Secret #3: Cylinder Head Basics
So we see that high rpm not only isn't always the route to added performance, but when it is the indicated path, it has its hurdles that must be dealt with. Being familiar with these issues is important. Finally, we come to high performance engine "secret" number 3 -- the four-stroke cylinder head. There is a lot of mystique surrounding the high performance four-stroke head. At the races, when a competitor is tearing down his engine, he will often wrap his cylinder head in a towel, away from prying eyes. Many have said that the four-stroke engine's camshaft is the heart of the engine. However that really isn't so. The camshaft is merely the "equal sign," the part that brings all the rest of the engine together. The real heart of the engine is the combustion chamber. Engine performance truly begins there.
So we see that high rpm not only isn't always the route to added performance, but when it is the indicated path, it has its hurdles that must be dealt with. Being familiar with these issues is important. Finally, we come to high performance engine "secret" number 3 -- the four-stroke cylinder head. There is a lot of mystique surrounding the high performance four-stroke head. At the races, when a competitor is tearing down his engine, he will often wrap his cylinder head in a towel, away from prying eyes. Many have said that the four-stroke engine's camshaft is the heart of the engine. However that really isn't so. The camshaft is merely the "equal sign," the part that brings all the rest of the engine together. The real heart of the engine is the combustion chamber. Engine performance truly begins there.
Combustion Chamber Shape
The shape of the combustion chamber is more important than many realize. It is far more important than what is done to the ports, or how big your carburetors are. Current combustion chamber technology has resulted in very flat combustion chambers. The reduced volume of this shape results in a shorter flame period, which means ignition timing doesn't have to be advanced as far. (The ignition advance required to get maximum power is in fact an indicator of how well the combustion chamber does its job.) In fact, modern engines run much less ignition timing than older ones do. The result is free power because for whatever number of crankshaft degrees that are saved, the engine is no longer fighting itself, with the piston compressing an already-burning mixture. Remember also that the piston is part of the combustion chamber. With their flat-topped pistons, high compression is possible in modern combustion chambers without detonation. There are no nooks and crannies in which harmful, detonation-producing end-gases can hide, enabling sport bike manufacturers to give these 86-octane-fed engines amazing 12:1 compression ratios. This new age engine's flatter pistons also present to its chambers less surface area and therefore they absorb less of combustion's heat. One of the advantages of the many multi-valve chambers we have today is that with so many valves in the chamber, these valves are more vertical, further allowing very efficient, shallow combustion chamber shapes. Older engine designs with more horizontal valves and necessarily deeper chambers are at a serious handicap, comparatively, and typically cannot run as high a compression and need considerably more ignition advance. One of the best aftermarket cylinder heads for the Harley Evo engine has the valve stems pulled toward each other, relative to stock, for more vertical valves and a shallower, better burning chamber. (Actually, the valve heads are moved apart, not the stems together. Consequently, this head works only on a very large big-bore cylinder.) Aftermarket heads like this one are the most effective items in the Harley performance market. Naturally, stock cylinder heads can't be improved by moving their valves around, but they can be reshaped to give at least some of the same benefit. Then there's squish. Squish, that area of the combustion chamber that serves to push end-gases toward the spark plug, to both eliminate end-gases and generate healthy charge agitation just before the spark, is a very important part of the high performance combustion chamber. So effective is every aspect of squish -- from its total surface area to its angle to its relation to the piston crown -- that racing teams usually guard each season's combustion chamber specs very carefully. Though the combustion chamber is often ignored by many engine builders, the professional has long known its the secret of its power potential.
The shape of the combustion chamber is more important than many realize. It is far more important than what is done to the ports, or how big your carburetors are. Current combustion chamber technology has resulted in very flat combustion chambers. The reduced volume of this shape results in a shorter flame period, which means ignition timing doesn't have to be advanced as far. (The ignition advance required to get maximum power is in fact an indicator of how well the combustion chamber does its job.) In fact, modern engines run much less ignition timing than older ones do. The result is free power because for whatever number of crankshaft degrees that are saved, the engine is no longer fighting itself, with the piston compressing an already-burning mixture. Remember also that the piston is part of the combustion chamber. With their flat-topped pistons, high compression is possible in modern combustion chambers without detonation. There are no nooks and crannies in which harmful, detonation-producing end-gases can hide, enabling sport bike manufacturers to give these 86-octane-fed engines amazing 12:1 compression ratios. This new age engine's flatter pistons also present to its chambers less surface area and therefore they absorb less of combustion's heat. One of the advantages of the many multi-valve chambers we have today is that with so many valves in the chamber, these valves are more vertical, further allowing very efficient, shallow combustion chamber shapes. Older engine designs with more horizontal valves and necessarily deeper chambers are at a serious handicap, comparatively, and typically cannot run as high a compression and need considerably more ignition advance. One of the best aftermarket cylinder heads for the Harley Evo engine has the valve stems pulled toward each other, relative to stock, for more vertical valves and a shallower, better burning chamber. (Actually, the valve heads are moved apart, not the stems together. Consequently, this head works only on a very large big-bore cylinder.) Aftermarket heads like this one are the most effective items in the Harley performance market. Naturally, stock cylinder heads can't be improved by moving their valves around, but they can be reshaped to give at least some of the same benefit. Then there's squish. Squish, that area of the combustion chamber that serves to push end-gases toward the spark plug, to both eliminate end-gases and generate healthy charge agitation just before the spark, is a very important part of the high performance combustion chamber. So effective is every aspect of squish -- from its total surface area to its angle to its relation to the piston crown -- that racing teams usually guard each season's combustion chamber specs very carefully. Though the combustion chamber is often ignored by many engine builders, the professional has long known its the secret of its power potential.
Camshaft Technology
No part of the four-stroke high performance engine embodies more mystery to the average enthusiast than the camshaft. There is a lot that is taken for granted about this usually very hyped-up component, but it is an interesting and quite simple fact that, just as the engine wants either MEP or rpm to make more power, likewise its valves want to be opened either farther or for a longer period to increase power. However, unlike MEP vs. rpm, both of which make more power, the power resulting from holding the valve open longer or opening it farther is very different in each case. Let's examine this. The idea of fooling with valve timing remember is increased volumetric efficiency. One of the ways the camshaft can contribute to this is by holding the engine's valve open longer. That is, by increasing the valve's open duration. This will potentially give more opportunity to the engine for cylinder filling. But there is a drawback. Exposing the cylinder to the outside for longer periods affects the intake and exhaust tracts by slowing the movement of their contents. The result is less optimum mixture distribution at lower engine speeds, because the fuel separates from the airstream when it is moving too slowly. In addition, extended valve duration cuts into the time the cylinder has to compress its mixture -- the engine has less compression. So while added valve duration usually offers a high rpm power increase, a side-effect is a loss of low rpm power. Another potential benefit of extended valve duration is that it usually increases valve overlap, that period during which both valves are open. As the valve overlap increases, the aforementioned pulse and inertia tuning of the intake and exhaust systems become dramatically more effective. However, again there is a drawback, and that is that the extended valve duration engine depends more heavily on pulse and inertia tuning to run well at all. Though powerful, pulse and inertia tuning is effective for only a very narrow rpm range. An engine cammed this way therefore runs better than stock, but only above s certain rpm, below which it runs much worse. The other way the camshaft can be used to increase cylinder filling, by opening the valve farther instead of holding it open longer, brings a very different effect. Like the valve that is held open longer, the valve that is opened farther allows more air into the cylinder, increasing power. However, since the time that the cylinder is exposed to the outside is not increased, the gases moving in the tract are not slowed, and the charge enters the cylinder still well mixed and combusts nicely. The result is no loss of low rpm power. Furthermore, since valve timing isn't changed, there is no loss of cylinder compression, and the engine isn't made more dependent on pulse and inertia tuning. Why then aren't all camshafts made this way, with an emphasis on lift instead of on duration, especially performance cams? There are three reasons. First, there is valve acceleration. The valve that is opened farther yet taking no more time to do so is one that is opened more quickly, i.e. accelerated harder. Remember that as the valve is accelerated, it tends to "float," and that float is the greatest danger in engines having old-fashioned spindly and flexible valve trains, which until a few years ago meant most of them. Second, because of the engineering world's historic fixation on valve duration, a certain politic of camshaft design has prevailed. It is still a cherished belief in many engineering circles that a valve never needs to be opened farther than 25 percent of its diameter. (Until the late 1980s, few if any production motorcycles deviated from this principle.) This 25 percent figure comes from an interesting geometrical fact. It happens that when the valve is open to a distance equal to 0.25 its diameter, the flow curtain around the valve's periphery is maximized. That is, it's a big as it is ever going to get. This is true as far as it goes, but like the old saying, it doesn't go far enough. There is more to this issue than flow curtain. The interesting thing is, opening a valve to 0.30d and more (racing engines open them to almost 0.50d) results in an interesting bit of trickery as far as time is concerned. For, larger openings actually extend the amount of time the valve is opened, without actually increasing valve open duration and thus adversely affecting tract speed and ultimately combustion. No, that is not a typo. More open time without more duration. Here's how it works. A valve that is open to 0.25d is at that magical full flow point only an infinitesimal period at operating speed. Almost negligibly, really. So the 0.25d flow curtain benefit is largely theoretical. However, when the valve is opened to say 0.35d (as most production sportbikes' valves are today), the valve then, by virtue of being opened past the 0.25d point, has some time to dwell at 0.25d, even though the total open duration is unchanged. Neat, huh? Finally, the third reason not many aftermarket camshafts are designed with lift in mind instead of duration is that such cams are very difficult to market. Its numbers aren't as impressive, for one thing. Plus, this kind of cam takes a lot more care to install properly, care that most engine builders unfortunately just aren't going to take. In fact, this is our next topic of discussion.
No part of the four-stroke high performance engine embodies more mystery to the average enthusiast than the camshaft. There is a lot that is taken for granted about this usually very hyped-up component, but it is an interesting and quite simple fact that, just as the engine wants either MEP or rpm to make more power, likewise its valves want to be opened either farther or for a longer period to increase power. However, unlike MEP vs. rpm, both of which make more power, the power resulting from holding the valve open longer or opening it farther is very different in each case. Let's examine this. The idea of fooling with valve timing remember is increased volumetric efficiency. One of the ways the camshaft can contribute to this is by holding the engine's valve open longer. That is, by increasing the valve's open duration. This will potentially give more opportunity to the engine for cylinder filling. But there is a drawback. Exposing the cylinder to the outside for longer periods affects the intake and exhaust tracts by slowing the movement of their contents. The result is less optimum mixture distribution at lower engine speeds, because the fuel separates from the airstream when it is moving too slowly. In addition, extended valve duration cuts into the time the cylinder has to compress its mixture -- the engine has less compression. So while added valve duration usually offers a high rpm power increase, a side-effect is a loss of low rpm power. Another potential benefit of extended valve duration is that it usually increases valve overlap, that period during which both valves are open. As the valve overlap increases, the aforementioned pulse and inertia tuning of the intake and exhaust systems become dramatically more effective. However, again there is a drawback, and that is that the extended valve duration engine depends more heavily on pulse and inertia tuning to run well at all. Though powerful, pulse and inertia tuning is effective for only a very narrow rpm range. An engine cammed this way therefore runs better than stock, but only above s certain rpm, below which it runs much worse. The other way the camshaft can be used to increase cylinder filling, by opening the valve farther instead of holding it open longer, brings a very different effect. Like the valve that is held open longer, the valve that is opened farther allows more air into the cylinder, increasing power. However, since the time that the cylinder is exposed to the outside is not increased, the gases moving in the tract are not slowed, and the charge enters the cylinder still well mixed and combusts nicely. The result is no loss of low rpm power. Furthermore, since valve timing isn't changed, there is no loss of cylinder compression, and the engine isn't made more dependent on pulse and inertia tuning. Why then aren't all camshafts made this way, with an emphasis on lift instead of on duration, especially performance cams? There are three reasons. First, there is valve acceleration. The valve that is opened farther yet taking no more time to do so is one that is opened more quickly, i.e. accelerated harder. Remember that as the valve is accelerated, it tends to "float," and that float is the greatest danger in engines having old-fashioned spindly and flexible valve trains, which until a few years ago meant most of them. Second, because of the engineering world's historic fixation on valve duration, a certain politic of camshaft design has prevailed. It is still a cherished belief in many engineering circles that a valve never needs to be opened farther than 25 percent of its diameter. (Until the late 1980s, few if any production motorcycles deviated from this principle.) This 25 percent figure comes from an interesting geometrical fact. It happens that when the valve is open to a distance equal to 0.25 its diameter, the flow curtain around the valve's periphery is maximized. That is, it's a big as it is ever going to get. This is true as far as it goes, but like the old saying, it doesn't go far enough. There is more to this issue than flow curtain. The interesting thing is, opening a valve to 0.30d and more (racing engines open them to almost 0.50d) results in an interesting bit of trickery as far as time is concerned. For, larger openings actually extend the amount of time the valve is opened, without actually increasing valve open duration and thus adversely affecting tract speed and ultimately combustion. No, that is not a typo. More open time without more duration. Here's how it works. A valve that is open to 0.25d is at that magical full flow point only an infinitesimal period at operating speed. Almost negligibly, really. So the 0.25d flow curtain benefit is largely theoretical. However, when the valve is opened to say 0.35d (as most production sportbikes' valves are today), the valve then, by virtue of being opened past the 0.25d point, has some time to dwell at 0.25d, even though the total open duration is unchanged. Neat, huh? Finally, the third reason not many aftermarket camshafts are designed with lift in mind instead of duration is that such cams are very difficult to market. Its numbers aren't as impressive, for one thing. Plus, this kind of cam takes a lot more care to install properly, care that most engine builders unfortunately just aren't going to take. In fact, this is our next topic of discussion.
Cylinder Head Set-Up
One of the most "secret" of all engine building techniques is proper cylinder head set-up. Many people assume that an aftermarket cam can be purchased from a catalog and put in the engine and away you go. Not so. But this is the perception, and this is why camshaft manufacturers can't sell really well-designed camshafts, but instead offer ones heavy in duration that any fool can install without trouble and get at least dubious results from. Most serious engine builders design their own cams. Check around and you will find that this is so. However, whether the camshaft you use is a custom or one off the shelf, it absolutely must be installed correctly. At the very least, that camshaft must be degreed, but that's another discussion altogether. There are an even dozen valve-related checks that must be made on the engine when installing the aftermarket cam. Following is an outline of those checks. Let's begin by defining some terms that may not be familiar to everyone, but all of which refer to the valve spring.
One of the most "secret" of all engine building techniques is proper cylinder head set-up. Many people assume that an aftermarket cam can be purchased from a catalog and put in the engine and away you go. Not so. But this is the perception, and this is why camshaft manufacturers can't sell really well-designed camshafts, but instead offer ones heavy in duration that any fool can install without trouble and get at least dubious results from. Most serious engine builders design their own cams. Check around and you will find that this is so. However, whether the camshaft you use is a custom or one off the shelf, it absolutely must be installed correctly. At the very least, that camshaft must be degreed, but that's another discussion altogether. There are an even dozen valve-related checks that must be made on the engine when installing the aftermarket cam. Following is an outline of those checks. Let's begin by defining some terms that may not be familiar to everyone, but all of which refer to the valve spring.
- Spring Free-Length:
Spring free-length means the length of the valve spring un-installed. This is usually the only specification given by the service manual. Its purpose in the stock engine is merely to identify the correct spring, and more importantly, to enable you to easily spot fatigued springs. However, high performance engine builders use spring free-length to calculate other important spring specifications. So we must start here.
- Spring Installed Height:
Installed height means the height of the valve spring once it is installed. In other words, the spring is already partly compressed even before the valve has moved. The purpose of installed height is simply to gauge valve seat pressure. Valve seat pressure is important in any engine, stock or modified.
- Spring Full-Open Length:
A spring's full open length is its length when the valve is fully open. This is the spring's shortest working length, and therefore it reflects the hardest that the spring will work. The primary purpose of spring full open length is to help the engine builder determine if there is sufficient spring pressure to control valve float, about which more will be said later.
- Spring Coilbind:
When a valve spring is coilbound, it is completely compressed, its coils touching one another -- metal to metal. This should never occur in operation, but we need to know when it could theoretically occur, so as to know how much room we have to stay away from it.
Now let's look at setting up an engine's valves and valve
springs for performance cams and pistons. The following twelve valve related
checks are performed on most four-stroke engines, though as noted, a few are
specific to rocker arm engines, and a few to shim and bucket engines.
- Installed Height:
As mentioned earlier, the spring's installed height is the spring manufacturer's way of ensuring that you get the correct valve seat pressure. The modified engine's increased cylinder pressure requires better sealing. Also, at high rpm there is less time for valve cooling, making good seating even more crucial. Some spring manufacturers use installed height in place of full-open pressure (our next step) to identify their springs and match them to the camshaft, though that is not the correct way. Checking installed height is easy. When the manufacturer's spec is available, simply assemble the valve components without the spring and measure how much room there is for the spring. In most cases, you will have to adjust the components to get the recommended installed height. If there is not enough room for the spring, this may mean sinking the valve deeper into the combustion chamber (the least desirable solution, as it will affect combustion), or machining the cylinder head spring seat area. If there is more than enough room, the spring can simply be shimmed to the correct installed height. If the spring manufacturer's spec is not available, as happens often with high performance parts for Asian engines, the process is a little more complicated. You must add together the spring's coilbind length, the maximum valve lift, and a 0.060" safety margin. The result will be an installed height that assumes you want the maximum seat pressure possible given the cam and springs you have.
- Full-Open Pressure:
All performance camshafts, whether duration or lift emphasizing, increase how quickly the valve opens, adding to valve acceleration and making controlling valve float a real problem. Increases in engine rpm that often accompany performance modifications further add to the issue. The spring's full-open pressure is your first line of defense against valve float, and it will often need to be considerably more than stock. There are two ways to determine full-open pressure, and both require a spring tester. You don't really need one of those $1000 units. There are several makes of small hydraulically-operated spring testers available that you can use in a bench vise. In method A, the length method, you must know the spring's installed height. Simply subtract from this the maximum valve lift, and compress the spring(s) in the spring tester to this length. If using method B, the pressure method, simply compress the spring(s) the amount of the maximum valve lift and note the pressure. Then mathematically add the known seat pressure.
- Valve Free Travel:
The valve's free travel, the amount that the valve can travel from closed to when there is guide interference, is very important. It determines retainer-to-guide clearance. Assemble the components without the springs, and measure from the bottom of the retainer to the valve guide seal. For safety, the amount must be 0.060" more than the maximum valve lift.
- Coilbind Clearance:
The purpose of checking for coilbind clearance, how close to coilbind the spring comes when operated, is to validate your spring choice. That is, it will reveal either over-shimmed or incorrect rate valve springs. Just repeat the full open test (length method) and then see if you can compress the spring 0.060" more without it coilbinding. If not, it's the wrong spring.
- Valve-to-Piston Clearance:
The relationship between the valve and the piston necessarily changes in an engine modified with a different piston or camshaft, or when the cylinder deck clearance or cylinder head surface are modified. In most cases, this relationship must change for maximum performance. That is, to make full use of an engine design, the valve must usually be brought much closer to the piston. This is by the way why so many Asian cars tangle their valves when their cam belt breaks, whereas American cars with similar designs do not. The Asian cars (and virtually all motorcycles) are built with much closer valve-to-piston tolerances, because maximum performance design usually makes better use of this clearance, resulting in less of it remaining. The two traditional methods for checking valve-to-piston clearance are the clay method and the indicator method. Method A (clay) -- If a hydraulic lifter engine, temporarily substitute solid lifters. Then lightly oil the combustion chamber and piston, cover the entire piston crown with a thick layer of clay, and reassemble the engine. Turn the crankshaft through at least two revolutions, and remove the cylinder head. After carefully removing the clay, bisect it and measure the valve-to-piston clearance with a caliper. Method B (indicator) -- Install soft (dirt bike carburetor) springs in place of the valve springs. If a hydraulic lifter engine, temporarily substitute solid lifters. Put a degree wheel on the crankshaft and find true TDC. After rotating the crankshaft to TDC overlap, place a dial indicator on the valve retainer and "zero" the dial. Then push down on the valve and note on the indicator how much the valve moves. Repeat with the crankshaft at 30o either side of TDC, in 10o steps. The valve needs to move at least 0.060".
- Valve-to-Valve Clearance:
Another potential problem area is valve-to-valve interference. This normally happens only when the camshaft is changed or larger valves are fitted. Two methods again. Method A is similar to Method B above for the valve-to-piston check, except insert a 0.060" piece of solder through the spark plug hole and determine whether the solder can pass between the valves. Method B is a Harley-only method, and requires that the manufacturer supply you with the "TDC lift spec," which is simply the amount the valves are open at TDC overlap. You simply put the valves in the head without springs or other parts, on the bench. Stop collar (using drill stops) the valves to the TDC lift spec, then see if you have at least 0.060" between the valves.
- Retainer-to-Rocker Cover:
These next three checks are rocker related checks that are quite common on Harley-Davidsons, though they may be appropriate for other rocker arm engines as well. On Harleys especially, the retainer-to-rocker-cover check is important. When the valve protrusion is increased on Harley Evos, as it often is, the valve spring retainer moves closer to the rocker cover, potentially interfering with it. Or, the cover may be aftermarket, or the heads, as is the case with most clone bikes, giving you the same potential problem. You want to avoid the valve spring retainer touching the rocker cover or any other casting. Assemble the head and rocker cover, and mark with a grease pencil where interference looks likely. Grind some clearance in there if possible. Sounds crude, but it's often necessary and you don't want to overlook it.
- Rocker Arm-to-Cover:
On Harleys again, changes to valve protrusion or any of the top end castings may cause the rocker arm to come closer to the rocker cover. Note the potential clearance issues on assembled parts and clearance as necessary. Clay can be used for this as in the valve-to-piston check. Put the clay on the inside of the rocker cover.
- Retainer-to-Rocker Arm:
This one is very common on modified Harleys and clones. The rocker arm contacts the valve spring retainer's edge due to larger than stock retainers or high valve protrusion. It can also result from incorrectly adjusted adjustable pushrods. The best Hot-Rod retainers are curved for this reason. Assemble and check.
- Rocker Arm Geometry:
Another frequent Harley issue, this is where the rocker arm's movement isn't evenly divided between opening and closing. The result will be excessive valve guide wear. Check to see that the imaginary center of the rocker arm shaft intersects the valve stem at a 90o angle when the valve is open to half its lift. This will divide the rocker's motion evenly, lengthening the life of the valve and valve guide. This problem is in fact why Harley-Davidson has a valve protrusion spec in the first place, and why shorter than normal replacement valves are widely available.
- Valve Follower Travel:
Leaving the Harley stuff now, and back to the import machine. Whenever camming a shim and bucket engine, you must check that the bucket (technically the follower) will in fact move the required distance. In some Asian cylinder heads, the bucket bottoms out in the casting a mere 0.100" or less after the stock valve lift. Failure to check this will result in a considerable amount of damage, including a broken camshaft. To check it, simply assemble the finished head with the bucket, and either dial-indicate or caliper-depth the fully closed bucket position. Then remove the valve and spring, put the bucket back in the head, and after letting it drop to the bottom of its bore, measure its position again. The difference between the two measurements should be 0.060" more than the maximum valve lift.
- Shim and Bucket Valve Protrusion:
Another common shim and bucket problem is that of assembling the cylinder head and then finding that even the smallest of the factory's shims won't get the valve clearances to spec. This can even happen on an un-modified head that has had a thorough valve job done on it. Usually, the problem is that the valve protrudes so much that the smallest shim will barely fit, if at all. Even if the smallest shim fits, you will then have no room left for future valve adjustments, which is not acceptable. On the old Z1, whose valves could be ground, the answer was simply to "tip" the valves 0.020~0.030", bringing the valve protrusion back down to factory spec. This enabled the middle size shims to be used for valve adjustment. However, on virtually every other engine, the valves are plated at their tips, so tipping is not possible. In this case, you must use aftermarket non-plated valves (such as stainless steel) and then tip them.
Summary
So now you know three of the best-kept secrets of high performance engine building. To recap, the first is that efficiency is important. Efficiency in at least three forms (volumetric, combustion, and thermal) is what the engine builder is really improving when he or she improves engine performance. The second "secret" says that rpm is half of horsepower. It is not all there is to power, as many assume. Rpm plays an interesting role, to be sure, but not the one most people assume. The third "secret" is that the cylinder head is the heart of the engine, where most of the real work of the engine takes place. It is also the hardest part of the engine to build properly, because it requires the most forethought, and nothing less than fanatical attention to detail.
So now you know three of the best-kept secrets of high performance engine building. To recap, the first is that efficiency is important. Efficiency in at least three forms (volumetric, combustion, and thermal) is what the engine builder is really improving when he or she improves engine performance. The second "secret" says that rpm is half of horsepower. It is not all there is to power, as many assume. Rpm plays an interesting role, to be sure, but not the one most people assume. The third "secret" is that the cylinder head is the heart of the engine, where most of the real work of the engine takes place. It is also the hardest part of the engine to build properly, because it requires the most forethought, and nothing less than fanatical attention to detail.
Well I hope you all enjoyed reading this article as much as I did. I know it is a ton of information, but it is all so helpful when building an engine that is going to run. Remember the next time you are building an engine to take your time, and make sure you do it right the first time!!! Enjoy!!!!!!!!!
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