I started reading Billy Godbold's new book today. I would definitely recommend everyone interested in this stuff to read this book.
Cam Profile Rate
Sometimes fast rate, slow rate, or aggressive might be the term used. Like most camshaft terms, they are used in marketing to sell camshafts. What makes a cam profile fast rate or slow rate? What makes a cam profile aggressive? Sometimes the term only applies to the profile ramps, such as the ramps are fast or the ramps are slow, the ramps are aggressive.
If you look at enough cam profiles, some definitely move the valve faster than others. Basically the movement of the valve (or tappet) per degree of lobe rotation is considered the cam profile rate. Velocity is the actual term used when designing cam profiles. In flat tappet profiles the maximum velocity is determined by the tappet face diameter. Roller profiles will usually have a faster maximum velocity and most are about the same for a specific profile.
Some ramps will open the valve faster, some ramps will close the valve slower. It's just all part of the design. If someone is trying to sell you a camshaft that has fast ramps then slow ramps are bad. If the maximum velocity is higher then it is better. Sound familiar. If you give-in to this type of marketing, read my last post. Maybe read it a few times, it is very short and to the point.
The best way to compare cam profile rates is by looking at the duration at the higher lifts. There is a reason most camshaft manufacturers do not publish duration figures past 0.050 tappet lift. Measure the duration at 0.100 intervals. Compare the duration numbers. If the camshafts are the same at 0.050 but one is larger at 0.100, 0.200, 0.300, and so on, the larger one has a faster rate. More importantly, it has a faster rate where is really matters. The faster rate at the higher lifts gives you more area under the lift curve. What goes on above 0.050 on a cam profile is a whole lot more important than what goes on below 0.050 as far as making power.
In a four stroke internal combustion engine turning 6000 rpm the valves are opening and closing 50 times a second. At 10,000 rpm that number increases to 83 times a second. Don't overthink this stuff or pay much attention to the latest marketing gimmicks.
Why 0.00000001 Resolution?
My understanding is the best CNC machines are accurate out to five decimal places. I saw some numbers like 0.00007. When we use to cut lobe models on manual milling machines we were able to go out to five decimal places using a dial indicator. The fifth decimal place was a "precise estimate" from the operator.
You might wonder why do cam profile lift tables go out to eight decimal places since the best machines are only good to five decimal places? The eight decimal places are necessary to create a smooth velocity, acceleration, and jerk curve for the cam profile. With five decimal places the curves are very jagged and hard to analyze. The lift curve is really the only curve that will work with five decimal places but to properly design a cam profile, smooth velocity, acceleration, and jerk curves are necessary.
Since the cam profile is designed to eight decimal places and only machined to five decimal places the finished lobe profile is not exactly the same as the design, close but not exactly the same. The old manually made lobe models were even farther away from the design but still worked just fine.
I use this saying all the time: "There are three cam profiles, (1) the original design, (2) the finished lobe, and (3) the cam profile in a running engine." All three are different. Don't get caught-up in worrying about numbers being exact.
I appreciate the comments received on my posts. I now receive more spam than actual comments so I have disabled the comment feature. I may enable it again in the future to see how things go. Please send me an email or call with any suggestions or comments you have. Thank you.
Creating A Cam Profile
What actually is the cam profile? In the beginning, the 3-arc type cam profile was a lobe shape that had some dimensions on it like a blueprint. You could then physically machine the cam lobe shape from the dimensions. Anyone can create a cam profile this way. The only thing you know for sure about the finished cam profile is the maximum lift. None of the other data will be known until the cam profile is actually made and then measured. Changing the dimensions of the arcs will change the measured data. The 3 arcs are the (1) base circle diameter, (2) the nose(tip) radius, and the (3) flank(side) radius. The distance between the base circle and the nose will obviously determined the maximum lift. The lift of the tappet at various places is measured out to four decimal places and the duration and velocity data is then calculated. That will provide enough data to know if the profile will work for the application. As the need for more control over the cam profile increased the number of arcs also increased. I am not sure but it looks like six different arcs were eventually used. That allowed some type of ramps to be integrated into the profile. An overall slow process but it worked. Remember a low rpm engine with light valve spring pressure is very forgiving to the cam profile design. This was all done before computers and involved mathematical equations were used to design the cam profile.
With computers a cam profile lift table can be created out to at least six decimal places. This lift table IS THE CAM PROFILE and can tell you almost everything you need to know. You just have to know how to read it. Below is a sample lift table on the opening side of a cam profile. There will also be one for the closing side. In this example they are the same (symmetrical cam profile).
The table lists the tappet lift at each degree of camshaft rotation. The first column is the degree of rotation and the second column is the tappet lift. Zero degree is the maximum lift of the cam profile. Do you know the duration at 0.050 for this profile? If you don't, you need to start at the beginning and carefully read all of my entries. The change in lift from one degree to the next is velocity. The change in velocity is acceleration. The change in acceleration is jerk. All these are important parameters to look at when analyzing a cam profile. A lift table with a resolution of at least six decimal places is necessary to adequately analyze these parameters. The lift table can be inserted into a spreadsheet program and these numbers can be calculated. A graph(curve) can then be created from these numbers. Lift, velocity, acceleration, and jerk curves can tell much about the cam profile design. If you have a computer camshaft lobe profiler or looked at a profile report, this is the kind of data you will see. Many engine builders use this data to help decide on which camshaft to use. The ramp designs and valve lash settings can also be analyzed. I also like to know the radius of curvature data and pressure angle data. That data is not always part of the lift table but should be available in the profile report.
As I said, the lift table is the cam profile. The lift table is the piece of data that you want to have. It will be able to tell you important information about the cam profile along with the ability to actually manufacture it. How the lift table is created is really not important. There are different ways the lift table can be created. The 3-arc cam profile talked about earlier could be computer profiled and the lift table created. Different cam profile design programs can create the lift table. The type of program used does not matter. On valve trains with a variable rocker ratio the valve lift data is designed first and then converted to the lobe lift table. The original cam profile design or an actual lobe should have a lift table that can be analyzed to determine if the cam profile design is a good one or a not so good one.
If you have a lift table that you would like analyzed, email it to me and I will give you my honest opinion on the cam profile design.
The answer to the duration at 0.050 question is 264.232 degrees at the crankshaft.
Cam Profile Design Program
Continuing on the subject of cam profile design, I have listed an early MS-DOS cam profile design program for sale on the "ORDER" page. Hopefully it can help those that want to continue learning and understanding about automotive cam profile design. It is a multiple part program consisting of a ramp design program, a profile design program, and a program that combines the opening and closing ramps and profiles to create the finished cam profile design. There is another program that will display and print the profile lift table data and another program to test the monitor for displaying graphs. These programs were written in the 1980's for John Reed by Vantur Electronics, Inc. in Atlanta, Georgia. Larry A. Turner was the computer genius who wrote the programs and was a friend of John's. The programs were revised over the years with these being the last version. Reed Cams, Inc. was a major sponsor of NASCAR in the 1980's. Many of the cars were running a Reed camshaft and also a Reed carburetor. The camshaft profiles being used at the time were all designed by this software. This is an affordable program that will allow you to actually design a performance cam profile that can be manufactured. Ships U.S. Priority Mail on 3.5" disc or compact disc. Contact me for more information if you are interested in the program.
The Math Of Cam Profile Design
For those interested in the mathematical equations of cam profile design this post is for you. I remember searching the internet for information on cam profile design and only being able to find information on the mathematics involved. This was not really what I was interested in so I started "Cam Talk" to help others interested in cam profile design and pass on more practical knowledge. As I have said many times before the software does the math for you. It does not teach anything about cam profile designs. That information seems to be very difficult to find.
These videos get into the math involved in designing a cam profile. I thought the instructor did an excellent job of presenting this. Here is a link to the beginning of the series to get you started. This stuff is not that interesting to me and I am certainly no mathematician but it is part of the process. Like I said, that's what the software does. Some do enjoy the math so this is for you.
Cam Profile Designer... part 2
I wanted to add this since my previous post sounded like I did not want to teach how to design a cam profile. I just do not think I have the ability to do so. Each camshaft application has its own limitations on cam profiles. I am certainly not an expert on every application (not even one). That comes from years of experience working with each particular application. You learn from trial and error on how far you can push the limitations. It is difficult to teach that especially if you do not know the limitations. Limitations tend to also change as valve train materials become lighter and stronger.
I have no problem sharing knowledge. That is why I write these posts. If you are someone that has a cam design program and has a specific question, I will be glad to answer it if I can. Trying to learn about cam design without actually doing it is difficult to do. Sort of like learning to ride a motorcycle without actually riding it. There is much to learn about cam profiles without knowing how to design one. That is what I really try to do here on Cam Talk.
Cam Profile Designer... part 1
If you have really read each one of my posts and halfway comprehended them, you should have a pretty good foundation about cam profiles. You should certainly have more knowledge than most people. Unfortunately you still do not know how to design a cam profile. I don't think I can teach you that. I don't think anyone can actually teach you that. Harvey Crane (of Crane Cams) had a class that he offered. He is the only one I know of that has done that.
There are many applications for designing a cam profile. We only think about engines and camshafts. Most applications are in the industrial world and have nothing to do with engines and camshafts. We never think about that world and they never think about our world (engines and camshafts). They are two totally different applications. The same math is used in both applications. That's why it is so hard to find information on specifically automotive cam profile designs. It's actually a small percentage of cam profile applications and not many people do it. Most of the information is focused on the math involved in designing an industrial cam profile (the shape). Again, the same math is used to design an automotive cam profile, the application doesn't matter. Any mathematician can design an industrial cam profile. He can not design an automotive cam lobe unless he has more knowledge than just the math. The engine camshaft profile has many unique rules and limitations that are not encountered in the industrial world. All that is stuff the mathematician will need to learn for the engine and camshaft world. That is the stuff that is hard to teach. Most mathematicians have never designed an automotive camshaft profile and never will, but they are all over the internet telling us how it should be done.
The computer software does the math part for you. You can teach someone how to use the software. The software does not know a good profile from a bad profile. The person using the software has to know that. That is hard to teach. It basically comes from years of experience.
You are an automotive cam profile designer once you have designed many cam profiles, had camshafts manufactured with your cam profile designs, run the camshaft in an actual engine, and made good power and reliability for the applications the profiles were designed for. One last thing, someone needs to pay you for your cam profile designs. In reality, there are very few of us.
Inverted flank is another cam profile term that you may not have heard of or understand. Like most camshaft terms it is used as a marketing tool to sell camshafts.
Inverted flank profiles are roller cam profiles that have a negative radius or concave shape on the side (flank) of the profile. Kind of like a dip in the road. Depending on the severity of the dip, it may not cause a problem or it may cause a big problem. These are only on roller profiles, not flat tappet profiles.
When lift is increased for a given cam profile, velocity and acceleration also increases. Duration will stay the same but the distance to travel is farther. This obviously causes the tappet to have to move faster. In a flat tappet profile the natural design tendency will end up with a smaller radius at the nose of the lobe. This is a limitation. The nose radius can only be so small. The velocity will also become too fast for the diameter of the tappet face. Another limitation. In a roller tappet profile the natural design tendency will end up with a negative radius in the flank (or flanks) of the profile. A limitation caused from the acceleration increasing.
There are techniques that can be used for both flat tappet and roller profiles that will help the designer control these limitations. Some designers use them, some do not. For those that do not their cam profiles will be limited in area or they end up being very rough and maybe damaging to the valve train.
The flat tappet profile limitations are pretty straight forward. You end up with a cam profile that has a sharp nose and runs off the edge of the tappet face if the limitations are ignored and not controlled. The roller tappet profile will eventually have a negative radius (the dip in the road) that is just too small to actually grind. The standard grinding wheel diameter on a camshaft grinder is 18-inches. That will have a 9-inch radius. It is possible to get smaller grinding wheels. Having ground camshafts for many years, I know this is a real pain to do. Grinding slightly inverted profiles is still a pain even with the standard 18-inch wheel. It really slows down the process and the camshafts usually cost more. The customer may not be too concerned about this, he wants to know if they will make more power. The answer is no. More times than not they are much harder on the valve train. Remember the dip in the road. A smooth road is much easier to drive on. Slightly inverted cam profiles may not be as hard on the valve train but they are still a pain to grind and there is no advantage in performance. Some of the camshaft marketing will try to tell you different. Using the proper software and techniques to design a non-inverted roller profile will always produce a better cam profile.
Modern Camshaft Technology
The hunt for the perfect camshaft is still alive and well.
Happy New Year
The beginning of another new year and a new decade. Time has a way of quickly passing by. Maybe it's just me. This will be the eleventh year for the website. Thanks again to my customers and anyone who has given me support through the years. Let me know what subject matter you would like to cover and I will be glad to post whatever I know about it or give my opinion. I have an opinion about everything. If you are new to "cam talk" please start at the beginning and read all of the posts. If you have questions, ask away. If you want to know more about a subject, let me know. I have no problem sharing knowledge. Have a prosperous new year.
Hello... still waiting on ideas for a new post. Call or email. Thank you for your input.
Happy New Year
Thank you to everyone who has contacted me or done business with me in the past. Hopefully I was helpful and the cam profiles are working well for you. If not, be sure to let me know and I will fix that. Have a prosperous new year.
Valve Train Component Failures
I am sure I will not have many racers agree with me on this post. We would joke around about asking the customer what he was doing when a component failed. The customer would reply "racing" and we would answer “well, there’s your problem”. Not that funny to the customer with broken parts, I guess. My point is racing is hard on parts. Most would agree on that.
Years ago, racing valve train components had many problems. Valve springs were manufactured with inferior steel and camshafts were bad copies of other camshafts. Some cam profiles had been copied many times, so the errors just added up. The combination of these camshafts and springs in a racing engine was a problem waiting to happen. The quality of flat tappet lifters was inconsistent. The crown and edge chamfer on the lifter face was the problem. This would sometimes cause the camshaft lobe to wear and of course the camshaft grinder was blamed. Roller lifters also had their problems. Especially when used on small base circle camshafts. This creates too high of a pressure angle. Unfortunately, it is still a problem today. Pushrods were tubes with ball ends welded on. Not very strong. Roller rocker arms were fairly decent, but still had their share of problems.
Today, the quality of components is the best they have ever been. There is junk out there and that is what you must avoid. If you are going racing, any racing, you better buy the best parts that are available. Many racers do not do this. Racing is an addiction, just like drugs. Many do it even though they can not afford it. This causes them to buy the junk parts or parts that are not as strong as they need to be for the application. The results are obvious, broken parts.
Sometimes a particular rule will force the racer to use components not up to the task. Unless you ignore the rule, the results are broken parts. All components wear out and break. They must be replaced before this happens. This can get expensive, so many do not do it. The results are broken parts. If components are continually failing, there is more than likely a problem on your end, not the components.
If you want to get in to this sport, realize it will take all your money and may not give you anything in return. Just as bad or worse than that pretty girl at the mall. There should be some kind of agreement to sign in order to be a racer. That may stop some of the whining. If money is a problem, do not get in this sport. If you do anyway, accept the consequences. As the saying goes “the truth hurts”.
In summary, parts are high quality today. If they are used correctly and in the environment they were designed for, the chances of having a failure are low. They must also be replaced on some type of schedule. Always analyze what you are doing before immediately blaming the part.
If you send me an email or leave a voice mail and do not receive a response, there is a problem some where. I will always reply. I will usually reply within a few hours or certainly the next day. There is no telling what the problem might be, so please try again. Make sure your email address is correct. Make sure your phone number is correct. My phone does not receive or send text messages. Do not send me a text message. Please use email or voice phone. Thank you.
Dynamic Compression Ratio
The dynamic compression ratio is calculated based on the intake valve closing point. I use 0.020 tappet height as the closing point. Some people use 0.000, 0.001, 0.005, 0.010, 0.050, or 0.053 for Harley-Davidson camshafts. As long as you are consistent and become familiar with the results, I do not think the exact height matters.
The dynamic compression ratio is calculated the same way as the static compression ratio. The volume in the cylinder when the intake valve closes is used instead of the full volume of the cylinder when the piston is at bottom dead center (BDC) is the difference. To find the location of the piston in the cylinder when the intake valve closes will take some involved math if done by hand. Like everything else done today that involves calculations, software and a computer is used. The location of the piston is determined by the stroke of the crankshaft and the connecting rod length. A profile report of the camshaft or a degree wheel and dial indicator will be necessary to find the degree of crankshaft rotation for the particular tappet height you have chosen. A program on the internet can probably be found to do the calculations for you.
Once you have the piston location (actually it will be the center of the small end of the connecting rod) the volume of the cylinder can be calculated. The compression height of the piston will need to be added in for the actual top of the piston location. Any dish or humps on the piston top will also need to be added in just like static compression ratio calculations. The dynamic compression ratio will obviously be less than the static ratio. How much less will have a large impact on the performance of your engine.
The dynamic compression ratio will be a more realistic number to use when choosing a camshaft. The importance of the intake valve closing point can now be seen. Use this next time you are changing camshafts. It could make a big difference in a good way.
Don't forget, keep sending suggestions for more topics.
I will be increasing my cam profile design cost for the first time. Not much, $8 increase for each standard cam profile design. It will help cover my increasing costs. This should be good for the next ten years. Thank you to everyone who has trusted me to design your cam profiles. Have a prosperous new year.
revised 12-22-2017... Hopefully I have some dedicated readers that follow these posts. I am going to leave it up to you to pick the subject matter for the next several entries. I am honestly running out of topics and this will assure me that the subject matter will be of interest. I do not want to write about topics that are of no interest and I do not want to repeat the same information that has already been posted. I spend a lot of time on these posts with the purpose of helping those interested in this stuff. Please speak up and send an email or call me. I look forward to your suggestions.
New Camshaft Technology
A better title would be non-camshaft technology. I believe this is the future of camshaft technology. The technology appears to be there but like anything new, the costs are high. Like most modern advances in the internal combustion engine, efficiency is the driving factor. This technology will be standard for passenger cars long before it is common in racing engines. The same as the electronic fuel injection and engine management technology. Today, the production car technology filters down to the racing industry. Funny how things change. https://www.youtube.com/watch?v=FJXgKY2O4po
If you are someone that has just acquired a camshaft grinder, you might be thinking about what to do next. I will leave it up to you how to run the business end. After that part is figured out, making a camshaft usually comes next.
I will use a small one-person shop with a manually operated Berco or Van Norman camshaft grinder for my example. I will also assume there are no finished master plates with the latest cam profiles. It does not take long to realize that your camshaft grinder is a nice conversation piece, but has no ability to make a camshaft.
Making some master plates is the first priority. Copying profiles from other camshafts is one route to take. Having your own cam profile designs is a better and more professional choice. I would guess that every cam grinder has copied other cam profiles at some point. It is the easiest way to get started grinding camshafts. After awhile you will want to have your own designs.
Unless you just want to design cam profiles, paying someone else for this service will be more practical. Cam design software is not cheap and neither is your time. After buying the software, you will need to spend time learning how to use it. It will also take years to become proficient with it. Being able to talk with someone that can design cam profiles and then actually having some designed at a decent price can be frustrating. I am probably one of the most affordable and easiest to deal with, of the designers out there.
Once you have a cam profile design, the next step is to make a master plate. There are a couple of options here. You can send the necessary design data to someone with a CNC cam grinder and have them make the master for you. This usually produces the best quality master and is also the most expensive. Having just a few masters made can add up quickly. The other option is to make your masters with your own camshaft grinder. To do this will require that you make a cam profile model first. The model can be made in a vertical milling machine with a horizontal rotary indexing table. Using a CNC milling machine is the best way, but a manual machine works fine also. A used CNC mill is very affordable today and can be useful in making index plates, which you are also going to need. The lift table from the cam profile design data is used to whittle out the model. The cam profile model is then put into the camshaft grinding machine and the master is made in the same way as if you were copying another camshaft. This was the best method available before CNC cam grinders came along. It is still a viable method for those on a small shop budget. There is some more information about this in previous posts, so be sure to read all of them. I have generated many models and master plates and will be glad to give you more detail about this method or anything about camshaft grinding, just ask. Good luck on your new adventure.
Relation Between Lift And Duration
I can always use your help coming up with new topics. Just send me an email with your suggestions.
In my entries about cam profile designs, I intentionally try to make it simple and easy to understand. The information is intended for readers that have little or no experience with cam profile designs. It was very frustrating to me when looking for information, that everything written was mostly about mathematical equations. Most of the information is written by mathematicians and not people that actually design cam profiles used in real engines. Most people are not looking for that type of information, thus one of the reasons for this blog.
Software programs and computers do all the math when designing cam profiles. I have no desire designing cam profiles by hand without a computer. I do understand the complex mathematical equations and calculations that are involved, but I do not want to read or write about that stuff. Again, that is what the computer is for. The design software cannot tell the difference between a good profile and a bad one. That is the type of information I like to read and write about.
Now on to the topic of this entry. Here is a simple example to help you understand. Mark off two points in the street. One point is where you are standing and the other point is some distance away. The distance between the two points will be the lift. The duration will be the time you have to go from one point to the other and back. Lets say the distance is 50-yards and the duration is 1-minute (60-seconds). To go the distance (lift) in the allowed time (duration) will be a slow speed walk (low velocity). If you run (higher velocity), the time (duration) it takes you will be much less than the 60-seconds. Your average speed (velocity) is determined by the distance (lift) and the time (duration) you have to go the distance. You cannot go faster or slower or the time will change. Simple physics determines this. You could run in spurts combined with slower walking periods and still complete this in the 60-seconds time frame. That would create large swings in velocity (high acceleration) and be harder on you than the slow, smooth, easy walk. By the way, you are the valve train.
Let’s change the duration from 60-seconds to 30-seconds. The lift stays the same at 50-yards. What will this do to the velocity? The velocity will naturally have to increase since you now have less time to go the same distance. Your original slow, smooth, easy walk will now be a run. Cut the duration in half again. The duration is now 15-seconds. You must run even faster. You can see the pattern. At some point, the velocity and acceleration will be too much for the runner to maintain. The same physics applies to cam profiles.
Keep the original duration at 60-seconds but increase the lift to 75-yards. That will create the same situation as above. The velocity will naturally have to increase also. You now have to go a longer distance in the same amount of time. You can see the same pattern here. This also applies to cam profiles.
Normally in cam profile design, the lift is chosen first based on the physical layout of the valve train or because of some racing class rule. The duration is chosen next based on the engine size and the rpm wanted for peak power. The lift and duration along with the ramp designs will determine what the designer and the software can do with the lift, velocity, acceleration, and jerk curves.
It is not really a big deal that the duration and lift is off by a small amount from the original design. A larger or smaller profile can be chosen easy enough. It is just not acceptable today like it was years ago. Even though the duration and lift numbers were slightly off, the velocity, acceleration, jerk, pressure angle, and radius of curvature values were still close to the original design. Today, the duration and lift numbers may match what is published, but other numbers that are more important are not even considered. Most customers do not look at this part of the cam profile. Since the customer does not care, the camshaft grinder does not care either. That is why cam profiles are still copied and used in the wrong applications.
As long as the camshaft numbers match the specification card, everything is good… right? No, everything is not good. When cam profiles are chosen based on duration and lift alone, much of the cam profile potential is ignored. I have talked about this in previous post, so I will try not to over repeat myself. When base circle diameters and roller wheel diameters are changed from the original design, other important parameters also change, not just the duration. Opening and closing ramps may not be correct for the application. Problems in the valve train can be created including premature wear of the tappets and the valve springs. This can come from excessive values of acceleration, velocity, jerk, pressure angles, and small radius of curvature in the profile flanks or the nose. Unless these parameters are also analyzed, you are just hoping for the best and so is your camshaft grinder. There is much more to a cam profile than just duration and lift.
Camshafts And Consumers... part 1
Camshaft consumers have been getting more sophisticated over the years. Engine builders and even some individuals are checking their camshafts with a computerized cam profiler before installing them. Those not using computers are checking their camshafts with a dial indicator and degree wheel. This has caused the camshaft grinder to profile each camshaft on his own cam profiler before sending it to his customer. The camshaft grinder uses the actual data retrieved to create the camshaft specification card. This prevents having to explain later why the camshaft specifications do not agree with the card.
Years ago when computer designed cam profiles were becoming common, a model lobe was created from the design data in a milling machine and a cam profile master plate was then created from the model in the camshaft grinding machine. This was before CNC machines were used to make the master plate from the design data. The master plate is used in manually operated camshaft grinding machines to make the camshaft. The most popular machines are the Van Norman and Berco camshaft grinders. There are many of these machines used today to make camshafts. The machine uses a follow wheel to trace the master plate shape onto the camshaft. There are many videos on the internet showing the operation of these machines. Check them out if you are not familiar with how a camshaft grinding machine works.
Between the cam profile design, the making of the model lobe, the making of the master plate, and the making of the camshaft, many errors are accumulated. I am not sure but I may have just let out a big secret. I always say, there are three different cam profiles for each design. The original design (1), the actual lobe on the camshaft (2), and the profile that is created in a running engine (3). Obviously, you want all three to be the same, but in reality, they are not. Today’s technology is allowing them to become closer. Making master plates directly from the profile design data using CNC machines has removed many of the errors experienced years ago. A well maintained Berco camshaft grinder and CNC produced masters, along with a skilled operator, will produce a wonderful camshaft.
Back to the years ago. There was usually a big difference between the original cam profile design and the finished camshaft lobe. A decrease of around 2-3 degrees in duration and 0.003 in lift were common discrepancies. This was from the major camshaft grinders of the time. If the camshaft grinder created the specification card from the original design, and most did, the actual camshaft specifications did not mach. Most people did not analyze their camshaft at the time and the small differences in specifications were usually accepted. It was just considered the normal tolerance. Today, the consumer expects to receive a camshaft with all the lobes matching the specifications exactly. Unless the camshafts are being ground on CNC machines, it is very hard to deliver that kind of quality. Profiling the camshaft and using that data for the specifications, is the only way to make them match and please the customer.