature-dependent. Fifty-weight engine oil is always going to be 50-weight with the same lubrication level, and has the same amount of molecules between the bolt and the rod no matter what the temperature is. It doesn’t matter if the rod and bolt are at two different temperatures, it stays consistent,” Anthony says.

#5: Billet versus Forged Aluminum Rods

You have two different options for aluminum rod manufacture: billet aluminum and forged aluminum. Forged aluminum rods are the original type of rod that was produced based on the technology that was available at the time. Now, companies can make rods out of billet aluminum, as well, and that added more options for builders.

The debate over which rod to use has always been based around the grain structure each possesses. To make a billet rod, MGP starts with a solid block of aluminum that’s 12-feet long and 3/4-inch thick. This material has grains that all run in the same direction from end to end. Making connecting rods out of this billet material wasn’t possible until the machines and processes were developed to make it happen. Now, a billet rod allows for more grain control and strength.

• 
• 
• 

Modern billet aluminum connecting rods provide strength in all the right places on the rod itself.

“The grain structure rolls around the rod end just like a forged rod would with a modern billet rod. Since we’re machining the rods out of solid stock, we’re letting the grain structure flow straight and we’re just machining through the center of it. The grains run the same way in that bar from end to end and we machine with the grain to make sure there is plenty of strength,” Anthony says.

Grain structure is important for a connecting rod because it dictates the strength of the part. The cross-sectional strength of the connecting rod comes from the design, while the overall physical strength is based on the aluminum itself. Having the grain structure of the aluminum all going one way, especially around the ends of the rod, is important to ensure it will have plenty of strength. Forged aluminum rods used to be the only way to provide this, but now with modern materials technology, a billet rod can be made of aluminum that has a good grain structure for a high level of strength. The biggest difference between forged and billet aluminum connecting rods is the service life — a billet rod will have a longer lifespan than its forged counterpart.

Aluminum connecting rods have come a long way since they were first introduced as an option for a rotating assembly. Understanding the limits of the part and how it works will help you make an informed choice if you need to use them in your next build.

There are numerous fables in the high-performance world on what you can or can’t do with various parts. One of the more common ones out there is that reusing MLS head gaskets is perfectly fine, but just because you hear something is true doesn’t mean it is. We talked with Mickey Hale from Cometic Gasket to see if you can, in fact, reuse an MLS head gasket.

Head gaskets are really what helps to keep all the fire inside the engine where it needs to be during operation. If a head gasket is compromised, all kinds of bad things will happen in a hurry that will hurt an engine and the owner’s wallet. Keeping the integrity of the gaskets intact will keep an engine running right and making plenty of power, so using a fresh gasket is very important.

• 
• 

According to Hale, the myth of being able to reuse a MLS head gasket has been around for a while, but it’s a bit misguided.

“While we see it on forums and message boards all the time about reusing MLS head gaskets and the success of the practice, its failure rate is much higher after reuse. The reason behind this is: once the gasket is heat cycled, the embossments will not spring back to where they were originally. In a mock-up situation, it is perfectly acceptable to install, check clearances and reuse the gasket. Once heat is put to the gaskets, the ‘spring’ is gone and since the embossment is the sealing area, there is a greater chance of a coolant or compression leak.”

Now, if you’re in a total bind at the track and need to reuse a gasket for only a handful of runs it’s not ideal, but it can be done. If you’re trying to reuse a head gasket as a long-term solution, that’s opening a dangerous door to many problems. The risks involved with not using a fresh MLS head gasket far outweigh the benefits enough to make it a good idea to keep a spare set on hand at all times.

“Besides the cooling leakage or a compression loss, oil retention could come into play. Most times with any MLS-type gasket, any leak is contributed to three things not being in play: proper torque settings, proper surface finish, and the gaskets not being fully compressed. An MLS gasket, when all three of these factors are correct, will not leak and hold a great deal of cylinder pressure. I would also say that adding an addition sealer, while it may seem like a good idea, really isn’t. The gasket already has a sealer on it, adding another layer of copper coat or similar keeps the gasket embossments from compressing fully to do what it was meant to do; think of it as hydraulicing the gasket in theory,” Hale explains.

If you want to learn more about MLS head gaskets and other engine sealing components check out the Cometic Gasket website right here.

In the engine tuning world, detonation is defined as one of the following: combustion that causes engine damage; combustion that causes banging or pinging noises; or combustion that causes power loss, bucking, or kicking. Detonation is not controlled and often unwanted. It occurs when fuel in the cylinder auto-ignites outside the intended flame front of the spark ignition.

Detonation does not always cause damage. At lower engine loadings during part throttle or low RPM, detonation may be warranted. For example, during the late ’70s and ’80s, pinging during normal operation was common with carbureted engines. Certain intake manifold design compromises combined with smog equipment caused lean fuel mixtures that burned outside of the controlled flame front from the spark plug.

Minor detonation sometimes occurs that is not heard through mufflers at low load or even with loud open exhaust. Major detonation causes a more severe noise during engine loading where the throttle is open and the engine is twisting hard against a heavy load.

Detonation and Preignition

Preignition is auto-ignition of the air/fuel mixture before the spark plug fires. The auto-ignition occurs at a location in the cylinder outside of the controlled flame front from spark ignition.

Similarly, detonation is auto-ignition of fuel, usually after the spark plug fires. Like preignition, detonation occurs outside of a controlled flame front from the spark plug. The term detonation is often used by racers as both preignition (before the spark), as well as uncontrolled burning after the spark. The same convention is used in this article.

Both preignition and detonation are from auto-ignition of fuel. They share characteristics — like a very high burn speed — which are comparable to explosive flame speeds. These include firearms muzzle velocities or explosives combustion velocities — typically well over 1,000 feet per second. The high velocity causes noise due to pressure fronts that collide within the cylinder.

Detonation and RPM

Detonation can be masked at higher RPM by high frequency noise, like that of an exhaust valve opening. It can be such a brief occurrence that it doesn’t cause damage before the exhaust valve opens, relieving the cylinder pressure and ending the detonation.

At lower engine speeds the time between detonation and opening of the exhaust valve is a longer interval, so detonation is more noticeable. As the RPM increases, it may sound like the detonation goes away because of shorter intervals between detonation and opening of the exhaust valve.

Racing engines in the ’30s and ’40s ran on lower octane gasoline, as higher octane gasoline was not yet developed. The lower octane fuels were susceptible to detonation as racers raised engine compression ratio for more power. Detonation was especially detectable at low engine speeds. To combat the low-speed detonation, those early racing engines were revved continuously at higher engine speeds to inhibit the effects of detonation.

If the engine was lugged by mistake, detonation could cause poor performance and possible engine damage. As a result, drivers coming into the pits for service would free-rev their engines continuously. Slipping the clutch to launch from the pits became an art form for many successful racing drivers. When starting in the pits, there was a great risk of engine stalling from a combination of inadequate clutch slipping, low engine torque at low-RPM, and detonation at low-RPM.

The best performance for modern day gasoline-fueled engines is achieved with a racing gasoline blend with an octane rating just high enough to avoid detonation. A gasoline blend with a higher octane rating does not usually increase performance by itself. Instead, the slower burn rate of high octane gasoline will often actually reduce an engine’s performance without other changes made to take advantage of the higher octane.

Gasoline’s octane need is characteristic of a specific RPM operating range. If that range is changed, a racing gasoline with a different octane may be needed. For example, if the engine spends more time under load at a lower engine speed, the engine may encounter detonation, whereas it would not detonate at the same load higher in the RPM range. A racing gasoline with a higher octane may be needed to combat the potential for detonation operating in the lower RPM range.

• 
• 

Illustrations from 5000 Horsepower on Methanol showing cylinder pressure vs. crankshaft angle for good combustion on left and detonation on right.

Dissociation From Combustion

Fuels dissociate, or break down, into different intermediate chemicals during compression, heating, and combustion. These intermediate chemicals can alter the auto-ignition temperature of the mixture from that of the original fuel alone. Many times, the wrong tune-up call is made because of detonation, assuming data based on just the properties of the primary fuel, when auto-ignition temperature changes from dissociation should have been taken into account.

In blown alcohol drag racing, competitors with higher static compression usually have to run a richer mixture than those with lower static compression to inhibit detonation. However, there is a point at which the need for additional enrichment tapers off. One competitor reported that beyond a certain point in compression increases, further enrichment was not needed, while the engine made more power with more compression. He continued to raise compression further and achieved national record-running performance. At a certain point, the extra-high compression was actually preventing the formation of detonation-sensitive dissociates.

Dissociate Causes of Detonation

With different racing fuels, some of the previously described dissociate formations can be more prone to detonation than others. The tune-up can affect the compression and heating which will affect what dissociates are formed, even with the same fuel. These dissociates then affect the detonation sensitivity. Additionally, air density changes affect the tune-up which, once again, affects dissociation in a vicious cycle.

For example, changing the closing point of the intake valve in a spark ignition racing engine will change the effective dynamic compression. Changing the compression changes the adiabatic heating and pressure from compression. Sensitivity towards or away from detonation can be triggered by something as simple as a camshaft change or even just retarding or advancing camshaft timing.

Pressure Changes Causing Ignition

Pressure changes the auto-ignition temperature of both the fuel and fuel dissociates, which can initiate detonation. An auto-ignition temperature of a fuel dissociate may be lower than the auto-ignition temperature of the fuel before it breaks down, which can be confusing, when looking at the data for the fuel alone.

During compression, say a mixture of air and dissociated fuel is below the auto-ignition temperature. The pressure wave generated in the cylinder can inhibit this mixture from igniting. However, as the pressure wave goes through the cylinder, it can trigger a change in the auto-ignition temperature of the mixture. Auto-ignition can follow as the pressure wave passes due to the accompanying drop in auto-ignition temperature, strictly from the chemical sensitivity change. Additionally, changes in the cylinder head from piston squish or unshrouding an intake valve can change the pressure wave formation and affect the combination’s overall detonation sensitivity.

Dissociation With Different Fuels

Gasoline

According to writings by the late Harry Ricardo (The High-Speed Internal-Combustion Engine, 3rd Edition, Blackie & Son Limited, 1950), who was a combustion engineering expert, unstable peroxides are formed as intermediate dissociates during gasoline combustion, which happen to be very prone to detonation. Tetra-ethyl lead is a reactive metallic addition that suppresses detonation from these unstable peroxides. In addition, various gasoline fuel constituents used in common blends have different dissociation properties to help combat the formations of the unstable peroxides. Examples of these constituents used are pentane, hexane, and toluene.

Fuel blending in modern gasolines is done to achieve detonation resistance, among other characteristics. In many racing gasoline brands, several are also blended with tetra-ethyl lead for the same purpose. Other characteristics such as chemical stability, ease of vaporization so that the engine can be started, and manufacturing cost, often limit blend additives and ratios. Those constraints can compromise the detonation resistance capability of some gasoline brands over others under given circumstances. The ideal result is a best-fit mixture or blend to fulfill the particular racing requirement, and why so many different racing gasoline variations exist.

Gasoline blends sold at the pump most often have seasonal changes in blend ratios and fuel content. Winter gasoline is blended for ease of starting, while summer gasoline blends are designed for vapor-lock avoidance. Different seasonal blends will change the dissociation and detonation characteristics, and needs to be accounted for in a performance application. Pump gasoline purchased in one season may encounter detonation issues if it is run in another season, due to the variance in blend.

Ethanol Gasoline Blends (E85)

E85 is predominantly (85-percent) ethanol with a small amount (15-percent) of gasoline added. The ethanol content’s high effective octane rating suppresses detonation in high-compression-ratio racing engine if the air/fuel ratio is rich. That would be a lambda of less than one in the EFI computer world. A rich alcohol fuel mixture also cools the cylinder away from auto-ignition temperatures. These rich air/fuel ratios can be run with a predominant alcohol fuel since alcohol does not foul out a spark plug like other fuels can. However, excessive richness reduces power output, so tuning the air/fuel ratio is vital. On the other end of the specturm, excessively rich mixtures can cool the intake too much, suppressing vaporization and inducing detonation from a vapor lean condition. This is the result of excess fuel condensation from cooling.

Methanol

Methanol as well as ethanol will dissociate into hydrogen and carbon monoxide during compression heating. Methanol and ethanol will also partially dissociate into hydrogen and carbon monoxide during boost in an engine with large enough pressures from forced induction, prior to, and in addition to piston compression. However, compression pressure retards the amount of dissociation that occurs. Therefore heat causes dissociation to go in one direction, and pressure from compression (or boost) causes dissociation to go in another. Combustion is then a combination of hydrogen, carbon monoxide, and any remaining methanol vapor that has not dissociated.

Differences in compression, engine temperature, camshaft timing, and boost in forced induction engines all affect the amount of dissociation that occurs. The amount of dissociation then affects the combustion characteristics of the charge. For example: hydrogen has very low ignition temperature and is more prone to backfiring into the intake, as it doesn’t necessarily need a traditional ignition source. That is often mistaken as detonation when, in fact, it is excess hydrogen dissociation that is reacting.

A tune-up or air density change can change the hydrogen dissociation and make or avoid engine backfiring. When backfiring from hydrogen dissociation occurs, subsequent engine disassembly often does not reveal any engine damage. The variation in auto-ignition temperatures of methanol is due to different amounts of dissociation from the tune-up and air density changes.

Methanol has oxygen in the fuel while traditional gasoline does not. As such, methanol can detonate with less air in the mix than gasoline. An air/fuel weight-ratio of 8-to-1 would be overly rich for gasoline and not detonate but could detonate with methanol fuel. That threshold changes with oxygen variations in the air from air density changes.

Nitromethane

Nitromethane dissociates in different phases. For a brief moment, some of these phases are sequential, and some are even simultaneous during the ignition and combustion process. However, many phases of nitromethane dissociation occur simply from compression heating and combustion.

The first phase is endothermic. It absorbs heat and acts like it is hard to ignite. This is why a magneto ignition with a long spark dwell time is more effective with nitromethane fuel mixtures to get past the first dissociation phase of combustion. The second and remaining dissociation phases of nitromethane combustion can be exothermic, that is, burning and giving off heat (Chem-Supply Material Safety Data Sheet, nitromethane, 1CHOP, December, 2000).

Multiple dissociation phases occur during combustion with different intermediate compounds and with different auto-ignition (detonation) characteristics. Different mixtures of nitromethane and methanol add further complexity to detonation sensitivity changes since methanol has its own set of dissociates and behaviors. As a result, the tuning directions can be troublesome and inconsistent from run to run.

Some nitro tune-ups may be more prone to detonation when leaning the mixture (higher air/fuel ratio). Some nitro tune-ups may be more prone to detonation with enrichment of the mixture (lower air/fuel ratio). The best tune-up routine is to make as few changes as possible to engine compression, boost, fuel mixture, fuel temperature, and others to dial-in engine power for the performance envelope. Making multiple changes from run to run makes it almost impossible to get control over the tune-up, because of that wandering auto-ignition temperature characteristic. Major engine failures can occur as a result.

Air/Fuel Ratio Changes

Changes in air/fuel ratio will also change the auto-ignition sensitivity characteristics. This change is complex depending on the amount of enrichment. Enrichment up to a point tends to decrease the auto-ignition sensitivity. Enrichment in methanol or ethanol can cool the cylinder temperature to where the engine will not detonate. Excess enrichment beyond a certain air/fuel ratio with those fuels can increase the auto-ignition sensitivity however. By causing excessive cooling and fuel condensation out of the inlet air charge, a vapor-lean condition is created and auto-ignition can occur. It can also slow down the flame speed, extending the combustion event into the exhaust stroke. That can lead to a backfire in the intake when the intake valve opens.

In the other direction, less enrichment beyond a certain optimum air/fuel ratio tends to increase the auto-ignition sensitivity. With methanol or ethanol, less enrichment will not cool the cylinder temperature enough, raising temperature enough to where the engine may then detonate, especially if high compression ratios are used.

Excessive reduction of enrichment may reduce power since there is less fuel to burn. Continued reduction of enrichment beyond a certain point may not detonate since the extreme lean condition results in a shortage of fuel to burn, and flame speed slows down. Somewhere in that lean direction, flame speed can be slowed, continuing past the exhaust stroke. That can then, like excessively rich conditions, cause a backfire in the intake.

Combination Effects are Complex

A nitro-methanol fuel mixture up to about 87-percent nitro, with increased richness, is less prone to detonation. That is the same behavior as most other fuels, especially alcohol fuels. However, a nitro-methanol mixture above 87-percent nitro with increased richness becomes more prone to detonation. That is because of an abundance of excess oxygen in the fuel. That excess oxygen in the higher percentage sensitizes the mixture towards lower auto-ignition temperature. A richer mixture of high percentage nitro mixtures has more excess oxygen and more detonation sensitivity.

If there is one thing to take away from all this, it’s that in a racing environment, the cause of detonation can be a complex issue, and isn’t as simple as “If X happens, then perform Y to fix.” When you’re at this level of performance the number of factors that could be affecting your power-robbing and potentially engine-damaging detonation issue requires a thorough understanding of what is happening with your fuel between the time it is first introduced to the atmosphere and the opening of your exhaust valve.

Looking for ways to generate horsepower during an engine build goes beyond displacement and the size of the ports on a cylinder head. Ensuring that everything inside the engine is sealed up correctly will capture every bit of power that’s on the table. Opting for a top piston ring that has been gas-ported will help keep that horsepower from escaping during the combustion process.

Gas-ported piston rings are the answer for racers when a gas-ported piston isn’t legal for the class they compete in. These types of rings can have a positive effect on blow-by inside the cylinder and create an opportunity for more efficient horsepower to be generated. Going to a gas-ported top ring isn’t just for exotic combinations–it can help any engine, from mild to wild.

Keith Jones from Total Seal expands on how a gas-ported top ring will help an engine that is used in a high-performance application.

“It allows increased gas pressure to get behind the ring and force it out on the cylinder wall. As we increase cylinder pressure, that same pressure is trying to push the ring away from the cylinder wall. We’ve got to get that pressure behind the ring and keep it loaded against the wall, and the gas-ported ring helps make that happen.”

Gas-ported rings have begun to find their way into many different engine packages as builders begin to feel more comfortable using them. One particular application that can benefit from a gas-ported top ring is one where a power-adder is in play.

“It is important on power-adder applications to get the increased cylinder pressure developed by that system to quickly get behind the ring, or those pressures will push the ring away from the wall. This causes a loss of ring seal and lubrication as the oil is then pushed back down off the cylinder wall. At that point, it all goes metal to metal, and that never ends well,” Jones explains.

• 
• 
• 

Jones goes further to illustrate how any engine can benefit from a gas-port top ring.

“Certainly anything you can do to improve ring seal is only a positive. There have been a fair amount of small-bore, high-output engines that have had gas ports from the OE–it’s pretty common in motorcycle stuff.”

The development of the gas-ported top ring didn’t happen overnight at Total Seal. To create the best possible product there was a good amount of time and research invested in the design, and Total Seal made sure they worked with customers to develop a ring that worked in real-world conditions.

“We did extensive testing with a select group of customers that we work with on these types of projects. So this is real-world development. We’ve got them in blown shootout style engines, sprint cars, dirt late models, and several other applications. It works very well when combined with our gapless feature. A gas-ported, gapless ring works great,” Jones says.

If you want to learn more about gas-ported top rings for pistons, check out the Total Seal website right here.

When you are building an engine, and you are trying to get the most possible power out of it, you start looking into different areas of optimization. One area that can be optimized in a number of ways, is the quench area. You can change combustion chamber designs, piston designs, and even head-gasket-thickness to adjust an engine’s quench area. However, before you can consider the pros and cons of different configurations and designs, you have to understand not only what it is, but what it does in the combustion process, and how that can help or hurt your end goal.

What is Quench?

Quench is the distance between the piston and cylinder head when the piston is at top dead center (TDC). Ultimately it can be thought of as piston to head clearance. The distance includes the piston to deck clearance and head gasket compressed thickness. Sometimes referred to as squish, quench is responsible for forcing the air-fuel mixture into the combustion chamber area near the spark plug.

Along with the obvious advantage of moving the air-fuel mixture toward the source of ignition, quench also reduces rich-lean spots, averages chamber temperatures, and accelerates flame propagation. Each of these improve efficiency, longevity, and overall engine performance. Therefore, quench area is certainly an important piece of engine design.

What are the Advantages of Quench Area in the Combustion Chamber?

If you think of quench as squishing the air-fuel mixture, it is easier to visualize the effect quench area has on the mixture itself. Imagine a puddle of water on the sidewalk as a young child in new rain boots leaps towards it. As the water gets squished between the excited child’s boots and the sidewalk, it moves rapidly outward creating a splash.

The water droplets that were puddled together are suddenly forced to separate and mix with the air above them. They accelerate from standing still to moving outward at a high velocity. Turbulence is created in both the air around the puddle and within the puddle itself. Now, transfer that visualization into the engine cylinder and the advantages of quench become clearer.

Reduces Rich-Lean Spots

An important aspect of intake runner design, especially in carbureted and throttle-body injection applications, is to keep the fuel suspended in the air stream as it approaches the cylinder. Air velocity is key in keeping fuel from dropping out of the air stream. However, the air-fuel mix quickly decelerates as it enters the increased area of the cylinder. The heavy fuel droplets fall out of the air stream and pool together.

Quench is responsible for introducing velocity back into the mixture. A tighter quench will obtain more velocity as it forces the mixture into the combustion chamber. Going back to the illustration of jumping into a puddle of water, tightening quench would be like increasing the boot size from toddler to men’s size 13.

“The higher velocity results in more of the mixture being ‘mixed’ and a higher percent of the A/F can be burned,” explains Mike Hupertz, testing and R&D engineer at Cometic Gaskets. “Now with this velocity there is turbulence. We know turbulence is less than ideal in the induction system, but we want to see as much turbulence as we can get in the combustion process. The more turbulence experienced while the piston is ascending to TDC, the more homogenous the A/F mixture becomes — resulting in a more efficient burn, basically more power with less unburned A/F.”

In other words, quench effectively reduces rich-lean spots. Temperatures in the combustion chamber are consequently averaged out. That means less chance for detonation and more consistent burn rates from cycle to cycle.

Accelerates Flame Propagation

The added velocity created by quench causes turbulence inside the combustion chamber. The result is a well-mixed dose of air and fuel. A consistent air-fuel ratio within the chamber offers more efficient combustion. In addition, the burn rate of the mixture is also affected.

Two separate processes occur during combustion. First is the most obvious and probably what comes to mind as you visualize the combustion process. Heat created by the ignition source, a spark plug in this case, raises the temperature of nearby fuel molecules to the point of combustion. As fuel combines with oxygen molecules during combustion, additional heat is produced, thereby starting a chain reaction, heating other adjacent fuel molecules to the point of combustion. This continues until the mixture is completely burned or is not able to effectively combust.

A second process is not as apparent. As temperature rises from the burning fuel molecules, pressure increases in that area resulting in a compression wave. The compression wave assists in spreading the flame but may also be responsible for detonation if too great for the fuel being used. These two processes are responsible for moving the flame front across the combustion chamber. This flame travel is referred to as flame propagation.

In order to have maximum cylinder pressure occur slightly after TDC, the ignition process must start as the piston is still ascending upward. That means pressure inside the combustion chamber is working against the piston for some period. Accelerating flame propagation allows for less ignition timing advance, and therefore reduces the amount of time combustion pressure is working against engine rotation.

Quench accelerates flame propagation in a couple of ways, both related to turbulence. First the homogenous mixture created from turbulence will burn more consistently. Lean mixtures have a slower burn rate than rich ones, and a perfect mix will burn the fastest. Reducing reach-lean spots in the chamber allows for consistent burn rates from power cycle to power cycle, and more precise ignition timing from one cylinder to the next. Second, turbulence itself accelerates flame propagation substantially, and it does so at or near TDC, again reducing the timing advance required.

Limitations and Considerations: How Much Quench Should I Run?

“We want the quench to be as tight as mechanically possible for the engine design.” That is the recommendation of Cometic’s testing engineer, Mike Hupertz. Cometic makes adjusting the quench area easy using their MLS (Multi-Layered Steel) head gaskets. These gaskets are comprised of a stainless-steel shim, available in various thicknesses, sandwiched between embossed and coated outer layers.

Engine Application Limitations

Although quench should be as tight as possible, there are limitations. Hupertz outlines some of the considerations that go into determining the ideal quench for specific engine designs:

“There are a host of things to consider when setting the quench distance: What is the intended use of the engine? Are there power-adders like nitrous oxide or a turbocharger? What is the maximum RPM the engine will see? Is the connecting rod material steel, aluminum, or titanium? How much piston rock is there at TDC?” asks Hupertz. “All of these have a direct effect on the piston to head distance. There are compromises that should be considered. For instance, a high-RPM, aluminum-rod, nitrous engine will need additional clearance that will not have ideal quench for a complete burn, but is a must if you want the engine to live and not self-destruct.”

Standard head gaskets typically have a compressed thickness around .040-inches. That works well for stock and most street performance builds if the piston is even with or slightly below the deck at TDC. If the rotating assembly height is taller than the deck height, the piston will protrude past the deck surface and may require a thicker gasket to give adequate clearance.

Quench should never be less than .035-inches. As Hupertz points out, the quench distance should be increased if the piston has enough rock at TDC to protrude above the deck. High RPM and aluminum connecting rod applications will require additional clearance as well due to their expansion at operating temperatures and high speeds.

Combustion Chamber Volume and Design Considerations

Combustion chamber volume and its overall design should also be considered. Chamber volume is the major component in determining static compression ratios. Situations where quench must be sacrificed in order to keep compression in check to satisfy a competition rule or accommodate existing parts, do arise. Increasing head gasket thickness is an easy and affordable way to reduce compression. However, reducing quench will also reduce efficiency and lessen resistance to detonation.

Overall design of the combustion chamber will determine how great the effect of reducing quench will be. Overall design includes the chamber area in the cylinder head as well as the piston which makes up the lower portion of the combustion chamber. Quench is most effective with wedge chambers and flat-top pistons. Consequently, it is logical to see a greater effect on engine performance and timing requirements when adjusting quench. Stepped-dish and full-dish piston designs reduce the area available to provide adequate quench.

Chambers that require a domed piston like hemispherical designs have very little quench. The result is a slow-burning chamber that requires more total ignition timing. However, the high breathing capabilities of a Hemi will outweigh that disadvantage. Fast-burn Pentroof designs are more common in modern engines. This becomes the best design in terms of burn-rate and flame propagation when quench is introduced.

The advancement in 3-D profiling and CNC machining allows for precise designs that OEM and aftermarket manufacturers use to maximize efficiency by allowing cylinder head combustion chambers and pistons to work together more effectively. Some aftermarket piston companies offer this level of design for custom builds, but that may be outside the budget of most performance enthusiasts. Understanding the advantages of quench, and the limitations specific engine applications may have on it, will provide enough insight for most to make educated decisions on head gasket thickness and overall chamber design for their given build.