Camshafts

Camshafts are, at one and the same time, both greatly misunderstood by most and worshiped by many.  That metal shaft with bumpy lobes can, all by itself, turn a mild grocery getter into a fire breathing 6,000rpm shredder.  Or can it…?

This is a picture of a Ford Model T camshaft. There are eight lobes, of course, for this four-cylinder engine. The inset profile of a cam lobe looks unconventional to modern eyes.

The fact that camshafts (“cams”) have been around for well over a hundred years in the automotive field has perhaps let them assume a persona that they don’t merit. Cams have come to be regarded as the “key” to performance, aside from most other components or factors.  They have a mystical aura about them.  Unfortunately, this doesn’t help you to understand them or, better yet, to intelligently select one for your individual application.

Of course, a cam is a device that has been used by humans for millennia in various small and large machines.  In the very earliest years of automobile design and production, using this rotating, offset circle to actuate a valve was the simplest solution.  And, so it remains.

This is a camshaft designed for flat hydraulic lifters, of which the majority of muscle car engines had. It’s actually a Pontiac ‘041’ Ram Air IV cam.

This is another V8 camshaft; If you look at the roundness of the lobes you can tell that this is a cam designed for roller lifters.

Camshaft Manufacturing

Most camshafts are made from chilled cast iron which is then machined into shape using conventional machine working processes. More expensive cams blanks might be forged, rather than cast, with a relative few parts being cnc milled out of billet steel. Chilled cast iron is used for most production camshafts, as it has a hard surface that can be further hardened by nitriding or induction hardening.

Assembled Camshafts are a recent development where cam lobes are manufactured separately and are then installed on a steel tube which is then expanded to hold the lobes in place. Sure, assembled cams are lighter than the one-piece traditional variety, but I believe their real advantage is that the lobes and the tube can each be constructed from materials that are ideally suited to their purpose.

Forging

Forging of metal has been around for millennia. In its typical form, forging subjects a heated metal part to repeated high pressure blows, which forces an alignment of the internal grain structure, resulting in a stronger part. If you can picture a sword maker hammering on a sword supported on an anvil, that’s one form of forging. The forging process can occur at temperatures characterized as cold, warm, or hot. Cold forging takes place at around room temperature, warm forging is at an elevated temperature that is below the crystallization temperature of the metal and hot forging is above that temperature.

All forging involves the application of high pressures to the material being forged, often with hammer-like blows. There are processes that utilize continuous pressures, as well.

An Eternal Tradeoff

Since the dawn of automobiles there has been a tradeoff between low speed and high speed performance. The term ‘high speed’ has changed over time, meaning above 3,000 rpm in the 1920’s and later indicating something above maybe 5,000 rpm, or higher.

The typical high-output muscle car engine is designed for its power band to be above 4,000 rpm. This means a high compression ratio, large carburetor, large valves and ports, free-flowing manifolds, and a camshaft with a lot of duration, overlap and lift. You might question the mention of compression ratio. A high-output engine is by default going to have a higher compression ratio than one designed for more mainstream passenger car service. Likewise, a more mundane engine will likely have a compression ratio compatible with less pricey, lower octane gas.

What happens to low-rpm engine output with an engine that is optimized for high rpm operation? Two things, (1) low airflow that won’t allow the fuel to remain well-mixed with the air, and (2) undesirable air flow due to excessive duration and the resulting overlap. The result is less effective operation at the lower engine speeds, with the most noticeable thing being the idle quality.

The ‘Perfect’ Cam Lobe Profile(?)

The ‘perfect’ cam profile is utterly ridiculous and totally unobtainable. But, as a thought experiment, what would it look like? It would open and close the valves instantly, and the valves would be either completely open or completely closed, with nothing in between. Again, can’t be done with the laws of physics we have. Ignoring that, what would it look like? I’d say that the lobe would be rectangularly shaped, right?

It’s About the Air

That it’s about allowing air (and, usually, suspended fuel) to move should be obvious.  When we use the term “air” when talking about cams, it’s understood that, with most older engines, it’s actually both air and the fuel suspended in it.  Sure, with later fuel injected cars, especially direct injected, it is just air itself.  Just keep in mind that “air” refers to air or air/fuel, whichever is appropriate.

‘Karman Line’? WTC?

We are at the bottom of a sea of air, our atmosphere, which compresses the crap out of the air that directly surrounds us.  The gasses of the atmosphere extend some 300 miles above the surface of the earth, but scientists consider the Karman line, 100,000km (62 miles) high, as the boundary between the atmosphere and space.  Yes, this is a bit arbitrary.  But consider that the air pressure at sea level is 14.7 lb./in² and that at an altitude of just 10,000 meters the pressure has fallen to about 10 lb./in². That’s a 32% drop in pressure at an altitude of a mere 1/10^th the height of the Karman line.  Clearly, the pressure drop relative to change in altitude is not linear.

It’s Always 212°F, Right?

If you live at a higher altitude than most, say 4,000 feet or higher, you might be aware that the lower pressure requires you to modify the procedure for some food baking.  That’s because water boils at 212°F at sea level only, where the air pressure is 14.7 lb./in². If the pressure is lower, as at a higher altitude, the boiling temperature of water lowers.  In fact, if you leave the pressure of our atmosphere completely, water can’t maintain its liquid state. 

While mars almost certainly has liquid water under it surface, its atmosphere is far too thin to allow water to remain liquid at its surface.  And you, being mostly water, would be in a lot of trouble on mars, even if you had an oxygen source. (Don’t you dare bring up that scene in Total Recall where the Arnie almost dies. I hated that. Oh, and Arnie isn’t an actor, either. Playing your own dumbass alter ego isn’t ‘acting’. Deal with it.)

My junior high science class desk mate, Janet the lovely, wasn’t too distracting for me to miss the fact that our atmosphere is mostly nitrogen (78%), with 21% oxygen and the rest trace amounts of argon, carbon dioxide, neon, helium, methane, etc. Of course, when it comes to internal combustion engines, we’re primarily interested in the 21% oxygen.

When discussing air flow, it’s really worthwhile to fully appreciate the fact that air moves due to pressure differential only, and that it flows from an area of greater pressure to an area of lower pressure.  A vacuum can’t “pull” air!  You don’t suck soda up a straw; you create a partial vacuum in the top part of the straw and air pressure pushes the soda up the straw in the process of moving from an area of higher pressure to an area of lower pressure (your mouth).  You might be tempted to say “yeah, big deal–it’s the same thing”, and it more or less is.  However, in visualizing and understanding air flow, it really is beneficial to have an accurate view of the forces at work.

An additional quality of air flow is that moving air has many of the properties of a fluid.  It stretches and compresses, speeds and slows, and constantly changes pressure as it does so. It can flow smoothly at times, and at others, tumble or swirl in ways that severely hinder its flow. We all know that liquids can’t be compressed to any significant degree.  They can be under pressure, though, the same as air.  Both, when forced through a smaller opening, will flow faster and at the same time exert less pressure on the walls of the object through which they’re flowing.  One place this really comes into play is with carburetion.

Consider the opening of an intake valve as the piston moves downward from top dead center.  The valve will have already started to open prior to the piston reaching top dead center (TDC).  As the piston moves down, an area of lower pressure is created in the cylinder and air rushes past the intake valve as atmospheric pressure tries equalize this lower pressure region.  The greater the pressure differential, the higher the air velocity will be.  It should seem reasonable to you that under some common conditions the air pressure in the cylinder will not have reached atmospheric pressure before the piston starts to rise on the compression stroke.

A Short Detour to Combustion

Now might be a good time to briefly address the combustion that takes place in the combustion chambers. After all, the camshaft should be designed for efficient combustion in the power band we’ve selected for the engine. This topic is covered more completely in the page Combustion and Fuel.

Regardless of the engine speed, what we ideally desire is as dense a charge of air that we need at the moment and the proper amount of fuel, well mixed with the air, to provide the air/fuel ratio that’s needed at this moment. That, of course, is going to be in the neighborhood of 14.7:1 for gasolene. This is the stoichiometric ratio for gasolene, with other values for other fuels.

Note that at part throttle operation, the carburetor butterfly valves are only partly opened and prevent the air pushed into the combustion chamber from being at atmospheric pressure. This is just what we want for part throttle operation. But what about full-throttle performance? We want the air charge to be as dense as possible, ideally at atmospheric pressure or above, with a correspondingly large quantity of fuel to be well-mixed with it.

We want this fuel and air to completely chemically combine, with no uncombined fuel or air. This is our unachievable ideal. There are many factors that oppose use in achieving this total combustion, but we won’t address them here. You might be surprised to know that the energy released by our combustion is largely from the oxygen that is consumed in the process, not the fuel itself. The fuel provides the hydrogen atoms that combine with the oxygen atoms to produce new molecules of H₂O and CO₂ (mainly), liberating a lot of energy in the process as the chemical constituents assume a lower energy state.

It’s the Oxygen!

No atoms are lost in the process. The atoms contained in the molecules of hydrocarbons and air (O₂) merely combine into a lower energy configuration, liberating energy in the process. Of course, it takes energy (heat) to initiate this chemical reaction, and the liberated heat energy supports its continuation. It takes energy to break apart the oxygen bonds of the O₂ molecules, but when the oxygen atoms combine with hydrogen or carbon (to form H₂O and CO₂) they release much more energy than it took to break them apart. More than anything, it’s the Oxygen that ‘contains’ the energy of combustion!

Yeah, It Happens Really Fast!

The pressure differential is constantly diminishing during the intake cycle.  Let’s say we were to calculate the approximate time air is flowing through the intake valve of an engine, say at 4,000 rpm.  That’s 66.7 revolutions per second. Since each cycle is two revolutions of the crank, we have 33.35 complete cycles per second.  We’ll approximate and say that the intake cycle represents 180° of this 720° total, or 25% of it.  Each complete cycle (2 revs) takes 29.8mS (thousandths of a second), so 25% of this is 7.5mS.  At 4,000 rpm, we have approximately 7.5mS for the cylinder to fill with air.  Of course, during this period, not only is the pressure differential varying, so is the intake area as dictated by the position of the intake valve.

Why Does Big Lou Sweat so Much?

Okay, let’s get a couple of things straight. I’ve had some friends who were of the larger size and they were fantastic people. I’m sure some were better than me. However, when I’m out and about and a see two large people getting into or out of a car, I will always say to myself “That’s asking a lot from that suspension” or something equivalent. If my wife is with me, I feel duty bound to express this out loud. She’s never, ever amused. And, no, I would never shame these people. I know how hard it is to lose weight, and that’s just the 20lb. or so I have to manage at times. Having established that I’m not a total ass, read on.

A large person has a lower surface to volume ratio than a small person. That allows them to lose heat more slowly, which is nice in winter but a pain in summer. This has nothing to do with ‘fat’ or ‘skinny’; we’re just talking about size. This applies to all objects, not just us homo sapiens.

It Matters, Dammit!

The relationship between the intake valve area and the volume of the cylinder is critical to the engine being able breathe well.  The larger the cylinder is, the lower the ratio of the intake valve area to cylinder volume is.  This assumes the intake valve is sized relative to the cylinder bore.

An easy way to visualize this is to use an extreme example.  Let’s say we have one cylinder that has a 4” bore and 4” stroke, and that the entire bore area is the intake. We have another cylinder with a 2” bore and 2” stroke, and with the same intake arrangement.  All dimensions are proportional. 

The larger cylinder has a volume of area x height, or (r² x π) x h, which is 50.26 in³.  For the smaller cylinder it’s 6.28 in³.  The large cylinder has a “valve” area of r² x π, or 12.56 in².  For the smaller it’s 3.141 in². The ratios of valve area to volume are 0.25 for the larger and 0.5 for the smaller.  Said another way, for the larger cylinder, each cubic inch is fed by 0.25 square inches of valve area, but for the smaller cylinder, each cubic inch is fed by 0.50 square inch of valve area!

That’s why a smaller cylinder tends to breathe better than a larger one, even with the relative dimensions kept the same.  In auto racing classes with displacement limits, you will find a large number of cylinders being used, far more than for a street engine of the same displacement.

The Four Cycles

We’ll start by reviewing the four cycles whose valve timing events the cam dictates.  Pay special attention to how the valve opening events get a head-start BTDC (intake) or BBDC (exhaust) and how the valve closing events are delayed until ATDC (exhaust) or ABDC (intake).  As you might expect, the higher the engine rpm the more important this becomes.

When picturing this it helps to keep in mind that air is elastic and like all matter, it has mass. It can’t be moved instantaneously. Even if the intake and exhaust valves could be opened and closed instantly, you would still need to give the valve events a head start in moving the air into the engine or the exhaust gas out. The higher the engine speed, the faster these valve events happen and the more of a head start is needed.

Moving Air

Maybe a good analogy for moving air would be the charging of a capacitor. The initial part of the curve is fairly linear (cap voltage vs. time), then it becomes increasingly non-linear. As the capacitor charges, its voltage rises and becomes ever-closer to the charging voltage. The lower the difference between these two voltages, the lower the rate of charge. You can see in the image below that the time is split into two periods, and that the voltage rises well over halfway in the first period. That’s because it’s in this period the difference between the cap voltage and the charging voltage is greatest. Air tends to exhibit a similar behavior, with its movement being greater the larger the pressure differential is.

This capacitor charging curve illustrates the concept of non-linear action, where the voltage charges to well over half of full-charge in only half of the time. Towards the end of the time period the voltage changes very little with time. Air pressure is similar to voltage pressure in that the lower the pressure difference, the lower the air flow.

Camshaft and Valve Motion

I think one thing that confuses us when trying to equate camshaft rotation (and valve actuation) to crankshaft rotation (and piston motion) is the fact that the cam rotates one time for two rotations of the crank. This is obviously reflects the nature of four-cycle engines, where one intake – compression – power – exhaust cycle takes two complete crankshaft rotations.

Some Acronyms

We’ll need these a bit later, so let’s get them out of the way now. Pay special attention to the fact that lobe centers, duration and overlap are all related to degrees of crankshaft rotation, while lobe separation angle is related to camshaft degrees.

• TDC                          Top dead center of piston travel (0°)
• BDC                           Bottom dead center (180°)
• ‘B’ prefix                  Before, as BTDC or BBDC
• ‘A’ prefix                   After, as ABDC or ATDC
• LC              Lobe centers; crankshaft degrees between valve fully open and closest piston dead center.  Intake and exhaust values may differ, but should be close.
• LSA                             Lobe separation angle.  Angle between cam intake and exhaust lobes, in camshaft  degrees.
• Duration          Intake or exhaust; degrees of crankshaft rotation between a valve opening and closing.  Measured to/from points where lifter is 0.050” from the bottom of its travel.  “Advertised Duration” does not observe this 0.050” value and is therefore a larger number, but far less meaningful.  Exhaust and intake values are often different.
• Overlap            Degrees intake and exhaust valves are both partially open, which occurs at the end of an exhaust stroke into the beginning of the next intake stroke.  Up to several tens of degrees of crankshaft rotation.
• Lift                     Amount that cam lobes ‘lift’ the intake and exhaust valves.  Usually same value for intake and exhaust.  Specified at an indicated rocker arm ratio (1.5:1, 1.6:1).  Directly related to cam lobe offset, but larger due to rocker arm ratio.
• Base Circle          This is the circular part of the lobe with no lift.
• Nose                     Center of the offset lobe; area of maximum lift.
• Ramp                Opening and closing; lobe section that transitions from the base circle to the nose.  Opening and closing ramps may have different shapes.
• Asymmetrical       The opening and closing ramps of a cam lobe have slightly different shapes.  Often this is used to have a fast valve opening and a slower valve closing.   Opposite is “symmetrical”.
• Dual Pattern      The lobe profile of an intake lobe is different from that of a closing lobe.

Intake

This cycle sees the piston moving away from TDC (0°), with the intake valve already having started to open several degrees BTDC, at the end of the previous exhaust stroke.  Somewhere toward the general vicinity of 90° of crankshaft rotation the intake valve reaches its fully open position.  The piston will be near its point of maximum velocity.  The crank rotation continues to 180° and BDC for the piston.  By this point the intake valve is almost entirely closed.  The high-speed flow of the air/fuel mixture through the intake valve has contributed to keeping the fuel mixed with the air, as this is not its normal tendency.

The important point in the diagram above is that early in the intake cycle the exhaust valve is not quite closed. A small amount of exhaust gas will be pulled back into the combustion chamber.

Compression

The Intake valve closes fully several degrees ABDC.  Only now can the cylinder really build compression, when it’s totally sealed.  Several degrees BTDC the mixture is ignited; this varies by engine speed, of course.  The compression stroke occurs between 180° and 360° crank rotation.

Early in the compression cycle the intake valve closing event impinges on this cycle. Ideally it would already be closed, but it was kept open longer to maximize cylinder filling at speed. A small bit of air/fuel will be forced back into the intake until the intake valve is fully closed.

Power

The piston reaches TDC (360°) and then the power stroke commences to transfer the energy from the hot, expanding gas to rotation of the crankshaft. 

When the piston is almost to BDC (540°) the exhaust valve starts to open.  Yes, this will bleed off the last bit of push the piston would have otherwise received, but the early opening start is important for complete expelling of the spent mixture, especially at the higher engine speeds. 

Exhaust

Now, the piston moving away from BDC (540°) pushes against the spent exhaust gas and forces it out the still opening exhaust valve opening.  As with the intake valve, the exhaust valve will reach its peak lift toward the middle of the piston movement from BDC at 540° to TDC at 720° (0° of the next cycle).  Some of the energy of the rotating crank assembly will be lost by the piston pressurizing the exhaust gas in the cylinder as gas tries to flow through the exhaust port.  Losses like this are termed “pumping losses”. 

Within several degrees of TDC, the intake valve for the next intake stroke will begin to open.  There will be a matter of several degrees where the closing exhaust valve and the opening intake valve are both slightly opened.  This, of course, is our overlap, which can be important to high speed power creation.  The effect of the increased purging of exhaust gas due to the still slightly open intake valve is called scavenging.

Valve Overlap

Overlap is the period of time that both valves are open and, in and of itself, is never desirable. It’s the unavoidable result of the ‘lead time’ given to the opening events of both the intake and exhaust valves. There is one period of overlap that starts on the exhaust cycle and ends on the next cycle, which is intake.

The start of the overlap period on exhaust is the intake valve starting to open at the very end of this cycle in preparation for the following intake cycle. Of course, the exhaust valve is open and still closing at the end of the exhaust cycle.

Overlap extends to the intake cycle, with the exhaust valve finally closing early in this cycle.

Why Can’t We Open and Close the Valves at the Top and Bottom?

It’s essential to understand that since air is elastic and has mass, our ability to force it to move has practical limitations. It might help to picture what things would look like with a ‘perfect’ camshaft. Furthermore, we could specify operation at a single rpm, at least for this thought experiment.

For the intake cycle, the intake valve would be open long enough for the intake charge to be at atmospheric pressure, but without starting to open too soon on the previous exhaust cycle, or fully closing much into the compression cycle. Since in our experiment we’re only interested in running at one engine speed, we should be able to dial in the valve opening and closing events pretty well.

The compression cycle is pretty simple in comparison. The intake valve has fully closed at, or shortly after BDC, so we didn’t force much mixture back into the intake in the early part of the compression cycle.

The power cycle completes. Since this is followed by the exhaust cycle, the exhaust valve starts to open a minimal amount BBDC, thus avoiding bleeding off pressure that would otherwise produce force on the piston.

For the exhaust cycle, the exhaust valve started its opening late in the previous cycle, to give us the lead we need to purge the combustion chamber of exhaust gas as completely as possible. Late in the exhaust cycle, the intake valve has already started opening, to provide the lead this cycle needs.

Summary

You could sum it up by asking two questions: “How much lead time do I need to provide the intake and exhaust valves for the intake and exhaust cycles, respectively?”, and “How much do we delay the closing of these two valves to assist in the intake and exhaust cycles?” This is primarily related to our speed of operation. Lucky for us this is just a single speed, so we don’t have to worry about operation at other engine speeds. Remember, we optimized our cam design for a single (general) speed, and any other engine speeds will be a compromise. That, my friends, is exactly what we see in the real world!

Two Extreme(ish) Examples

Let’s look at two examples. No, they might not be the most extreme scenarios, but we’ll run with them.

Load Hauler

If we have a vehicle whose primary focus is economy and/or moving loads, we’re interested in low rpm operation and will choose a camshaft to optimize engine performance at lower rpm ranges.

We therefore don’t need to have valve opening events that provide much lead, nor do we need to hold the intake or exhaust valves open as long. They can open later and close sooner. That means that we won’t have as much of an issue with air/fuel being forced back into the intake (compression), exhaust pressure being bled off into the exhaust (power), exhaust gas being forced into the intake (exhaust), or exhaust gas being pulled back into the cylinder (intake). Engines designed for low rpm power have smooth idle characteristics, as you might imagine.

Of course, in addition to having a camshaft that’s designed for low-rpm power, this engine won’t need huge ports and valves, nor will it need a huge carburetor. At the lower speeds the engine will see, it won’t be moving as much air as it would at higher speeds. Actually, a huge carb will hurt low speed performance because the large venturis will not keep the air and fuel well mixed.

A free flowing exhaust system won’t be needed, either. The compression ratio will typically be lower, given that the benefits of a high compression ratio are less important at low engine speeds. The cam won’t require as much lift, either, as that’s not important to an engine like this. Its rocker arms will be of 1.5:1 ratio, not the higher 1.6:1 to 1.75:1 of a high rpm, high output engine. Valve springs? Pretty basic; no fancy high rpm springs needed here. Lastly, the lifters used here will be maintenance-free hydraulic.

High-RPM Street Monster

Here we’re talking about a machine that’s optimized for high rpm performance, but that is still used primarily as a street car. Come to think about it, that’s what a muscle car was, isn’t it! This camshaft will have significantly more intake and exhaust durations, more overlap and more lift than the cam above. Its rocker arms will be beefier, and of a higher ratio than our ‘base’ engine. Valve springs will be more sophisticated in order to perform well at the elevated engine speeds this engine will see. Without question, we’ll have larger ports and valves, as well as free-flowing intake and exhaust manifolds. We might replace the exhaust manifolds with a set of well designed tube headers. The carburetor will be larger, and jetted to optimize high rpm power. A ‘hot’ ignition system will help ignite the air/fuel mixture at the high compression ratio and high engine speeds.

Of course, idle quality will be crap, with a rough action that exhausts a lot of unburned hydrocarbons. (Yes, I fully realize that this is sweet music to a lot of us!) Low speed performance will be soft, with this engine not really awakening until it reaches above maybe 3,000 rpm or so. Then the fun begins!

It’s too bad that we can’t have both low speed and high speed performance at the same time. More than any one thing, it’s the camshaft that prohibits this from being available.

Degreeing a Camshaft

To degree a camshaft serves three purposes:

1. Verify the cam lobe centerlines and duration are what they should be.
2. Verify the cam is aligned with the crankshaft
3. Optionally, allows you to check or set any desired advance of the cam.

The process of degreeing a camshaft is at once both straightforward and confusing. We’ll attempt to lay things out to that you can not only follow the procedure, but also fully understand it. I have always hated ‘instructions A – Z’ that just tell you what to do without understanding why.

This example is for the 1969/70 Pontiac GTO Ram Air IV camshaft.

Information from the cam card:

• Advertised Intake Duration: 308
• Advertised Exhaust Duration: 320
• Intake Duration at .050 Inch Lift: 230
• Exhaust Duration at .050 Inch Lift: 240
• Lobe Separation: 114
• Intake Centerline: 114
• Exhaust Close ATDC: 6
• Intake Open BTDC: 1
• Exhaust Open BBDC: 54
• Intake Close ABDC: 49

NOTE:

The following is just a bit of explanation about the two sets of duration and centerline. Look at the following timing circle diagrams as you follow the calculations.

• Intake 230° duration (0.050″) = 180° + 1° (intake open) + 49° (intake close)
• Intake 114° centerline = 115° (1/2 duration) – 1°
• Exhaust 240° duration (0.050″) = 180° + 54° (exhaust open) + 54° (exhaust close)
• Exhaust 114° centerline = 228° (LSA x 2) – 114° (Intakc CL)

The camshaft information above doesn’t address lift simply because we didn’t copy that portion of the information. You’ll see those values below, though.

Another Pontiac RA IV Cam Card

This is the key part of a cam card for the Comp Cams version of the same Pontiac Ram Air IV cam. Some of the values are slightly different from the values above, but that’s normal.

Lift is Sometimes a Confusing Thing

Take a look at the Comp Cams card above. There are two sets of lift values, ‘Gross Valve Lift’ and ‘Lobe Lift’. The lobe lift is taken right off the camshaft itself, while the gross valve lift is the lobe lift multiplied by the (default) rocker arm ratio of 1.5. Look at the intake lobe lift value of .313″; multiply by 1.5 and you get .470, which is the gross valve lift!

If your rocker arm ratio is different than 1.5, your gross valve lift will obviously vary accordingly.

If you’re looking at a lift value above .400″, it’s very likely a gross lift value, not lobe lift. Read your information carefully, and keep the difference straight.

Timing Circle Diagrams

Important: These diagrams use the Advertised Duration figures, which you would have used ‘back in the day’. All of the other values reference the ‘Values at 0.050 lift’. These values are marked by stars, green for Intake and red for Exhaust.

It’s key to remember that this timing circle is attached to the crankshaft, and we’re making two complete rotations of the crank and circle, for one complete cycle. The first image deals with the first two of the four cycles, Intake and Compression.

The second image addresses the third and fourth cycles, Compression and Power. The last image puts it all together into a single diagram.

Terminology:

• EOP Exhaust Opens (Ref. 0 lift; ‘Advertised’)
• ECL Exhaust Closes “
• IOP Intake Opens “
• ICL Intake Closes “

Intake and Compression

Follow the valve events clockwise around the wheel images; picture the wheels themselves as stationary.

Okay. We begin with the Intake cycle (IOP) at 42°, where the Intake valve begins to open. Note that the Exhaust valve is still in the process of closing, and is fully closed at 45° ATDC (Advertised) and at about 4° ATDC (0.050″). Some of the Intake charge escapes through the Exhaust valve, which is still closing.

The Compression cycle follows. The Intake valve is still in the process of closing, so some raw air/fuel mixture bleeds back into the intake manifold. Note that the IOP event belongs to the previous rotation of the timing circle and does not apply here.

Power and Exhaust

The Power cycle occurs next. The Exhaust valve opens at 85° BBDC (Advertised), and at about 50° BBDC (0.050″). This causes some of the cylinder pressure, which would otherwise do work, to bleed through the Exhaust valve. The Exhaust cycle, aided by the head start of the Exhaust valve opening, then purges the cylinder of exhaust gas. The head start given to the Intake valve for the following cycle causes some of the exhaust gas to move into the intake manifold.

All Together Now

This image inputs it all together, showing all events. You have to follow it around twice for a single cycle, ignoring the events that don’t apply to that time around the circle. Note the Overlap indicated, which is the period of time that both valves of a cylinder are not fully closed. As shown it’s about 87 degrees, referenced to Advertised durations.

What About the 0.050″ Values?

The ‘newer’ values, referenced to 0.050″ lift, will be used when you degree your cam. Other list values are 0.000″, 0.004″ and 0.006″. The cam card that accompanies a new camshaft will provide values referenced to 0.050″ lift and also values referenced to ‘Advertised duration’ of typically 0.004″ or 0.006″ lift. The referenced lift value will always be stated.

I suspect the value of 0.050″ lift was chosen as the standard because this could be considered to be either ‘just opened’ or ‘almost closed’. We’re talking about 1/20th of an inch, after all. It might also be argued that a person could more reliably measure an accurate 0.050″ than they could a lesser value, such as 0.004″ or 0.006″ (not to mention 0.000″). I’ve read that Harvey Crane of Crane Cams was the driving force behind the selection of this lift value.

Lobe Separation Angle

Lobe Separation Angle is related to the camshaft itself. If you look at the last timing circle above, you will see the LSA designated. Actually, this value, as indicated, is twice the LSA. This is because the camshaft turns at half the crankshaft speed, and the timing circle is attached to the crankshaft. This has the potential to confuse the hell out of you, but if you work through it, things will all come together.

106° to 109° is regarded as a narrow Lobe Separation Angle (LSA). Cams with a narrow LSA tend to have more overlap.

110° to 118° is regarded as a wide LSA. Cams with a wide LSA tend to have less overlap.

LSA and overlap are inversely related and it seems superfluous to specify both. I think it’s more intuitive to think in terms of overlap.

The Process of Degreeing A Camshaft

You need to have the following items prior to starting:

1. A degree wheel.  Given a choice, the larger the wheel the easier it will be to accurately read.
2. A bolt-on piston stop, to be used with the head removed.
3. A pointer to indicate position on the wheel.  This can be something flexible, like a clothes hanger.  You may want to either sharpen the end or attach something to make a finer point.
4. A dial indicator with a suitable mount and an extension.
5. The information card that came with the cam, if it’s a new installation.  Or, you might be checking what’s installed in an engine you did not build.

You would also benefit from having a notebook, pen, and possibly a calculator on hand. If you will need to measure piston-valve clearance, additional tools are needed (see below).

Finding Cylinder 1 TDC

The key to this is that if we use the piston stop to stop the piston while the crank is rotated CW and then when the crank is rotated CCW, true TDC is exactly between these two points (as indicated on our degree wheel).

Mount the wheel to the crankshaft and pointer to any conveniently close bolt.  If you don’t have a pointer, you can make one from a stiff piece of wire.

Rotate the crankshaft CW until the cylinder 1 piston is approximately TDC.   Position and tighten the wheel and pointer to the TDC indication.  This isn’t TDC, it’s just a starting point.  Back the piston off a bit, and mount the piston stop and set the adjustment bolt to almost contact the piston.  The stop should be set to allow the piston to rise close to TDC, but the piston should reach the stop first.

Rotate the engine clockwise until the piston contacts the stop. Write down the wheel degree value.  Then, rotate the engine counter-clockwise to the stop and record the wheel degree value. If your pointer did happen to already have been set accurately to TDC, your two recorded values should be the same.  That is, one will be Y degrees BTDC and the other will be the same Y degrees, but ATDC.  True TDC will be midway between these two points, so that’s where you want to position the pointer to indicate TDC. 

A Handy Little Example

Let’s say the first reading was 26° and the second reading was 34°, you would know that the pointer was 4° off and needed to be moved in the direction of the first reading (26°).  The wheel can be loosened and turned or the pointer moved, whichever is easiest. 

Now, repeat the above.  You should find that both readings are 30°, one BTDC and one ATDC.  If you adjusted the piston stop to allow the piston to come closer to its true TDC, the values you got with the CW and CCW crankshaft rotation would be less that the 30° in this example.  Regardless, TDC is midway between the two values.  Remove the piston stop.

In our example the degree spread as dictated by the stop was 60° total.  Had we adjusted the stop to achieve a lower spread, say 20°, our accuracy would not have been improved.  So, don’t worry about this.

Install the lifter in the number one intake lifter bore, with the indicator positioned securely above the lifter. The stem from the dial indicator should be aligned with the lifter as close as possible (misalignment will cause an improper reading). Turn the engine clockwise a couple of rotations. Enure the dial indicator is working freely and the lifter is not sticking or binding in the bore. Also check that you have adequate indicator travel. Rotate the engine clockwise until the lifter is on the heel, or base circle of the cam lobe (minimum lift). Zero the dial indicator.

Measuring 0.050″ Lift for Intake Opening

The engine should be capable of turning in either direction. Use a crank socket or other suitable tool to rotate the engine. At this point you will leave the wheel somewhat loose.

Install the proper lifter in the cylinder 1 intake lifter bore.  Position the dial indicator securely above the lifter. The stem from the dial indicator should be aligned with the lifter as close as possible. Misalignment must be avoided to get an accurate reading. Rotate the engine a couple of revolutions.  Then Rotate the engine clockwise until the lifter is on the base circle of the cam lobe and zero the dial indicator.

Rotate the engine further until the dial indicator shows 0.050″ of lift. The wheel indicator now points to the point of 0.050″ lift on the opening side of the intake lobe before TDC.  The point that you just identified should be the “Intake opens” spec on the cam card.

Check the Cam Card!

Compare the reading on the degree wheel with the “IN OPENS” specification on the cam card. If it does not match, your cam is either retarded or advanced. For example, if the degree wheel reading at 0.050″ comes up 12 degrees before top dead center (BTDC), and your cam card lists the 0.050″ intake opening at 8 degrees, your cam is 4 degrees advanced. If the degree wheel reads less than 8 degrees, your cam is retarded.  If it matches, your cam is installed as designed.

So, what do you do if your 0.050″ opening lift point doesn’t match the cam card (or you want to set your cam timing to something other than the cam card specifications)? There are several methods to adjust the valve timing:

• Degree bushings can be used on the cam sprocket to offset the cam locating pin.
• 3- or 9- keyway timing chain sets have additional keyways cut into them to index the crank sprocket.

‘Retarded’? That Ain’t PC!

Well, maybe not. Is ‘Advanced’? If the goal is achieving the most overall power (broadest powerband) and you have a method of adjusting cam position relative to TDC of the No. 1 piston (assortment of advance or retard keys, a multi-keyway timing chain), you can perform this process. Install the cam as recommended by the manufacturer. (For many street-level cams, the manufacturer grinds the cam 4 degrees advanced by default.) Measure the cranking compression in the No. 1 cylinder. This can be done even if the engine is not fully assembled. Of course, the number 1 cylinder piston/rod/ring assembly must be installed, and the valvetrain must be complete for this cylinder (rocker arms, pushrods, lifters, etc. ), and a functional starter must be present.

Compression Testing

This isn’t exactly like the compression testing you might do on an engine to check that all eight cylinders have adequate and consistent compression values. You want to make sure fuel and ignition are disabled. Here, we’re adjusting cam timing advance and/or retardation to find the position that yields the highest compression value.

The compression tester will screw into the cylinder 1 spark plug hole and the engine turned five or six complete cycles. You can use a remote starter for this, if desired. The compression gauge should capture the highest pressure reading. This should be somewhere between 125 psi and 175 psi. Make sure to write down your values, labeled with the advance value (plus or minus). If you are anything at all like me, you’ll say to yourself “Oh, I can keep these numbers straight”, and not write them down. Then, half an hour later you will be so totally confused as to have to start over, this time with the notepad you should have had in the first place!

You won’t have to worry about the engine accidentally starting, since the fuel system and ignition have been totally disabled. Still, there is the potential for injury if you don’t pay attention to what’s going on. Don’t be “that guy” who ends up in the emergency room because he exhibited monumental dumbassery!

Advance

Having completed the initial baseline cranking-compression check, advance the camshaft 2 degrees. As this procedure will alter the piston-to-valve clearance, be sure to check this before cranking the engine over (you really don’t want the piston and valve to touch!). Measure the cylinder cranking compression again.

Retard (No, not you!)

Next retard the cam the same amount and check the cranking compression again. You won’t have to worry about piston-valve clearance when retarding the cam.

Continue to either advance or retard the timing further, depending on whether the initial 2° advance or retarding yielded higher compression figures. Let’s say that the higher compression value was achieved by the initial 2° timing advance. You will then advance the timing by 4° (initial 2° plus 2°), again checking for piston-valve clearance. Work in the same 2° increments (checking piston/valve each time) until the compression falls, and then go back to the last (highest) advance setting.

If you’re working in the direction of retarding the timing, you won’t need to worry about piston/valve clearance. Why, you ask? Because in retarding the cam timing, the intake valve will start opening later. It’s the opening intake valve that might strike the still-rising piston at the exhaust-to-intake transition that is exacerbated by advancing the timing.

Checking Piston-Valve Clearance

This procedure verifies the clearance between the piston and both valves on cylinder 1. The other seven cylinders should reflect these clearance values.`

Install low-tension checking springs in the number 1 cylinder. Snug down the head to the block with the gasket in place. The gasket won’t be compressed to its installed thickness, but that’s fine. You will need to know the compressed thickness, which is listed on the gasket packaging. Measure the uncompressed thickness for a following step. Install the lifter, pushrod and rocker arm for the number 1 cylinder and adjust to zero lash with the crankshaft at TDC on the compression stroke. Both lifters are now on the base circle of the cam lobe.

Rotate the crankshaft to 10 degrees before TDC on the exhaust stroke. Position the dial indicator on the top of the exhaust-valve retainer and zero the dial indicator. Push down on the exhaust valve and note the distance traveled. Subtract the difference in the gasket thicknesses and you should have an accurate measurement of the piston-to-valve clearance.

Rotate the engine to 10 degrees after top dead center on the intake stroke.  Repeat the procedure with the intake valve and compute the clearance.

You can also use modeling clay placed on the piston where the intake valve comes closest to check clearance, too. This works, but it might be a bit harder to assign a value to the clearance.

You Might Need This

If you’re anything like me, you’re going to need this bit of explanation here. (I can’t be the only one…) When you measure the distance the valve moves while pressing down on it, you will be close to the clearance value. You still need to account for the fact that the head gasket isn’t compressed like it will be with the head installed. The difference between its ‘snugged’ thickness and its installed thickness reduces the clearance value you measured.

The Tools of the Trade

What’s Old is New!

One of my used book store treasures is High-Speed Combustion Engines, 1941 edition. The first edition dates to 1916! Some sections of this book are thick with integral formulas and trigonometric proofs. I found it has more than a few surprises that struck me as remarkably contemporary.

The sections on camshafts and valvetrains was a treasure trove of information, most of it still applicable. Overhead cams were explored, as were solid and hydraulic lifters, including an early roller lifter for tangential cams!

Camshaft Types

‘Back in the day’ all cams used solid lifters, usually called ‘tappets’, and tappet adjustments were a regular part of maintenance. Even after hydraulic lifters were invented, solid lifters remained the norm.

Hydraulic lifters became common and surpassed solid lifters in popularity in the early ’50’s. This freed car owners from the periodic tappet adjustments. The drawback? Increased manufacturing costs.

Roller lifters became common in the 1980’s. These were usually still hydraulic, but rather than the flat surface of a cylinder riding on the cam lobe a small steel roller was used. You might be tempted to think that this was to reduce friction, but you would be wrong. The lifter roller contacts a cam lobe in what is essentially a line; this allows it to follow a much more aggressive lobe profile than a flat-tappet lifter ever could.

Flat Tappet Cams

Solid Lifters/Cams

Back in the muscle car era there were a relative few high-output engines that used solid lifter cams rather than a hydraulic cam. These included most years of Chrysler’s 426 Hemi and the hottest varieties of Chevy’s Mark IV big blocks. Why? The answer is that some of the hottest cam lobe profiles had valve opening and closing velocities that were unsuitable for hydraulic cams. The portions of the lobes that are different are the points just before and after (adjacent to) the lobe base circle.

Why would you want to use a solid lifter cam? Two things: a more aggressive profile than a hydraulic and the ability to operate at higher engine speeds than a hydraulic cam can. Hydraulic lifters can over-pump at engine speeds that are higher than they are designed to accommodate. This will result in valves not fully closing. With solid lifter cams you will need higher valve spring pressures than for hydraulic lifter cams. An additional aspect of solid lifters is that they have less mass than hydraulic lifters and therefore contribute less to valve train mass, which becomes increasingly difficult to control as engine speeds increase. These forces increase with the square of speed.

With solid lifter cams you must have some way to adjust the lash, or slack, in the valvetrain. The general way is with adjustable rocker arms, although sometimes adjustable pushrods are used.

My Lobe is Not Symmetrical!

Well, that’s normal, so don’t worry. Everyone has some asymmetry…Oh, wait. We’re talking about camshaft lobes, aren’t we? Nevermind.

Some camshafts have lobes that aren’t symmetrical, usually with the valve opening ramp being designed for faster valve motion than the valve closing ramp provides.

Dual Pattern

In addition to the above, many cams are of a dual pattern type where the intake lobes and exhaust lobes are of a different shape, with different durations, including possibly yielding different total lift figures. It’s generally believed that this type of cam was developed to address flow differences between intake and exhaust ports. This term can apply to all types of camshafts.

Hydraulic Lifters/Cams

This has been the most common lifter type since the early 1950’s, due to its lack of required periodic adjustments. Recall that most muscle car engines from back in the day had hydraulic lifters and cams, with only the baddest of the bad using solid lifters/cams. These engines were optimized for high-rpm power in most aspects of their design, not just the cam and lifters.

It should be noted that it is possible to get special rocker arm lock nuts for hydraulic cams that will limit lifter plunger travel to avoid over pumping.

One source makes the quite believable claim that hydraulic lifters simply can’t over-pump by overcoming the valve spring pressure. Rather, they argue, it’s the high-rpm valve float that allows the over-pumping. This makes sense to me.

Both types of flat-tappet cams have their bases very slightly convex, with the center 0.001″ to 0.002″ higher than their circumference. The cam lobes aren’t perfectly flat, either, with a taper that is from 0.0007″ to 0.002″. The purpose of this is to force the lifters to rotate.

Roller Lifter Cams

Roller lifters came into popular use in the 1980’s. The primary benefit of roller lifters is that the roller that contacts the cam lobe can follow a much more ‘aggressive’ profile than a flat-tappet lifter (solid or hydraulic) could. Roller lifters tend to be hydraulic, but there are solid roller lifters for ultimate high-rpm performance.

Unlike flat-tappet cams, roller cams don’t need the slight lobe taper. Roller type cams require quite high spring pressures. If the rollers were to lose contact with the cam lobes, the resulting crash back would be potentially catastrophic to the roller bearings.

Here are some lifter resources:

• https://www.youtube.com/watch?v=ALi7-xnlRV0 That Engine Guy; about LS engines, but really good stuff.

Valves

The obvious difference between intake and exhaust valves is the size of the head of the valve. It wasn’t always this way (see below), but it was realized early on that with a fixed area for both valves, making the intake valve larger, at the expense of the exhaust valve size, would result in much better performance than if both valves were the same size.

Why the above statement is true should be fairly obvious. The exhaust valve flows hot exhaust gas that’s under considerable pressure, versus the intake valve that sees atmospheric pressure air. The ratio of intake valve area to exhaust valve area is loosely fixed at around

Here we have a Pontiac intake valve of a ‘regular performance’ variety.

This picture is of the top of a Pontiac high-performance intake valve. Note the dished center, which is because this valve is of the ‘tulip’ variety.

Here’s the bottom of the valve directly above. You can tell how the stem blends into the head of the valve.

This isn’t any particular valve of interest, but it does nicely show the ‘tulip’ effect. This type of valve is more expensive to manufacture, but it flows considerably better than a conventional type of valve.

Valve Materials

Valves are made from two different types of steel, ‘austenitic’ or ‘martensitic’. The term ‘austenitization’ means to heat the iron, iron-based metal, or steel, to a temperature at which it changes crystal structure from ferrite to austenite. The more-open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel.

Martensite is formed in carbon steels by the rapid cooling (quenching) of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe₃C).

Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe₃C. It is 6.67% carbon and 93.3% iron by weight. It’s a hard, brittle material. There are other forms of iron carbide.

Martensitic Steel

In martensitic steel, the steel is “quenched” (cooled) very quickly from a molten state to freeze the grain structure in a particular configuration. Under a microscope, the grain structure has a needle-like appearance. The result is a steel that’s very hard but also brittle. Reheating and cooling the steel (a process called “tempering”) allows some of the martensite crystals to rearrange themselves into other grain structures which are not as hard or brittle. By carefully controlling the heat treatment and quenching process, the hardness and tensile strength of the steel can be fine adjusted to achieve the desired properties.

Steel alloys with a martensitic grain structure typically have a high hardness at room temperature (35 to 55 Rockwell C) after tempering, which improves strength and wear resistance. These characteristics make this type of steel a good choice for applications such as engine valves.

Martensitic steel loses hardness and strength as temperature elevates. Above 1000° F or so, low carbon alloy martensitic steel loses so much hardness to result in compromised structure. This is why low carbon alloy martensitic steel is only used for intake valves, rather than exhaust valves. Intake valves are cooled by the incoming air/fuel mixture (not with direct injection) and typically run roughly 800° to 1000° F, while exhaust valves usually operate much higher, at 1200 to 1450° F.

Some ultra-high-performance intake and exhaust valves are made of titanium. You can plan on spending roughly $150 for each of these things!

Sodium Filled?

Some high-end, high-performance engines take special measures to cool exhaust valves. This involves using a hollow stem and partially filling this interior with a sodium substance. Liquid sodium is a shiny, liquid metal. It forms when sodium metal reacts with water, releasing so much heat that the sodium melts. Liquid sodium is used as a heat transfer fluid in sodium-cooled fast reactors.

The sodium in the valve stem becomes liquid at about 208 degrees. It moves up and down within the stem, aiding the transfer of heat up the stem and into the valve guide.

This practice actually started with aircraft engines, which can be under substantial load for hours on end. The primary cooling for this valve is the brief time it’s closed, which allows it to transfer heat via the wide valve seat. Exhaust valve seats are generally about 0.100″ wide while those for the intake valves are about 0.060″ wide. The wider exhaust valve seat aids cooling.

Seats

Valve seats can be made of a number of different materials. Powdered metal is one of the materials of choice for today’s engines or rebuilds. Powder metal seats are made by mixing together various dry metal powders such as iron, tungsten carbide, molybdenum, chromium, vanadium, nickel, manganese, silicon, copper, etc.), pressing the mixed powders into a die, then subjecting the die to high heat and pressure in a process called ‘sintering’. This causes the powders to bond together and form a solid composite matrix with very uniform and consistent properties.

Valve Guides

Valve guides not only ‘guide’ the valve, they also help ensure the valve stem receives adequate lubrication. Depending upon application, they are constructed from cast iron, brass/copper, copper/bronze, or manganese/bronze.

Guides are press fit into place.

Valve Stem Seals

These parts are made of various materials and have a rubberish character, their purpose being to limit the amount of oil running down the valve stem. They fall into three categories, positive seal, umbrella seal and O-ring types. The positive seal type fit around the valve guide boss in what is probably the most intuitive manner of the three types, whereas the umbrella type fits onto the valve stem itself and moves with the valve. Its shape, like an umbrella (Duh) shields the part of the valve beneath it from oil that is pumped up to the rocker arm via the hollow pushrod.

The O-ring type fits around the valve stem just below the keeper groove, into a groove of its own. This O-ring provides a seal between the retainer/keeper to the valve stem. Kind of like the umbrella seal, this stops oil from being able to run down the exposed part of the valve stem and into the valve guide.

It should be noted that some oil lubrication will still make its way down into the valve guide to lubricate the valve stem within the guide. This is essential, with any of the three types of seals simply preventing an excessive amount of oil from causing problems with oil burning and excessive oil consumption.

Valve Springs

Generally speaking, if the valve springs are able to keep the lifters in contact with the camshaft lobes, even at high engine rpms, everything will be fine. Unfortunately, there are many way that this can go wrong!

There are about four general valve spring types, the selection from which depends mostly on whether your engine is intended for high rpm operation or not.

I looked at one aftermarket manufacturer’s valve spring offerings and saw that a set of 16 started at $60 and went up to $240. This is just to give you some idea of what the market looks like.

Valve Spring Materials

As you might imagine, there is a good bit of science and technology that go into the design and manufacture of valve springs. Some of the materials that are used in the manufacture of valve springs include the following:

• Stainless Steel
• Titanium
• Hard drawn High Carbon Steel
• Chrome Silicon
• Monel
• Copper or Nick-Based Alloys
• Chrome Vanadium

Regardless of the type of valve spring, some of the essential characteristics are high stress tolerance, good elasticity, and heat resistance.

Manufacturing Valve Springs

Wire stock is pulled through (‘extruded’) increasingly smaller dies until it’s the desired size. This is done without heating. The wire is cut and then heated and wrapped around a form. Both ends of the spring are ground flat. A shot peening process follows, and there may be additional steps, including an optional painting.

Choosing Valve Springs

There are many things that go into the selection of valve springs and I’d advise you to both educate yourself and then seek consultation from one or more manufacturer experts. Choosing the wrong springs or incorrect installation can have catastrophic consequences.

One thing that is absolutely essential is that you don’t experience valve spring binding. If the valve spring compresses fully so that coils of the spring touch, having no more space between them, AND the cam lobe is still lifting the valve, you have valve spring binding. Something will break and much unhappiness will follow. Possibly embarrassment, too.

There are a few things that are essential in choosing valve springs. First, it has to fit the head it’s installed on. You need to know what kind of pressure values you want with the valve closed and with the valve opened. The valve-opened pressure depends partly on the valve lift you ‘re going to have. Does your cam provide additional lift? Did you go to rocker arms with a higher ratio? These factors will affect how far your valve opens, and you need to know the valve spring pressure at full lift and also that your springs can accommodate this lift without binding.

Lots of Pressure!

Your valve springs will need to apply 300 – 400lb. (ballpark) pressure with the valve fully open and maybe from 125 – 200lb. when closed. Obviously enough pressure needs to be provided to keep the lifter from ‘launching’ off of the cam lobe nose at high rpms, and it also needs to provide enough force to keep the closed valve from bouncing open.

A valve spring manufacturer will specify clearances necessary for you to avoid spring binding, as well as other assistance in selecting the right product from their catalog.

Here are some resources for you to make use of if you’re going to be choosing valve springs:

• https://www.youtube.com/watch?v=xsuDuHA8f2g From realstreetperformance.com. Pretty good video.
• https://www.youtube.com/watch?v=_gNlgnHdq1o Scoggins-Dickey; rather specific to LS engines.

Example of Valve Spring Specs

This is just one page of a valve spring section of a catalog. A few thoughts about some of the specs:

• Spring Rate is per inch of lift. A value of 324lbs. with a list of 0.500″ would yield a value of 162lbs., which would be added to the pressure at installed height (valve closed).
• The Spring Loads values are for the indicated lift values. Using the value above (for 26123 p/n), if we had 1.300″ installed height, the closed pressure would be the value indicated, 145lbs. The pressure with the valve fully open is then 162 + 145 = 307lb.

Retainers and Keepers

These are the bits that keep the valve springs connected to the valve. Simple enough.

This is a data sheet for a random valve lock, showing the information you can expect to see when shopping for yours:

• Brand: Melling
• Manufacturer’s Part Number: VL-200
• Part Type: Valve Locks
• Product Line: Melling Replacement Valve Locks
• Summit Racing Part Number: MEL-VL-200
• UPC: 729295201243
• Valve Stem Diameter (in.): 0.340 in.
• Valve Stem Diameter (mm): 8.64mm
• Lock Style: Stock
• Lock Groove Quantity: 1-groove
• Lock Material: Steel
• Manufacturing Process: Stamped
• Recessed for Lash Cap: No
• Quantity: Sold individually.

Pushrods

Pushrods come in a myriad of different lengths, for different engines, including custom length for you engine builders that need something special. Regarding quality, you’re looking at material, wall thickness, and tube diameter. That is, until you get into the $300+/set products.

Tube diameters vary from 5/16″ to 7/16″, and materials are typically steel and Chromoly steel. Wall thickness varies from 0.080″ to 0.125″, to 0.165″.

From Comp Cams:

Here is a Comp Cams ‘basic’ pushrod and one of their top-of-the-line products; they’re not for the same engine.

Hi-Tech 8.100″ Long, .080″ Wall, 5/16″ Diameter Pushrod – Single

Hi-Tech Dual Taper 7.400″ Long, .165″ Wall, 7/16″ Diameter Pushrod – Set of 16

Note the spec difference between these two pushrods. The first is 5/16″ in diameter, and the second is 7/16″. Well thickness of the first is 0.080″ while that of the second is 0.125″. The second part is also made from a higher quality material.

Rocker Arms

You might know that early V8 engines utilized shaft mounted rocker arms, and that it was Chevrolet, with their 265cid V8 in 1955 that introduced the world to stud mounted, stamped steel rocker arms. This allowed the reduction of manufacturing costs and aided the affordability of V8 engines in the 1950’s and their resultant explosion in popularity. Of course, some automakers were later than others in making this change, and the Chrysler company hemispherical and polyspherical engines still required rocker shafts.

I know that you already know what a V8 cam-in-valley setup looks like. I’d like to use this diagram to reinforce the concept that each and every component, camshaft, lifters, pushrods, rocker arms, rocker arm mounting, valve springs, spring retainers, and stem locks must be both compatible with one another and also designed for the service your engine is intended to provide.

You might think of it this way; there are 16 valves and 10 or so components per valve. So, there are some 160 parts, some of then not terribly expensive, where a fail in any single one of them will put you out of business.

Finally, if you look at this diagram and picture an OHC setup, with the large lifter, pushrod, and rocker arm unnecessary, it’s easy to understand how the valvetrain mass is greatly decreased. Remembering that the forces increase as the square of the velocity (2 x speed = 4 x force), you should be able to appreciate how an OHC engine just doesn’t have the high rpm challenges of a traditional 2-valve V8.

Ratios

You probably know that rocker arm ratios of pushrod lift to valve lift vary from 1:1.5 to 1:1.8. Most performance engines will be around 1.6, it seems. This is the ratio by which the cam lift will be multiplied, and that the valve experiences. If your cam has 0.500″ lift and you have 1.5 rocker arms, valve lift will then be 0.750″. Your valvetrain components, especially the springs, need to be able to accomodate this.

You definitely don’t want to go crazy here, by jumping willy-nilly to a higher ratio. Get expert advice, cross check it, and verify the other components involved. Also, be aware that additional lift doesn’t always provide substantial benefits. Many performance heads don’t provide much additional air flow at high valve lifts.

Flows at Higher Lifts

A word of explanation – The chart above shows “73.13%” as the first entry in the first “Change %” column. This reflects the change from 67 to 116. Likewise, the “102.63%” value is the change from 38 to 77.

This is the same RA III flow data as a graph.

It’s kind of interesting how the intake and exhaust graphs lie so close to each other. The .700″ lift adds almost 4% to the exhaust flow.

Hopefully this has illustrated the concept that huge valve lifts will not greatly benefit many heads. Huge lifts are the realm of really serious, huge port monster engines, by and large.

Some Rocker Arm Examples

As is the case with valvetrain components, higher rpms means beefier components throughout, and this certainly applies to rocker arms. The first step up over original equipment might be stamped steel arms with roller tips, along with stronger mounting studs.

Timing Chains

The single, in-block camshaft is almost always driven from a sprocket on the crankshaft, via a chain, to a sprocket on the camshaft that’s twice as big as the crank sprocket. The Chain is typically the ‘single-roller’ type. When rebuilding an engine, many people go to the double-roller type, although many knowledgeable resources view this as ‘acceptable overkill’.

OEM style chains tend to be the ‘silent chain’ variety; the name implies the benefit of this type of chain. These chains suffer more wear than the roller type chains and generate more heat. If you’re rebuilding an engine, put a good single roller chain (and sprockets) and call it good. You could also put on a double-roller set and no one would blame you. Plus, you could brag to your buddies about it.

Additional Resources

https://www.compcams.com/valve-train-geometry Comp Cams Valvetrain Geometry

https://www.bing.com/videos/riverview/relatedvideo?q=chevy+small+block+Timing+Chain+Installation&&view=riverview&mmscn=mtsc&mid=8F396F72697F4C3304698F396F72697F4C330469&&aps=14&FORM=VMSOVR Timing Chain Replacement for big-block Chevy

https://www.autozone.com/diy/ignition/how-to-do-an-engine-compression-test Compression Testing

Summary

The selection of cams and valvetrain components is complex, but there are lots of good resources. These include printed, online, and talking to experienced engine builders if one is available. This isn’t a good area for you to guess. Choosing the ‘wrong’ camshaft might disappoint you with its performance, but choosing the wrong springs or other component might end in disaster for your engine. Use your resources!