The Modern Camshaft
My last three entries were linked to articles that I thought were interesting. Together, they sort of created a camshaft time line. We learned a little about the early American development of the performance camshaft and the people and companies involved. We now know in today’s world, there is not a magic formula that can pick the perfect camshaft for the application. It seems the people that market these formulas do not have any reputation for being engine builders or have much experience running engine dynamometers (just thinking out loud). We also got a glimpse into the future where the mechanical camshaft and valve train will be non-existent. All this spans about 130-year period.
Cam profiles were initially shaped by hand with grinders, files, and abrasive materials. Models were created on paper with compasses, protractors, scales, and straight edges. The modern cam profile is designed using computers and software to run sophisticated mathematical equations until the desired valve motion is created. We now look at the early cam profile designs as crude and ridiculous compared to modern designs. The future valve actuated systems will make our modern cam profile designs also look crude and ridiculous.
The mechanical camshaft and valve train, as we know it, has reached its peak. We have squeezed out all of the performance that is going to be possible. Stronger, lighter, wear resistant, CNC machined components, larger base circle diameter lobes, larger follow wheel diameters, the best valve springs and systems without valve springs, multiple OHC systems, finger follower systems, variable cam timing systems, the best cam design software, and so on. It has all been done. If you think you are doing something new, you are probably only catching up with technology.
Even though the technology is here, many are not using it. The OEM world seems to be the most advanced. Look at the automobiles that can be bought today. Simply amazing! Power, efficiency, suspension, brakes, aerodynamics, electronics, and air conditioned. Much of the racing world is far behind in the available technology. That has not always been the case. It is all about money, I understand. It will be a very long time before the mechanical camshaft becomes obsolete. Until then, please keep me in mind for today’s modern cam profile designs.
Just In Case You Were Wondering
I enjoy reading about the history and development of things. Here is a good article on the beginnings of the automotive performance camshaft in America. It basically starts with Ed Winfield and the Ford Model T. In the beginning, Winfield and others modified existing stock camshafts. My question has always been…Who designed and ground the stock camshafts of the day? We never hear about those individuals.
Koenigsegg's Camshaft Free Engine
I look forward to this engine being perfected. I think it will bring a whole new perspective to the cam profile design world.
Cam Profile Design And Camshaft Design
These two phrases are sometimes used to mean the same thing. In reality, they are two separate processes, but both are important to produce a properly performing camshaft.
Cam profile design is my main focus. This is the actual designing process of the cam lobe. Most of the information in this blog section describes what is involved in designing a cam profile. Hopefully, you have read all of the posts so far, and have a good understanding about cam profile designs.
Camshaft design is different from cam profile design. Once the cam profiles are designed, the next step is to make the camshaft. Obviously, making the camshaft is much more involved. There are many stages in the camshaft manufacturing process. From the material to make the camshaft, heat-treating, indexing the lobes, gear cutting, machining and grinding equipment used, quality control, all the way through to the packaging to ship the finished camshaft. I’m sure you will be glad to hear, that I have no desire to describe in detail, the manufacturing process. It is easy enough to imagine all that is involved.
The part of camshaft design that most of you are interested in is, what camshaft do I need for my application? That will involve the choosing of the correct camshaft core, the proper profiles, lobe separation angle, and the camshaft indexing in relation to the crankshaft. All of these choices have to be correct, or the camshaft will not perform as well as it could. No doubt, a big task for the person picking the camshaft. If you find someone that can routinely choose the correct camshaft for the application, stick with that person. There are also software programs written to do this. From my experience, the programs that really work are expensive. They are marketed more towards a company than an individual.
As you can see, cam profile design and the camshaft design, must work together. You can have the best cam profiles, but if the camshaft design is poor, the camshaft does not perform well. The cam profile designs are blamed along with the camshaft and the manufacturer. You can also have cam profiles that are not correct for the application, but the camshaft design is good. The camshaft will generally perform ok, but not as well as it would with the proper cam profiles. This is the most common problem with camshafts today.
If you are new to my blog page, please start at the beginning and read all of my posts. You will have a better understanding of cam profiles and my approach to cam profile designs.
If the cam profile lift table is the same on the opening and closing side, the profile is symmetrical. If the lift table is not the same, the profile is asymmetrical. Simple enough…right? You must study and graph the lift table of any cam profile to truly understand the profile. The lift table is the blueprint of a cam profile.
Most of the early modern cam profile designs were symmetrical. When I speak of modern cam profiles, I mean a computer was used in the design process. Symmetrical profiles were easier to design and the knowledge available, at the time, was just in the beginning stages. Asymmetrical profiles were created when the opening and closing ramps became different. This is because the valve can be opened faster than it can be closed. Most cam profiles today are asymmetrical.
In most conventional cam profiles, the opening and closing ramps are what make the profile asymmetrical. This causes some of the main profile to also be asymmetrical. Usually from the end of the ramp to around .050 tappet lift, the profile will be asymmetrical. As you move up the lift table to maximum lift, the profile will become less asymmetrical. On either side of maximum lift, the profile will actually be symmetrical for many degrees. The major asymmetry is in the low lift areas of the profile. The higher lift areas may be asymmetrical, but not by very much. Again, the only reason the profile is asymmetrical, is that the opening and closing ramps are designed differently. There is no magic going on here to try and manipulate the air flow.
For an unconventional cam profile, the entire opening and closing side of the profile is intentionally designed different. This is because the rocker ratio is not consistent (as in a conventional profile) throughout the valve movement. Usually, you can see the different shape of the opening and closing side of the lobe. This type of profile is highly asymmetrical and must be designed that way for a smooth valve motion.
Conventional symmetrical cam profiles are still designed today. There is nothing wrong with them. Just because a cam profile is symmetrical, doesn’t mean that it is a poor design or inferior.
If you haven’t noticed, the website has a new domain name (web address).
This is a registered address that belongs to me. Having a registered address is more professional and it makes the website easier to find in search engines. It is just another ongoing development in the website. I created this website and constantly update and develop it myself. I am certainly not a professional website builder, but if you are someone wanting to build your own website, I would be glad to offer any help to you.
Be sure to update your bookmark to this new address. The system will automatically forward you from the old address until you change.
Check back, I will have a new technical post soon.
Adjusting Solid Lifters
It seems like each person has their own way of adjusting valve lash. As with hydraulic lifters, talked about in the previous post, there is nothing mysterious or complicated about adjusting the valve lash. The valve being adjusted must be fully closed. That is the only rule that matters. Whatever procedure you want to use is up to you. The content of this post will be about the lash itself and not the adjusting procedure.
Since the solid lifter does not have the ability to take-up the clearance created in the valve train, there will always be some running clearance in a hot engine. Most engines will gain clearance in the valve train from a cold to a hot engine. I’m sure there are exceptions, but I have not come across one. This gain in clearance is taken into consideration when designing the cam profile ramps for a particular engine combination. A cast iron push rod engine will not gain as much clearance as an all aluminum push rod engine. The ramps should be designed differently for each application. Many times a cam profile is used without any thought given to what the actual running lash was designed to be. The more lash, the less area the cam profile has. The opening and closing valve velocity points will also increase which could cause mechanical damage to the valve train. Less lash will increase the seat-to-seat duration, which may bleed-off cylinder pressure. Changing the rocker arm ratio also changes the lash setting. There is more to choosing the correct cam profile than just lift and duration numbers.
The valve lash settings come from the cam profile design. It is not just some number that is made up. The material of the engine block and heads, the rocker arm ratio that will be used, and the application, are all considered when designing the cam profile ramps. Older cam profiles were mostly designed for cast iron engines with 1.5 or 1.6 rocker ratios. Many engines today are all aluminum or have aluminum heads and higher rocker arm ratios. Again, the best performing cam profiles will be the ones that are designed specifically for your combination and application.
I will finish this post the same as the previous post. I know all kinds of combinations and lash adjustments are used for camshafts and lifters. I have already stated many times the disadvantages and dangers of mismatching cam profiles and lifters. I will just continue to shake my head and be amazed at why this is done.
Adjusting Hydraulic Lifters
Standard hydraulic lifters are designed to automatically compensate for any clearance that is created in the valve train from a cold engine to a hot operating engine. They will also compensate for any clearance that is created from wear or unintentional conditions. The lifter not following the cam profile is the most common unintentional condition. Lifter float or valve float is the more common term. This can be caused from not enough valve spring pressure, over revving the engine, or the wrong cam profile design. When this happens, the hydraulic lifter will “pump-up” to take up the temporary clearance created. Since the initial hydraulic lifter adjustment was set to operate at zero clearance, this extra “pump-up” of the lifter will keep the valve from fully closing until the lifter “bleeds-down” to its original setting. Until the lifter “bleeds-down”, that cylinder will obviously loose compression and power.
Special “anti-pump-up” hydraulic lifters are designed to keep the lifter from “pumping-up” during this condition. There is a strong snap ring retainer in the top of the lifter that stops the lifter plunger travel. The standard hydraulic lifter also has a retainer, but it is usually a weak round wire type. It is not designed to resist the plunger movement. The “anti-pump-up” lifters are adjusted differently than the standard lifters. Standard hydraulic lifters have around a 0.200 total plunger travel. I still do not understand why they are designed with that much travel. Certainly much more then will ever be necessary. Probably to compensate for the “stacking” tolerances (engine, head, pushrod, etc.) in production. The preload adjustment can be set anywhere in this travel range. Normally, the plunger preload adjustment is less than 0.050 when done by hand. All that is needed, is enough preload to compensate for any clearance that is created in the valve train from a cold engine to a hot operating engine and from any wear. In reality, on a cast iron stock engine, this would be less than 0.010. An all aluminum engine may require more. It always amazes me how some mystery is created when adjusting hydraulic lifters. Take a hydraulic lifter apart and analyze it. Look closely at the oil holes, oil channels, check valve, and envision how the oil flows. Make sure you understand how it works. Simple… right? Certainly, no mystery involved. I am referring to a stock OEM lifter here. Special “anti-pump-up” lifters operate the same way as stock ones. The plunger travel is only around 0.050 and they have that strong snap ring retainer. Adjustment is a little different. The idea is to preload the lifter so the plunger will just be touching the retaining ring during hot engine operation. This will prevent the lifter from “pumping-up” any further if valve float was to happen.
The retainer in the standard hydraulic lifter is not designed to resist the plunger travel, so the lifter should be preloaded enough to keep the plunger from touching the retainer during hot engine operation. The preload can be set anywhere within the plunger travel range. I guess this is where the mystery comes in. Usually you hear “quarter turn”, “half a turn” or “one full turn” on the rocker arm nut used to describe the preload adjustment. The plunger can also be adjusted where it is bottomed-out in the lifter. For engines without adjustable rocker arms, the pushrod length should preload the lifter at the midpoint of the plunger travel. All of these will work fine. Take your pick.
Cam profiles are designed a specific way to use a hydraulic lifter. I know all kinds of combinations and lash adjustments are used for camshafts and lifters. I have already stated in previous posts, the disadvantages and dangers of mismatching cam profiles and lifters. I will just continue to shake my head and be amazed at why this is done.
This is the new website for Ingram Engineering Cam Profile Designs. The old website service is being discontinued and that website will no longer be updated and will eventually be deleted. Be sure to change your bookmark to this new website address. The new service is much easier to use and has more features. Hopefully, everyone will like the results. Please leave a comment.
Unconventional Valve Trains
The majority of my cam profile designs are for conventional valve trains. Meaning the valve lift is a constant ratio compared to the cam profile lift. An example would be if the rocker arm ratio were 1.5 to 1, the valve lift would be the cam lobe lift multiplied by 1.5 at any point. Push rod engines with a rocker arm and overhead cam engines with a direct acting tappet are examples of a conventional valve train. Unconventional valve trains have a ratio that will vary through the valve movement or a cam lobe shape that is not typical. Overhead cam engines with finger followers are an example of a ratio that will vary. A Desmodromic valve train is also unconventional and very interesting. I would recommend studying this valve train. There are a few other older valve trains that are unconventional, but are not used in modern engines. They are still worth studying. You cannot fully understand something without knowing the history and its evolvement. Early internal combustion engines did not have an intake cam lobe and only used an exhaust lobe that opened at the bottom of the exhaust stroke and closed at the top. The intake valve used atmospheric pressure and a valve spring to open and close. To go from no intake cam to what we have today, is an interesting and educational journey.
Different cam profile design programs are written for the different valve train designs. Each program is costly and has to be justified based on the demand for certain profile designs. Much of the input data for these unconventional cam profile designs consists of angles and dimensions for that particular valve train. This data is usually not known and is not easily measured. Having the program only solves part of the problem. Usually a blueprint of that valve train is also necessary. Good luck getting that! Many times, if the customer can plot a ratio table of cam lift to valve lift in 1-degree increments, I can design a cam profile.
Like all of the posts, be sure to read the previous ones first.
I hope some of you participated and drew the lift curve in the previous post. For those that did, you will be further along in understanding cam profiles. If you haven’t already, play around with creating your own lift curves. There are many important observations that can be made by creating different lift curves.
An increase in the slope of the straight-line segment will increase the area of the profile. Once the lobe lift and the duration at 0.050 are chosen, the slope of this line will be the main difference between profiles with the same lift and 0.050 duration numbers. Would you intentionally design a cam profile with less area than what is possible? If you want less area, would it not be better to just design a cam profile that is smaller at 0.050 and/or less lift, but still with as much area as possible. Common sense will give you the answer. This is where you have to watch out for the marketing gimmicks.
Another observation is the length of the ramp area. The ramp area will be from 0.000 to 0.020. The valve contact point will fall somewhere in this range. This 0.020 can be divided-up into as many degrees as you would like, but after a certain length, it is just senseless to keep going. Around 20-degrees or less is plenty of room for any type of ramp design.
You will notice how the duration spread between 0.020 and 0.050 will set-up the slope for the lift curve. The terms high intensity and low intensity cam profiles are more of a marketing term, but relates to this spread. The closer the spread, the steeper the slope will be and more area will be created. This gives you more of a practical explanation without the marketing.
The top of the lift curve coming from maximum lift should be a nice, gentle curve. There should be no dwell at maximum lift and no corners blending into the straight-line segment of the lift curve. The lift curve from 0.050 to 0.020 to 0.000 should also be a nice, gentle curve. After you draw a few lift curves free handed, you will be able to see them in your mind and do it with your eyes closed. I know that cam profiles are sometimes designed with a dwell at maximum lift. These are special application profiles only and are not considered a good design.
Being able to look at a lift curve and seeing this information will be a big advantage when comparing cam profiles or analyzing a particular cam profile. It also takes something that seems very complicated and breaks it down into something simple and easy to understand.
Here is a simple exercise to start with. We are going to create a cam profile in the form of a lift curve chart. Draw a horizontal and a vertical line. These will be the “x” and “y” axis of the chart. The vertical line is the cam profile lift and the horizontal line is the degrees of rotation (duration). Zero is the point where both axis meet. This chart represents only the opening side of the cam profile. Next, plot the maximum lift of the profile. Now, plot the duration points at the following lifts: 0.020, 0.050, 0.100, 0.200, and 0.300. In the example, the maximum lift is 0.400. The plotted duration points are 68 (0.020), 60 (0.050), 52 (0.100), 39 (0.200), 26 (0.300). Remember, this is camshaft duration, not crankshaft. This is also only half of the cam profile, so the duration points are ¼ of the crankshaft duration. If this doesn’t make sense, think about it until it does. It will help to go back and study the posts on lift tables. From 0.020 to 0.000 will be the ramp area. The beginning of the ramp at 0.000 is 90-degrees. The chart should look like the one below. The plotted points show up as the red dots.
Now, with a smooth, gentle curve starting at 0.400, connect the plotted points down to 0.000 at 90-degrees. If you have been drawing along with your own chart, guess what? You have basically just created a cam profile and you didn’t even have to use any mathematical equations. Obviously, there is more to designing a cam profile then just this, but this is a legitimate profile with good area that would perform well if manufactured. If you haven't been playing along, you can take a short cut and print the chart.
Now, let’s analyze the lift chart closer. Notice the curve you drew connecting the plotted points is straight between 0.300 and 0.100. Depending on the profile lift, this straight segment will be shorter or longer in length. There will always be a straight segment in a good profile design. This straight segment has a slope to it, right? Maybe around 50-degrees with the horizontal axis. As the slope of this line increases, the area will also increase. The velocity and acceleration numbers will also increase. At some point, the slope of this line will be at maximum for the profile. When this maximum slope is reached, the cam profile is what I call “maxed out”. Basically, all of the area has been designed into the profile, within the limitations. It would be difficult to “better” this type of profile. Trying to make the profile smoother would be the only possible outcome.
I create a lift chart many times, as the first step in designing a cam profile. Especially, if a customer is giving me durations at different tappet heights. I will know right away, by the slope of the straight-line segment, if the cam profile will even be possible. I will usually plot duration points at 0.020, 0.050, and then at every 0.100 lift interval. From 0.020 down to 0.000 is the ramp area. The length of the ramp is usually around 20-degrees. In the example, the ramp length is actually 22-degrees. A good modern solid or hydraulic ramp can be designed with 20-degrees or less of length. You can see in the chart, a longer ramp will serve no purpose. It only keeps the valve separated from its seat for a longer period of time. No advantage. There is no significant airflow in this area. The area under the lift curve is that area inside the curve drawn to connect the plotted points. It is easy to see how changing the curve, changes the area. The area to increase for better performance is that above 0.050. Not below.
Usually, a cam profile concept starts with a maximum lift and the duration at 0.050. From there, the duration at 0.020 is around 30-degrees bigger than at 0.050. That spread determines the high and low intensity profiles that you hear talked about. You can see on the chart how the 0.020 and 0.050 durations will setup the slope for the straight-line segment.
Much can be learned from the cam profile lift chart. Whether from an existing profile or the design of a new one. The lift chart is essentially the cam profile.
Cam Profiles And Marketing
It is difficult to find practical information on cam profiles. Mostly, all kinds of mathematical formulas and equations will show up when searching cam profile designs. The math doesn’t really tell you anything about the cam profiles. I try to give sincere, practical information about designing cam profiles in these blog entries. If you read and understand all of the entries so far, you will have a solid foundation of knowledge on the subject. Certainly more than the average engine person.
I cannot imagine anyone designing cam profiles today that does not use a computer. The computer does all the math that I mentioned earlier. A person still has to create the profile and determine if it is the proper profile for the application. That type of knowledge is difficult (if not impossible) to find. Mostly, it comes from many years of experience. It is not common knowledge and is not an exact science like the mathematical part is.
The marketing of cam profiles is usually directed toward the application side. Some marketing is occasionally directed at the mathematical techniques that are used to design the cam profile. As the average engine person becomes more knowledgeable and has access to more technical equipment, the less the marketing gimmicks work.
While I was at Reed Cams, I was able to profile every camshaft that I could. Before we had a computer profiler, I would use a manual one. We kept pages and pages of cam profiles for reference. Later, we kept files and files stored in the computer. Basically, all this data was knowledge to me. It showed me different design techniques and was a good way to compare profiles from different manufacturers. After you see a certain number of cam profiles, the marketing gimmicks are ignored.
I would say that anyone in the business of designing cam profiles today could create a good profile. It is rare to see a “bad” profile designed today using computers. Some profiles will certainly make more power than others and some profiles will create more stress on the valve train than others. The problem is that new cam profiles are not used. Older profiles, improper profiles, and copied profiles are still used way too often. See the last blog entry.
Keep reading my blog, ask questions, expand your knowledge, and don't let the marketing gimmicks be what guides you.
It’s 2015, but for the typical engine builder and racer, much of the same stuff is still going on that I remember happening twenty years ago or even longer. Hydraulic lifters are run on solid cam profiles, solid lifters are run on hydraulic cam profiles, valve lash is set with no regard to the cam profile design, camshaft grinders are still copying lobe profiles, base circle diameters are ground to any size with no regard to the original profile design, roller cam profiles are not designed for the roller wheel diameter used, and on and on. All of the stuff that ticked me off years ago is still going on. It’s sad.
With CNC cam grinding, machining, and head porting being common today, I would think these types of tactics with camshafts would be gone by now. Much of the blame should go to the racing engine rules that have to be dealt with. Hey…NASCAR is finally allowing roller camshafts in the Cup engines this year. WOW!
Performance cam profile designs are mostly defined by the engine design and the materials of the day. The end user’s perception, whether right or wrong, also plays a part. I have many cam profile design ideas (as do other cam profile designers) that are just not applicable to today’s racing engines or what the market wants.
In the OEM production world, I am glad to see roller camshafts in push rod engines, multiple valve overhead cam engines, turbo and super chargers used, and electronic engine management systems that allow each cylinder to be tuned separately. Production engines are far more technically advanced than the typical racing engine in this country. Racing engines will still have a mechanical valve train long after production engines are computer controlled. Fortunately, that is good for the camshaft industry. Let’s just match the proper cam profiles with the camshaft and the application, as it should be.
Area Under The Lift Curve
You hear the term “area under the lift curve“ used a lot in cam profile designs. Above is a very simple chart to help visualize what is meant by the area under the lift curve. I created a very basic chart with a drawing program. It does not represent any known cam profiles and is not to any scale or resolution. Its only purpose is a visual aid.
Remember the lift table from previous posts? It shows the profile lift for each degree of rotation with zero-degrees being the maximum lift. If you convert the lift table into a graph form, you have the lift curve. The horizontal line is the number of degrees in the profile and the vertical line is the profile lift. The chart only shows the opening side of the profiles. There are two cam profiles represented in the chart; both have the same lift and the same seat-to-seat durations. The blue is the area under the lift curve. Simple enough, right? There is obviously less blue area under the black line than there is under the blue line. Once the valve starts to open, there is more duration for the same lift on the blue profile. Instead of the seat-to-seat durations being the same, the two profiles could have the same duration at .050 or any other tappet height. This is a very meaningful way to compare cam profiles and to see the advantage of having more area under the lift curve.
Cam Profile Questions
If you came into this not knowing much about cam profiles, you should now have a better understanding having read all of my blog posts up to this point. If you do not understand something or have any questions, please do not hesitate to ask. Send me an email at firstname.lastname@example.org.
I usually get my ideas on topics from questions or from discussions on the forums I follow on the Internet. I try to post at least one entry during the month. If you are not seeing a new post, it means I need your help coming up with a new topic.
I am not going to write about the history of the internal combustion engine. There is already plenty written on the subject. For those that are interested in this early history and the beginnings of the motorized vehicle, I would do some reading on the following to get started:
De Dion-Bouton (company)
I enjoy reading about the early days and development of the internal combustion engine, the automobile, and the motorcycle. The above recommended topics will certainly open the door to an interesting time in history. In your studies, you will find that the camshaft did not play a very important role in the early engines.
Some Early Cam Profile Developers:
Pierre Louis Bertrand
Maximum Lift And Centerlines
I listened to a discussion the other day about maximum lift and centerlines. I honestly have never given it much thought and have always used the two terms interchangeably. After listening to the discussion closely and sifting through the facts, I came away with a different perspective.
When I talk about the intake or exhaust centerline, I am referring to the maximum lift point. On a symmetrical cam profile, they are one in the same. The confusion begins, when talking about an asymmetrical cam profile. The centerline and the maximum lift will be different on an asymmetrical profile. It all comes down to the definition of centerline.
One side of an asymmetrical cam profile has more total degrees than the other side. If zero degree is the maximum lift, then by definition, the centerline will not go through zero and the center point of the base circle. To divide the profile into equal opening and closing degrees, the centerline will need to be off from zero by half the amount of the asymmetry.
I do not have a picture, so I will try to explain this with words only. Drawing a picture would probably make this easier to understand. The opening side of a cam profile is 100- degrees. Maximum lift starts at zero and counts down the profile to the beginning of the opening ramp. This is the lift table, which has been talked about many times before. The closing side is 110-degrees. Maximum lift starts at zero and counts down the profile to the end of the closing ramp. The asymmetry of the profile is 10-degrees. A line drawn through the center of the base circle diameter and zero (maximum lift) would not divide the profile into equal degrees. The line would need to pass through a point 5-degrees to the left of zero (opening side) to be the true definition of centerline. The centerline would then divide the profile equally into 105-degrees on each side.
A camshaft grinder can use whatever method to create the specifications for his timing card. He can also make-up any method he chooses. The maximum lift is generally used for the reference point in my experience. The lobe separation angle on a camshaft is the angle between the intake and exhaust lobe maximum lift points. It only makes sense to use the maximum lift as the reference point for indexing the camshaft in the engine. When camshaft cores are made, the maximum lift is used to index the lobes with the dowel pin or keyway. When programming a cam profile into a CNC machine, the maximum lift is used as the reference point.
All of this is really no big deal. It is more of an argument over the true definition of centerline than anything else. I have always (and will continue to do so) used the maximum lift of the cam profile for a reference point. I have also unknowingly used the term centerline to mean the maximum lift. From now on, I will stop using the term “centerline”, and only use “maximum lift” in any camshaft discussions. That should eliminate any confusion.
The first thing that comes to mind when one thinks about a cam profile is the actual shape of the lobe. In the cam profile design world, the lift table is the cam profile, not the shape of it. The actual cam profile shape (excluding the physical dimensions) is of little importance.
As talked about in previous blogs, the lift table shows the tappet height at each degree of cam profile rotation. There is also a sample lift table shown in a previous blog. What may not be clear to some is that the lift table does not represent any particular type of tappet. The table only shows tappet height. The lift table could be exactly the same whether the tappet was a roller or a flat style. The table could also be the same no matter the diameter of the tappet or roller wheel. Sound confusing? It’s really not.
The cam profile shape is created by the lift table and the tappet used. As long as it is physically possible, any tappet can be used with any lift table. Using the same lift table, the type of tappet will determine the shape of the cam profile. Obviously, a roller profile and a flat profile will look different, but the valve movement will be exactly the same. The tappet height at each degree of rotation will be the same. The lobe shape combined with a particular tappet will determine the tappet height. Make sense now?
Many times a flat profile cannot be made from the same lift table as a roller profile, because the velocity will be too high for the diameter of the flat tappet face. A roller profile might encounter a severe negative radius when made from the lift table of a flat profile. Make sure you have read and understand all of the previous blogs if this is not making sense. If none of these or any other physical problems occurs, the same lift table can be used to produce a flat and a roller cam profile. The finished cam profile would still need to comply with all of the other design parameters to be a good profile.
To sum it up, the profile design procedure will create the lift table. Based on the type of tappet that will be used, the cam profile shape is then created and the final design is accepted after much trial and error until all of the parameters are met. Computer software allows all of this to happen very quickly even though separate steps are actually taking place.
Valve Contact Points
Valve contact is the term I have always used to describe the point on the opening side of the cam profile where the valve first starts to move. On the closing side, this point is where the valve first makes contact with the seat. These points are on all cam profiles, both solid and hydraulic. I do not think this is an official cam design term, as I have heard other terms used.
The valve contact point is used when designing the cam profile ramps. On a solid cam profile, the valve lash will be determined by where the valve contact points are and the rocker arm ratio used. Some cam profiles are designed without much attention given to the ramps and the valve contact points. The valve contact and the lash is decided on after the cam profile is designed. I do not do this. I design the ramps first, based on the type of cam profile and the application. I then design the cam profile and mate it to the opening and closing ramps. On both a solid and a hydraulic cam profile, the valve contact points will determine the velocity at which the valve will open off and close on its seat. The proper location of the valve contact points will contribute to a smooth and reliable valve train for the application.
It has been a little over a year since I created this website and I am starting my fifth year in business next month. I just want to thank everyone that has supported me and those that have given me the opportunity to design your cam profiles.
Valve Timing Program
I have created a simple, handy, spreadsheet file that will calculate the valve timing events for symmetrical and asymmetrical cam profiles. It will also give valve lift and valve lash data along with the minimum flat lifter diameter based on the maximum velocity. It will run with any version of Microsoft Excel. The file can be purchased on the "ORDER" page.
Cam Profile Design Limitations
I would recommend reading the previous entries before starting here. I have intentionally not explained in detail what some things are, since I have already done so in the previous entries.
Every design method has the same limitations to deal with when designing a cam profile. These limitations will make it difficult to prove which method is better.
A flat tappet profile has a velocity and a nose radius limit. The tappet diameter alone will determine the maximum velocity that can be designed into the profile. The nose radius is determined by a combination of the base circle diameter, lift, and nose acceleration.
A roller tappet profile has a pressure angle and a negative radius limit. The pressure angle is the angle between where the lobe and roller wheel make contact. It is mostly determined by a combination of the base circle diameter, roller wheel diameter, and the lift. The negative radius is the concave area on the opening and/or closing flank of the profile. It is determined by a combination of the base circle diameter, lift, acceleration and roller wheel diameter.
Now you can see the importance of a large base circle diameter and roller wheel diameter when designing a cam profile. That is the reason for the trend to the larger camshaft journals. Strength is also a factor.
All of these limitations can cause premature wear and mechanical damage to the valve train if they are exceeded far enough.
Fortunately, there are some design "tricks" that can help deal with these limitations. On some flat tappet profiles, the maximum velocity can be dwelled (DMV) for a certain number of degrees, to increase the lift and duration without causing a sharp nose radius. This will not work for all flat tappet profiles. There are some profiles that just cannot be made. For example, design me a cam profile for the following: Small Block Chevy 1.8685 journal diameter, 0.842 OEM flat tappet, 240-degrees at 0.050 tappet height, 0.400 lobe lift. Sounds simple enough, right? Please send me the basic lift table when you are finished. You will become my new best friend. Thank you in advance. A technique can be applied to roller tappet profiles that will dwell the radius of curvature for a certain number of degrees. This will keep the maximum acceleration from going too high and creating too small of a negative radius. An acceleration curve chart will immediately reveal if one of these techniques was used to design the cam profile.
(a little secret) As long as there are limitations, all cam designers will eventually end up with basically the same cam profile design, for a given application. Some designers will just spend more time on their designs to make them the best that is possible within these limitations.
This is part 3 on this topic. Go back and start at part 1. Below is a typical cam profile lift table. The lift table is really what a cam profile is all about. The actual shape of the lobe will be determined by this lift table and the tappet that is used. This shows only the opening side of the lift table. The table shows the tappet height at that degree of lobe rotation. Zero degree is the maximum lift point. Ninety-four degrees is the beginning point. Sort of the opposite of what you would think, but this is the correct layout and will make sense later.
From the lift table, the velocity, acceleration, and jerk tables can be calculated. Each of the four tables can then be graphed to give a visual chart that is easier to look at and interpret. The acceleration graph is what gets the most attention. The acceleration curve chart on the home page was created from this lift table. All of the four tables and charts show valuable information, but the lift table is the one used to make the cam profile.
Like many things, people know how to do something, but do not understand why. I always want to know why. All of us know the common duration at 0.050 camshaft specification. It is accepted without much thought of why or where is really comes from. Do you know the duration at 0.050 from this lift table? If you look down the lift column, find the closest number to 0.050. It is 0.0502788. The degree related to this number is 66. That means at 66-degrees from maximum lift the tappet lift is 0.0502788. The exact degree for 0.050 would be 66.06 from linear interpolation. Now you see why the lift table layout is this way. All of the valve timing figures are based off of maximum lift. If the closing side of this profile were the same, 66.06 would also be the degree that 0.050 tappet lift takes place. If the closing side is different (asymmetrical), the degree may be some other number. Adding these opening and closing degrees at 0.050 tappet lift equals the duration in camshaft degrees. For crankshaft degrees, which is what is published, multiply camshaft degrees by two. Remember, the crankshaft rotates twice as fast as the camshaft. These numbers will also be used to calculate the opening and closing points for the valve timing. That is why for an asymmetrical cam profile, these numbers from the lift table must be known. Now you know why.