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Cam profile design
10

Cam profile design

Cam profile design

(OP)
Hello,

Just discovered this forum. I have been searching for a forum on camshaft design. That is, actual design like ramps, profiles, materials, machining, and so on, as opposed to "what cam should I use?" I found a gear forum but no cam forum. Anyone know of one, or is this forum the appropriate place?

Thanks,
John Woodward

RE: Cam profile design

2
(OP)
I have many old SAE papers and the polydyne papers from Machine Design. I worked with Harvey Crane for a while on a new aircraft cam, and also know the guys at Comp Cams as they are across the street from where I used to work. I eventually wrote my own program but I still do not know as much as I want to.

Thanks,
John Woodward

RE: Cam profile design

Is there a basic formula for the valve spring pressures need on flat tappet hyd. cams.  I'am interest in using as little pressure as possible for max 4500 rpm truck engine. Some cam manufacture recomend 400lbs/in springs and others recomend 250/spring. I liketp find a formula that takes into account the following,,,, valve, retainer and 1/2 the spring wieght, rocker ratio, and lift per deg of rotation. Am I out in left field here?      

RE: Cam profile design

(OP)
To RacerRick,

There are equations scattered about in the literature but nothing basic. I don't know of any that you can use as is. They usually take a lot of manipulation to put them in a workable form and then they are too time consuming to use unless you write a program.

You have to know the cam profile to get the valve lift and acceleration at every degree. You already have the weight of all your components. For the spring you need to know the compressed load at one point and the spring rate. Basically the formula starts with

Force = Mass x Acceleration

You calculate the inertia force on the valve train created by the cam acceleraton, using the above equation. Plot it for 360 degrees. Next, calculate the spring force applied to the valve at every degree and plot it on top of the inertia force.

There should be more spring force than inertia force at every degree. It is not enough to do the calculation at max lift, as there could be points in the early stages of lift where the curves get close together.

Exhaust pressure also needs to be considered. The exhaust valve has to be opened against cylinder pressure, which can cause high forces, and in a turbo engine the exhaust port pressure cam overcome the spring seating pressure.

Of course, none of this has answered your question. To meet your immediate needs it may be best for you to go by the cam manufacturers recommendation, especially if they offer a kit.

John Woodward

RE: Cam profile design

Racer,

There is a formula in Joseph Harralson's "Design of Racing and High Perforance Engines" that might be of some help to you. If you're not familiar with the book (ISBN 1-56091-601-X) it is basically a collection of SAE papers. Here's the excerpt which deals with abnormal valve motion:

"VALVE MOTION- Abnormal inlet and exhaust valve motion is a major obstacle in the development of high-speed engines. The main factors influencing valve motion are:

1. The degree of ridgidity in the valve train.
2. The equivalent inertia weight of the moving parts in the valve train.

For the tappet-type and rockerarm-type of overhead cam valve mechanisms, we determined the engines speeds at the initiation of abnormal valve motion (such as jumping or bouncing) and plotted these data as a function of the equivalent inertia weight of the valve train.

It can be seen that the abnormal motion begins at a higher engine speed for the tappet-type, which can be attributed to the higher ridgity of this system. The equation generally used in valve mechanism design is expressed as:

Ne = 2C SQRT[(Fs·K)/(W·(-y))]

where:

Ne = engine revolution speed
Fs = valve spring force at maximum lift, kg
K = G(30/pi)^2
W = equivalent inertia weight of valve train, kg
y = maximum negative acceleration, mm/rad^2
g = acceleration of gravity 9.8x10^3, mm/sec^2
C= correction factor

In order to predict the engine speeds at which valve jumping and valve bouncing will begin, we empirically determined the value C as follows:

C = Cj =0.85 (for valve jumping)
C = Cb =1.0 (for valve bouncing)"

Sorry for the length but wanted to get everything into context there.
I post this in hopes that someone can maybe explain it. I'm a sophomore in college working towards an ME degree so I'm kinda stuck waiting til I have a better understanding of kinematics and dynamics before I can extrapolate anything from this on my own. I'm sure someone can shed some light on this though.

Best of luck.



RE: Cam profile design

(OP)
Mr Prog.,

Can you supply the SAE number of the paper? I don't have the book but might have the paper.

I usually don't bother with empirical formulae if one can be derived on a scientific basis. You should soon be able to do this, although you may know enough already. It is just a matter of writing F=ma for the valve train inertia, but writing it as a function of cam degrees. Acceleration is from the cam profile. You can get it by differentiating the polynomial equations if known or if you have a lift table find the difference between 2 lift points for velocity and the difference between 2 velocity points for acceleration. The mass comes from the weight of the moving parts in the valve train, taking into consideration the rocker arm ratio. I don't remember the definitions; I can look them up if you want.

Now you have valve train inertia force vs. cam angle. Next you calculate the spring force at each cam angle. If you know the spring force with the valve closed, you then add to it lift x spring rate at each cam degree.

If someone would tell me how, I would like to post an illustration here that would take the place of all these words.

John Woodward

RE: Cam profile design

Thanks for the help John, I need to digest this before I can ask any pertinent questions.

The paper I referred to is, "Research and Development of High-Speed, High-Performance, Small Displacement Honda Engines" SAE #700122

Valve motion is dealt with in the mechanical efficiency section of the paper but only in brief.

Another paper that you might be interested in is, "Modeling and Measurement Techniques for Valve Spring Dynamics in High Revving Internal Combustion Engines" -Ford Motor Company SAE #930615

Of course most of the information in that paper is well above my head at this time but it is very informative.

Thanks for your time,
Allen

RE: Cam profile design

John,

Specifically, what do you want to know?

RE: Cam profile design

John You mention writing a program. Do you know of any good programs that will do the math for me?  I looked around the web and there are a few. Now I need to know which one to buck up for? Thank

RE: Cam profile design

(OP)
Rick,

Let me know where you found the programs. I would like to look at them. My searches never turned up anything.

The program I have is written in Visual Basic. I obtained the equations from some old SAE papers but they required considerable modification to make them usable, and also to be able to solve them. I added lots of things like ramp calculations, plots, lift tables, etc. Other programs in the group calculate valve spring forces and valve train inertia throughout the range, and cam and lifter stress. The main program is for the design of the profile. A smaller program will generate plots from a lift table.

At one type I worked with Harvey Crane and used his program. My program gives the same results, but to me it is easier to use. It is similar in principle to what they use at Comp Cams but not as sophisticated.

I have half a mind just to give it away to anyone that wants it. Trouble is, I am not sure it will run on another computer without VB being installed.

John Woodward

RE: Cam profile design

Don Hubbard's "Camshaft Reference Manual" is a very detailed reference on the low level details of camshaft design. Pricey but worth it, and it comes bundled with some very good software.

Professor Gordon Blair of Queen's University of Belfast wrote a very sophisticated cylinder head design package that covers very detailed cam and spring design details.

Details at http://www.profblairandassociates.com/GPB_Products_Main.html


Some good cam design references can be found here:
http://www.audietech.com/CAMBiblio.htm

I hope this helps.

Rich Rohrich

RE: Cam profile design

Dennis,
I would be interested in your cam design sources as well.
If you could e-mail infos, design software and so on to me would be great.
Thanks
Alex

RE: Cam profile design

I should have posted more the first time...

I work for a major tier 1 supplier of valves and valve train parts.  We do not design camshafts, but we are very knowledgable on their design, materials, dynamics, etc.  

What specific questions do you have?

Chris Hill

RE: Cam profile design

(OP)
Chris,

Lots of questions as I think of them, but let me try this one:

I know how a flat tappet cam is ground, for example, using a Norton grinder and a large wheel. The same lift table can be used for a flat or roller cam, but the shape of the lobe is very different. The large radius of the large grinding wheel approximates a flat lifter. However, it is not very clear to me how a roller tappet cam is ground. Since the profile depends on the roller diameter, what size grinding wheel would be required, and how is it determined?
Equations would be great so that I could add them to my program.

Many thanks to anyone who can provide this information or direct me to it.

John Woodward

RE: Cam profile design

jlwoodward,

I've never actually seen a cam being ground, but I do know that different manufacturers will have different concavity limits (minimum allowable amplitude of negative radii), which I assume are determined by the size of the grinding wheel that they use.  A program such as Camspring (Ricardo Software) can calculate cam cutting ordinates for just about any combination of valvetrain geometry and follower diameter.  Sorry that I can't get you any closer to writing the equations yourself, but if you happen to get a copy of the user manual for Camspring, the equations might be in there (not sure).  If you're doing this work for your boss, perhaps you should push him to get a trial copy of some off-the-shelf cam design software.  It might be worth the money.

Regards,
Isaac

RE: Cam profile design

John,

Sorry for taking so long to get back to you...

I'm not real strong in this aspect of cam design, but here goes.

Basically, you have to determine what the radius of curvature of the cam needs to be for a particular lift profile vs. roller diameter.  I'm not sure how to explain it though.  But I do think some calculus books address this issue.

If you have some dynamics questions I'm better with those.

RE: Cam profile design

John & Chris,

The cam profile depends directly on the geometry of the roller follower. You will know/notice that the cam profile for a roller follower may have a concave portion and it is the radius of curvature of this portion that determines the diameter of grinding wheel that can be applied. The max cutter radius is limited to the min absolute value of the rad of curvature in this portion. (otherwise it would physically not fit into the concave!)  

RE: Cam profile design

Ther are very few cams with IR flanks that can't be ground with a std. wheel and machine.  We  lay a straight edge across the cam flank to see if its concaved. If it is we use a 14" wheel. You can buy attachment to run a 7"wheel but I have yet to come across a cam that needed it.  I checked with a cam doctor. I guess some wild ultradyne or IR crower might need a smaller wheel.
 John when grinding any steel cam, we slow the cam rotation way down to prevent chatter. Its no different than grinding a cast cam except for the time it takes.

RE: Cam profile design

8
Get away from Hydraulic cams. If you want to make power, it is time for a clearance ramp cam. Do Not fall victim to the statement: You can't run solid lifters on the street because they have to be adjusted constantly. This is a wide spread mis-guided criticisim of clearance ramp cams. They are constantly being adjusted because the locking method used to lock the rocker arm down is either not utilized or is totally installed wrong by the ameteur. 99% of the cams I personally sell for street/marine engines and 100% for race engines (accept where rules ban me from doing so) are solid flat tappet or solid roller cams. If you take a .025 lash cam and set the lash at .019, the valve train is almost void of any solid lifter noise. Makes a Great Sleeper! The reason you need to run from hydraulics is that they are slow and lazy opening cams compared to clearance ramp cams. For example: a solid with 264degrees advertised duration @.020 is 235 @.050 VS a hyd with 280 advertised @.0045 is about 230 @.050. My point is the 264 opens later thus smoking the much earlier and slower opening hyd at slow engine speeds, and also will beat it up stairs too. You see it is caught the nearly 20 degree bigger hyd by .050, so what do you imagine it did to it up @.200? It is actually bigger!!! It is smaller in the motor before TDC, but bigger after. (It lies to the motor) And since I am ULTRADYNE, I'd like to say that we are the only ones that will show our cams at.200. It's kind of funny when I speak with other cam manufacturers(wanna be cam designers that are largly cam copiers)when they tout their seemingly cool duration @.050 numbers, They are dumbfounded when I ask them what the .200 is. We are the only true mathametically non compromised cam design. Dont be fooled by a so called computer designed cam. It is only as good as the programmer.         

RE: Cam profile design

Well ShaunT,

I will not disagree with your reply, a hydraulic cannot keep up with a flat tappet or solid roller. This post originated about cam design and I am shure you could provide input to that as well. I will take up the "other cam grinders not knowing the duration" at other lift numbers. Two come to mind Iski, lists the duration at all lift points up to max lift right in the catalog, second is WebCam, they may not publish the numbers but call and talk with them or in my case stop in and they have that and more.

My question to you is if I call your shop on Monday one week, Tuesday the next week and Thursday the following and ask for a cam recomendation for the same motor: How many different cams will be recomended and why?? What I have not found in cam companies is any remote shred of consistancy in cam recomendations.

This makes me question anyone that claims to know "all the answers". Cam design the original thread still seems to be a black art, some no doubt do it better than others. Some continue on old reputations and others on truly new designs but none seem to have resolved all the questions.

Regards

D Friedeck

RE: Cam profile design

(OP)
Hello Shaun,

I have a request to ask of you. If we could go back to my original questions at the top of the thread, I wonder if you could share some of your cam design experience with us. Your comments about cam performance are very interesting, but I would like to learn more about the actual design and manufacture. For example, do you design your own profiles, and what tools do you use, such as computer programs or good old intuition. Do you grind your own cams? Please understand, I would in no way ask you to give away any trade secrets that you have worked so hard to learn.

Thanks,
John Woodward

RE: Cam profile design

We design and manufacture all of our profiles. We use a program that we created that uses for the most-part, 6,7, or 8 decimal place polynomial equations. We can do this by hand with a calculator, but the computer allows us to do it millions of times faster. In the old days, using a desk-top calculator would many times give a design that might not show up flawed untill it was ground. A couple weeks lost.
Our cams are 6 or 7 different sections, each section can contribute up to 10 million different cams at any given lift in the section. Some would be too big,others small, some could not physically be made, and others might only be different in millionth of an inch increments. Engines react to different curve families and do not notice differences in millionth's of an inch. We have a very slow initial opening to minimize reversion, then we open it fast. We are able to catch cams at .050 lift that are 6-10 degrees bigger at the seat. We also slow the closing down for two reasons. 1:we build so much more port velocity than others because even though we may open the valve later, we start flow sooner because a reversion in the port costs valuable time. A port that starts flow late, will never catch up. Due to our higher percentage of clean air flow, we get to #2: The more velocity I build, the longer cylinder filling will continue to RAM the cylinder after BDC. So, why hurry and shut the valve? Take advantage of inertia! Close it slowly unlike conventional Symmetrical designs. It gives you extra time and it also shuts gentle enough to stay shut taking advantage of ALL of the charge, and (here is the good part) Your intake port does not have a reversion due to a valve bounce during the compression stroke. So when the intake valve opens again, It will fill instead of having several crank degrees try to reverse the reversion. The proof that we pick up the flow is the increased fuel required at high RPM since an increase in air flow demands an increase in fuel also. This is why many Blowers are blowing the burst panels. Years ago, We were the only ones that did not cause this to happen in a test of a Nitro Hemi conducted by a really big name.(Almost a house-hold name to racers) We also picked the motor up nearly 500 HP with ten LBS less boost than any other cam they tried.           

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

I love this stuff.

Shaun T ULTRADYNE Arl,TX

RE: Cam profile design

There are also manufacturing processes involved. One simole one is the immersion of flat tappet cams into a hot tank of phosphorus. This is the Black stuff on the cam lobes. I have had many cams come back to me for a freshen up. Once i check every lobe for wear and they all check out good as new, I re-phosphate the cam and send it on its way. There are on occasion people who will say they had a cam and it sucked because it broke in two pieces in the first 5 minutes. This is not the fault of a cam grinder accept in one area. He dropped or hit the cam core which fractured it. Usually though, the cam is damaged in transit. There are only Two cam core manufacturers for American V8's in America. Incidentally Crane owns one of them. They are cheaper than others largely because of that and the fact that they "Gang Grind" cams. For ALL of you Ford 5.0 fans out there, Crane also produces the Private labeled Ford Motorsports cams.   

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

>>>I have half a mind just to give it away to anyone that >>>wants it. Trouble is, I am not sure it will run on >>>another computer without VB being installed.

If you have the full version of VB, you can create an executable out of your program for us all to use.  I have the full version and could try to do this for you if you don't.

RE: Cam profile design

Shaun,

I basically understand your theory of cam profiles. One thing I have a question about however, is why we could not open the valve quickly at first? Could not the duration be decreased with a faster initial opening? Or are there other requirements (like peak lift?) that need to be considered?

Thank you!

RE: Cam profile design

You can't open it with a high jerk if you want to engineer a cam to live long enough to win and win again. It also will induce valve float due to the inertia load. You will also spit roller bearings out in every direction. When you open it fast before TDC, you induce a ton of unnecessary reversion and hence delay cylinder filling. In terms of power, reversion is the enemy. A port that starts flow late will never catch up. The port with the higher velocity will continue to ram the cylinder after BDC and that is the origional reason for the long and slow closing. It buys time to take advantage of the inertia ram  from the port. It also shutsa so softly that it stays shut keeping ALL of the mixture in the cylinder and therefor ALL of that power capability there. The best part is not putting a reversion in the intake port from the flow         valve opening on the compression stroke, and hence starting flow sooner on the next intake cycle.
 

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

So let me see if I understand.

The slow initial opening (prior to TDC) is to take up clearance and get the valve moving in a smooth manner. Once past TDC, you want to open the valve as quickly as possible (short of mechanical problems).

Did I interpret that correctly?

RE: Cam profile design

You have most of it down.  The other reason for slow movement is to minimize port reversion. Virtually all cams open the initial opening much faster than US. We all understand that having no reversion would mean opening at or after TDC. Then we would have to explode off the seat to move any air. All of us here  also understand what that would do to our valve train.   

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

Not sure what engine types you are refering to but I would suggest contacting KAMS inc in Oklahoma email: jeff@kamsinc.com. They design and build special cams for large diesel engines

RE: Cam profile design

Yeah. Some one here in Dallas that I know uses them.After looking at one, I told him I can make one for him that will beat it badly in economy, power, and valve train reliability. But, you know, not a priority with the slow economy now.   

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

There are different acceleration families that are intended by design to do different things. The really fast opening cams are very effective in limited breathing stock cylinder headded motors such as Super Stock class drag racing. They also would be well in lift rule restricted Stock class drag racing that are usually limited to flat tappet cams. The really fast lobes I mention here are very good at making torque and horsepower, but are not stable at 9000+RPM's like a slower opening big lobe lift piece. Such pieces are found in Road Race engines, Endurance, Super Gas, Pro Gas, Comp Eliminator, and of course Pro Stock. Many of the slower cams with big lobe lifts are teamed with high ratio rocker arms to achieve "big" net lifts. when a motor has a big port and one that flows very well, it can hurt power with a very fast ramp because it gents into a situation of having the ability to keep up in terms of port velocity.

We consistently shock the Pro Stock engine builders with the gains in peak and total torque plus the dramatically increased valve spring life and stabilized pressures they discover when using our cams. Most of them find they need to run some rediculous (in my opinion) spring pressures to stop float and bounce associated with many cams. when they are used to throwing away at least half the valve springs every 2-3 runs, you can imagine their satisfaction at keeping them for at least an entire national event race. At upwards of $500.00+ per set, who wouldn't be satisfied?       

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

Shaun,

I hate coming across like a testimonial, but I guess I have to.  For those that don't know, I run Ultradyne rollers.  Although not big block Pro Stock engines, they are very potent N/A and Nitrous small block engines capable of comfortable 7 second 1/4 mile ETs.

A recent combination went an entire 20 event season on a single set of valve springs.  True, valve lift was only .778" and rpm was only 8500, but I still think that is pretty remarkable.  Another surprise was, the springs were only 255# on the seat and 715# open.

The valve job looked new at the end of the season as did the entire valve train.

There has to be something you guys do at the "transistion points".  

RE: Cam profile design

Oh yes indeed!

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

How many of you have seen the brass colored evidence in the oil form pulverized needle bearings? I have seen this even when the bearings are still in tolerance. If you practice inspecting lifters and rockers in a race engine on a regular basis, you will pay yourself big dollars through avoidable disasters. You can also significantly increase the needle bearing life by using a full synthetic oil such as MOBIL1 or ROYAL PURPLE(not too heavy.) One of the areas you can help to minimize roller lifter tracking on the cam lobe is to throw out lifters with excessive bearing clearance. Some will say "they are about wore-out but they will be okay for a few more races."  Then I get a call or Email from someone asking for help in a hurry because the roller lifter came apart and hurt a lobe. I will also tell them to pull the oil pan and inspect rod and main bearings because I am very confident that the trash from the lifter and cam ended up in your oil system and consequently some bearings.  I have to re-do their bottom end about half the time.  
Guys, It doesn't pay and it usually costs you Big Time, so don't gamble, especially whti the valve train.        

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

First sentence should say "from pulverized needle bearings",
not form pulverized needle bearings. TYPO, sorry!

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

Here is an example of two cams with the same seat or advertised durations, but intended for different purposes.

310@.020 vs 310@.020

282@.050 vs 275@.050

203@.200 vs 192@.200
One is quite bigger everywhere after.020 Obviously, it will make more power EVERYWHERE, but it will need more spring, and will not be very dynamically stable above 7500-8500 RPM's (depending on rocker ratio)

One is an NHRA Super Stock national event winner, and the other is a 24 Hour Lemans and 24 hour Daytona winner.
Big difference in environments here.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

(OP)
Do excessive jerk pulses tear up the needles, or is it just high spring loading? Are needles in rocker arms also affected?

Thanks,
John Woodward

RE: Cam profile design

Yes and Yes. Excessive lash settings, higher rocker ratios, and bad rocker arm geometry hurt things too. If you have to run the lash loose to go faster, you are likely lacking in the fuel department, and/or the cam is too big for your needs/RPM range. I have stated before that running solid roller cams with 300+LBS seat pressures in anything other than forced induction(and serious boost at that) is bad. I stand firm in the belief that a cam that has to have that much seat pressure to control the valves in a typical American V8 needs to go in the trash can.    

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

It is a rush to go cruising with customers in their cars. When a customer has an aspirated motor at only 8:1 compression, and no power adders, it makes my day when the car runs so good that everyone thinks it is a really big motor with a solid roller cam and tons of compression. Actually, the most recent case from this last Saturday Night is a very successful combination that utilizes a fast ramp flat tappet cam that has a short seat duration, and a middle of the road LSA of 110 with a 104 intake C/L.
Why? Because it only has 8.17:1 compression. The motor runs hard to 6500. I see low compression (especially carbeurated) motors with some huge seat duration cams with stupidly wide LSA's way too often. They are usually in heavy cars with automatic trannys too. People always ask me what is their best choice for LSA. I like narrow LSA's even when compression is not an issue.
The narrower LSA's aid low comp motors. I feel that most of the choices made by consumers are due to ignorance. Many cams are so lazy in reguards to high lift area, that they only RPM because of their wide LSA. I see this in Pro Stockers daily. I also change their opinions and make them smile daily. But, Pro Stockers are the Extreme and they don't get my recommendation of 106 or even 110LSA cams. I usually preach 114 to them when everyone else is 118.

Economy and emissions aside, and since they flatten and broaden torque curves, low compression motors only need wide LSA's when they have really small cams that are also having to RPM. In Drag cars, the 106 LSA's are hardly ever slower than 112 LSA's especially in heavy cars with automatic tranny's. In dirt track cars, sometimes a 108 will be faster than a 106 simply because the track is slick, or the driver is having trouble controlling it and putting it to the track and he is getting out ran on the top end. Incidently, I recomend 108's to dirt trackers regularly. Many of them are my own loyal customers with 106LSA's who call me reporting a problem such as hard to hook up and also running out of steam a little early. A 108LSA fixes them and usually they win the race. My advice to the big cam wide LSA heavy car with small motor and low compression scenario's is: Either narrow the LSA 4+degrees or remove about 15+degrees of seat duration from the motor, and open the valve faster if you don't want a  motor to be a slow reving lazy dog (especially one with low compression) with your wide LSA cam.
Bersides, It will be alot funner to drive and have more hit at idle, which is something most ask for.       

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

I will comment on something I have advised about in the past. When looking at Hydraulic Cam specs, make sure you look at advertised duration. If they are showing it at .006, it is a lie. In other words, the cam will open the valve at approx .0045. This will add SEVERAL degrees of duration to the opening of the valve depending on oil thickness/temp, but it will not add any duration  at .050 or any where else. Here is an example of a cam that I LOVE to pick on: Marketed as a 292 Magnum H10 (what a Dog)
It is advertised at .006 with a .050 of 244. However, it is over 300 duration at .0045, hence it is quite a bit bigger in the motor than it is on paper. Even though this is a STUPID mass produced junck camshaft, I will say that if all that was changed was the offering of this cam ground on a 106 LSA, it would be a major improvement in overall performance. I love to sell guys a cam to replace this one. It is awsome to watch their car run a full second  or sometimes quicker in the 1/4 mile with the new cam that is many times 20+ degress less advertised duration and still runs over 7000RPM with power. For anyone who has this cam, have you noticed that at WOT the motor seems on the brink of exploding into it's power band, but it never does. It feels like it wants to really bad. It gives me that sensation all the way through the RPM's. It is a let down. Incidentaly, I have never seen anyone buy a cam like that unless they are still very wet behind the ears and wouldn't know what real power feels like. They think they do, but are clueless.    

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

(OP)
Hi Shaun,

Do you mean that both cams are 244 @ .050, while one cam is 300 @ .0045 and the other 280 @ .0045? It sounds like a difference in ramps.

John Woodward

RE: Cam profile design

Sorry for the delay. The difference is in the ramps. One is advertised at .020 while the other is advertised at .006. Incidently, one is a Hydraulic, and the other is a Solid. They are the same at .050, but the solid is much smaller at the lash point and much bigger up at .200 and over the nose. You can put these two cams side by side and see a visual difference. One is a pointed nose "Hatchet" cam, and the other one has a nice fat rounded nose.  

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

Here is a tip for those of you who also like to race on dirt. I have several cam profiles that are a little better in rate than the one cam that made us famous, especially in the dirt track arena. It is the 288 296F6 and the 288 296R6. One is a solid flat tappet, and one is a solid roller. Both are on a 106LSA. This cam is very good on tacky dirt tracks as it is very strong off the corner. It has a ton of mid-range. The roller runs hard to 7800 in 350's with 6 inch rods. Especially with Alchohol. I have many clients who swear by this cam, however after I quiz them they tell me that once the track dries before the last race, the car is very hard to put the power to the ground.
Here is my tip: If you need some more RPM and need to soften the shock on the tire when getting back on the throttle out of a turn, try a 108LSA. You will take some of the mid-range "spike" out of the motor, while giving it a little more down low and extending it on top. Once you try this, you will see the motor pull upwards to around 8300RPM before it fades away. If the 106LSA cam is faster around the track after a spark plug wire is disconnected, you need a 108 because the 106 is blowing the tires in the corners.    

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

I spoke with a dirt racer the other day who has a short stroke long rod combination. He told me that I can't take a bunch of seat timing out of the motor because he runs a very limited right rear tire and if I put a bunch more torque in the motor, he won't be able to control it. I explained to him that the shorter seat timing cam with the faster ramp speed than his current favorite, can be more controllable because it won't act like a LIGHT SWITCH.
Here is an update: He is now running lap times that are right in the middle of the 410CID territory. Funny thing is that everyone protested him by saying he was running a 410 inch motor in the 360 inch class. Everyone was STUNNED to find that upon a tear down inspection, it was less than 335 inches. HA HA!  

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

I have been receiving a fair number of comments about people being affraid to run Flat Tappet cams because of lobe failure experiences associated with break in Etc.
While my reply here does not relate to cam profile design, it should shed some light on things and calm some fears.
There are few things that can go wrong with a cams ability to deliver a long life. One big problem that is not too common, but will surely kill a lobe is a block with an out of spec lifter bore angle. Ever continously change cams and lifters only to keep killing the same lobe? It's time to have your blocks lifter bores trued. While you are at it, have them bored to a bigger size too.

Here is a simple break in procedure for flat tappet cams that I personally have never had fail me even on 600+Lift Big Block Chevies with 140lb seat pressures. Keep in mind that all of this is in vain if you grind on the starter for an hour before the engine fires. It's also a waste if you are not practicing Hygiene.Assuming things are ready for assembly, step one is to clean all components with Lacquer Thinner and then visually inspect things. Next, Take some A.R.P moly paste( you know the stuff they give you with their Rod Bolts, it's the best.) put it on the bottom of the lifters and all over the cam lobes. Then, pour some 5W20 non synthetic oil in a clean bowl and dip the lifter in upside down to coat the body. Put some oil in the lifter bores too. This assures the best possible chance for the lifter to spin.(this is why you don't use synthetic oil on break in of a new cam). Make sure that end play of the cam is around .010. Put a thrust button on it if you have to.(You will be amazed at how this really cuts chain stretch,especially in Chevy's) Once it's all installed and valves set(I like to set solid lifters .005 tighter then typical .025 spec, this also means an additional .005 tighter for cold lash on Alum Heads), put some of that 5W20 stuff in the oil pan and filter. Now prime the pump untill the oil comes out of the rocker arms. Once you are ready to fire, assuming the fuel system is primed too, it should light off instantly, and run at 1800+RPM's. After a few minutes, drain the oil and put in a fresh filter and fresh oil. Now, go play.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

Has anyone ever seen a square nose cam? Ever rotated a motor and watched the square nose cam toss the lifter off the back side of the cam's nose while watching the valve action? Slam! Bounce,bounce. Too bad we don't have the sound effects from the cartoon's of the 60's.  These are cams with extreemly high negative nose deccelerations. The NHRA stocker classes are flooded with cams like this.   

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

RE: Cam profile design

????

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Cam profile design

It would seem to me that there is little point in that, since a bouncing valve might have a similar leak-effect to a slower closing one? Is that what you're getting at?

RE: Cam profile design

What I am getting at is that when a valve bounces, the piston is at or very near max velocity on the compression stroke. Bouncing the valve creates an instant hichup in the intake port. A valve usually bounces open a couple of times. Closing a valve a little slower and hence later creates a tighter packed cylinder if you are using it to compliment the inertia you have created from the opening side of the cams ability to minimize reversion via our design. When the reversion is kept down, more real time has been allowed to build velocity in the port and fill the cylinder. The more velocity (inertia) we build in the port, the longer the port will continue to fill the cylinder with a charge after BDC. This is why our origional consept of a slow closing was born. Remember: a port that starts flow late will never catch up.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Cam profile design

(OP)
Square nose cam-

We have a cam that is flat on the top, with a small radius on each corner blending into the flanks. I don't know why it was done like that. The negative acceleration segment has a sudden change over the nose where it drops to zero and then back to negative. There are also extra jerk spikes because of this. I don't know if this was having any effect on the performance, but I just converted it to a smoother polynomial profile. We don't have enough test time  yet to tell if it is better. The problem we are having is pounding out the exhaust valves and seats.

John Woodward

RE: Cam profile design

If I read you right, you have a dwell profile, where peak lift is maintained for a time. The acceleration profile will show a ramp, a flank, a negative region, a zero region, a negative region, another flank, and another ramp.  Sometimes there are constant velocity portions (zero accn) between the flanks and the decel-to-dwell portions of the profile.

 That is sometimes done when the cam designer wants to increase the period without increasing peak lift, and wants to maintain the same flank rates.  If the springs could take the additional lift (or whatever other constraints weren't there) it would probably be preferable from a vibratory standpoint to use a more "normal" looking profile, and it will probably improve your seating velocities, but sometimes that's not an option.  If you keep the same period and peak lift while removing the dwell portion of the profile, you'll be reducing the area under the lift curve, which may have a detrimental effect on breathing.  

I'm not sure what your closing ramp looks like (constant velocity? constant accn?), but sometimes you can bring down the seating velocity a bit by changing from a constant velocity closing ramp to a constant acceleration closing ramp, with little change to the valve timings.  Making the profile a bit asymetric, such that the opening flank has a lower peak acceleration than the closing flank, can also help sometimes.

RE: Cam profile design

(OP)
Mr. Hiding-

Thanks for the enlightenment. Those old-timers new a lot of things that are not in the books today. The springs do not have much room left before coil bind at max lift, so maybe they had to limit lift. I probably did reduce the lift area but this is a low bmep, 3000 rpm engine so it may not be noticeable.

The cam uses solid lifters with constant velocity opening and closing ramps. The thing that did not seem right to me is that the exhaust clearance is .014 and yet the ramp height is only .008 inches. The exhaust valve may have been hitting the seat at a high velocity. I kept the same end points but changed the ramp to .014 (same ramp velocity of .0005 in/deg) which of course made it much longer.

This is my first attempt at designing a cam, so whether or not I know what I am doing remains to be seen. I wrote a nice program though!

John Woodward

RE: Cam profile design

the only reason why I can imagine using more cold clearance than the ramp heights would be if the clearance shrank as the engine heated up (this does happen on some engines).  

RE: Cam profile design

A tighter clearance can reduce bounce. In the case of a square nose cam, I don't think there is much hope for cutting bounce. I've seen some pretty nice low/mid range torque gains by puting a design in a motor without the square nose. We made one a couple years ago that was over ten degrees less seat timing and over ten degrees bigger at 200 than the current favorite. It took so much reversion out of the port compared to the crowd favorite, that the torque was much better everywhere. We are still trying to make it work, since the reversion picked up the airflow past the point of the fuel system's ability to keep up with the motor. Incase you are wondering, these are stockers and rules RULE. Therefore we can't take care of the obvious and still be legal. We try it on the dyno with unregulated motors and the gains over the other cam are very nice. Enough that some racers would kill for. Too bad it won't work with the rules regulated fuel systems/fuel bowls.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Cam profile design

(OP)
It is an air cooled engine with aluminum heads. Valve lash is .008 intake and .014 exhaust. Carved in stone- no one will change it. The intake ramp is .010 high and exhaust ramp is .008 high. Both have the same constant velocity. Of course the exhaust is going to get hit with a much higher velocity by the time the clearance is taken up, and I would think that it would likewise hit the seat at a higher velocity.

I might be interested in trying the accelerated ramp. However, I thought they were only used for hydraulic lifters?

The opinions around here are that it is a temperature problem. However, we are only running part load. Also, valve faces are Stellite, seats are a compatible high temp material, and guides are hardened.

Shimming the springs helped a little but there is not enough room to increase load much before they go solid.

John Woodward

RE: Cam profile design

If the loos tappets are carved in stone, would it be to dirty a trick to grind 0.005 off their feeler gauge, and only tell them after the problem is seen to be solved.

Just hope they don't use the gauge on something else in the meantime.

I ran air cooled VW's many years ago. We set them at 0.004 as they opened up considerably as the engine warmed. This was air cooled, alloy head. The aluminium expands a lot more than the pushrod, but the exhaust valve only expands a little more than the head, and the inlet, not as much as the head.

Regards
pat

RE: Cam profile design

I might be interested in trying the accelerated ramp. However, I thought they were only used for hydraulic lifters?  

Hmmm... I've never heard any such rule.  I thought they were used anywhere that dynamic analysis / testing showed that they reduced seating velocities w/o compromising duration.

RE: Cam profile design

I have seem rectangular cam lobes on old engines circa 1910. I am Manager of a camshaft manufacturing company. We do little design work but plenty of small batch and prototype manufacturing work for engine developers and the OEM. If you need any manufacturing help just as I do this sort of thing every day. Cheers guys

RE: Cam profile design

I wish to stress  something that I have said before, but a bit off the subject from the last few postings to this thread/subject. As Intake Port volume increases in addition to utilizing longer connecting rods, but not running a longer stroke crank( I.E. higher rod to stroke ratio) one needs to be aware that some(Super Stock style) cams with an extreemly high/fast initial acceleration rate before TDC will drastically hurt power and torque because the piston won't create the velocity in the Intake port. When a longer rod is used in place of a shorter one that was origionally used when the origional engine/hed/cam combination was designed,I usually back off on seat duration and tighten the LSA a couple of degrees and suggest a tight lash cam because it has a bit slower initial(before TDC) opening.
ANother trick for any combo (I will use a small block Chevy in this scenario) is for the guy who wishes to run 1.6 or bigger Rocker Arms. May I suggest keeping the 1.5 on the Exhaust. The bigger ratio on the exhaust really sacrifices the low speed torque for very small gains up stairs. The 1.6 on the intake offers the most bang on the big end but spares the low speed to the guy who needs it. When I became a W.D. for Air Flow Research Heads, I shared this with many dirt racers along with info that the Dyno proved. It has really helped make some wannabe's become very consistent winners.  Happy Tuning.   

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Cam profile design

Cam profile design. What about rocker arm geometry and fulcrum points? You can and should always check rocker/push rod geometry anytime a cam is changed or the heads/block is worked. It will take some drag off the motor, and it will save the guides and valve job. As for fulcrum points, it is gratifying to take a motor with all of the springs and components in running condition, and turn the motor with a torque wrench. I have seen 50-70lbs required to turn motors even with the plugs removed. I have also seen the same motors require 20lbs or less when a shaft mounted rocker arm assembly is installed that changes the fulcrum point as compared to the standard stud style seen in your typical small block Chev or Ford. I love to see the leverage work the magic. This is some fairly nice increase in power too. Some of the shaft style rocker systems are becoming pretty affordable too.
I love this stuff!!

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

RE: Cam profile design

About all this flat tappet cam break in stuff.
And minimum rpm to do such.
I know some of the thoughts on why.

But there are many engines that have flat tappets that never go over 1300 rpms.  So kinda blows holes in that one.

RE: Cam profile design

hmmm... maybe it's a "minimum average rubbing velocity" question, then?  A 1300rpm engine most likely has a larger-diameter cam than a 5000rpm engine...  whaddya think?

RE: Cam profile design

nah, come to think of it, there are sbc-sized cams in slow engines too, with flat (crowned) followers

RE: Cam profile design

It's about throwing enough oil off the crank onto the cam. The 2500 to 3000 rpm I use to break in cams was all on SBC, so I have no experience with other applications.

When I hotrodded air cooled VW's, the boxer configuration with the cam below the crank, ensured plenty of oil, even at idle, so I guess it's horses for courses, depending on variable factors like surface contact area, oil supply, metalurgy, spring pressures, valve train inertia etc etc etc

eng-tips, by professional engineers for professional engineers

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Cam profile design

On the subject of cam profile design as it relates to making cylinder pressure and how this affects performance.
The single most critical element of the cam in this scenario, is the actual point the Intake Valve closes(degrees after BDC) When an intake valve closes, compression begins. Even though the piston may be moving up on the compression stroke, it wont start building the pressure untill the valve closes. It will be Hicupped back into the intake. The sooner it closes, the sooner it starts, and therfore the higherit will go. The sooner you close it, the more detrimental it will be to your goal of making this pressure build when the valve re-opens unintentionally from the valve bounce because cylinder pressures increase RAPIDLY with every degree of crank/piston movement. This also makes for a great hicup/burp into the intake. As I have said many times hence, it will also be the best recipe for murdering Torque and delaying the engines power making RPM range. It can be pretty detrimental to the overall health of the valve train, too.
Some realize this  problem from the Dyno's information.(I personally can hear it) Their only way to stop it is to up the valve spring pressure. This is a Band-Aid approach! To a point it is par for the course because the valve train weight must obviously be dealt with, and that is the way. After you have managed that, there comes a point when adding spring pressure to control valve bounce becomes rediculous. The cam may have a very high negative decelleration over the nose, or a high rate of seating velocity, or both. Therefore, I repeat another statement I have said many times:Throw that @$^*&@^ valve train wrecking camshaft in the trash!   

Have Fun!

Shaun TiedeULTRADYNE/LUNATI Austin,TX(stiede@ev1.net)

RE: Cam profile design

Question, the new cam shaft has lots of oil. In theory then, no metalic surfaces are then touching. So then what is breaking in then??????
I'm just trying to get the thinking wheels turning here. LOL

RE: Cam profile design

(OP)
Bearings normally operate under "hydrodynamic" lubrication where there is plenty of oil and nothing touches. The rotating journal actually pumps the oil through the bearing. Cam and lifters operate closer to "boundary" lubrication where contact can occur. Contact area is small and loads are high, so there is a high unit loading. Engine oils have EP additives to reduce wear under high contact pressure.

John Woodward

RE: Cam profile design

Agree, so then what is breaking in?
For metal to "break in" other wise wear in. It has to have contact. A cam lobe and follower represent a very high pressure contact point. What I'm driving at is if the cam and tappets lube just fine after the so called break in at low speed. Then ????  

RE: Cam profile design

There will be some wear in. The surface roughness averages are different from the lobe and the lifter. They will lap into each other. There will also be a pattern worn based on where the lifter is contacting the lobe. This can be influenced by lifter bore angle, and wether or not the cam is in a thrust plated block, and therfore wether or not the cam is walking back and forth in the block. Pre 1987 small block Chevies are a good example. WHen the cam is allowed to walk, it not only influences spark timing irregularities, it also reack havoc on the chain. THis of course retards the cam due to stretch, hurting low end power, cylinder pressure, cranking compression, exh valve to piston clearance, etc.

RE: Cam profile design

Way back in the 70's, I saw one turned by hand with the head of. As I remember, 4 pistons were at TDC at the same time, but I am recalling this to memory from over 30 years ago

Regards
pat

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RE: Cam profile design

Flat crank V8s have only 2 pistons at TDC at any time so 2 cylinders do not fire at once.

There are many current and recent applications of flat cranks. I made them for drag racing in Pro Stock and Fuel classes. They also had some flat cranks at HPD in 94 when I worked there.

Jonathan T. Schmidt
http://www.motorsportsdesign.com

RE: Cam profile design

Valve spring tech has certainly come a long way in the last ten years. I used to avoid designing some cams that were mostly ideas because I knew there wern't spring available at the time to handle the job. To an extent, cams have evolved from the advances in springs, too.

RE: Cam profile design

Shaun T do you do any work on any import/domestic 4 valves? Im in a crunch for some cams to a 3.0L v6 duratec by ford.   

RE: Cam profile design

I don't produce over head cams. The tooling  to manufacture is quite different. Let me do some checking.
The head could benefit from a trick 4 or 5 angle C.N.C valve job using a machine such as a Newen GII. The goal is to keep intake seat angles about .038 wide and exhaust about .060. Back cutting the intake may help too.  

RE: Cam profile design

Thanks for looking into it. From the way you talk it makes it sound like most cam manufacturers have NO CLUE on what they are doing.  Cat cams of britain has quite a few diffrent sets of cams for this engine but they are symmetric and the way you talk symmetric is NOT the way to go to acheive maximium power. They also seem to be pretty slow opening. THey come with a very hefty price tag of about 1540 + shipping dollars and they arnt built around your application. Further the duratec heads have a serious problem of overlap flow.  As seen in this SAE article http://www.bath.ac.uk/mech-eng/auto/txnet/983038.pdf

This makes me really wonder about if they got the cams right, because all the duratecs seem to suffer from severe overscavaging. Any help or recommendations would be greatly appreciated.

RE: Cam profile design

I guess I have made myself sound really Arrogant. I just don't have too high of an opinion of other cams. I feel that a product that has to be marketed to death with a couple of $Mill/yr shows it is inadequate. To some, I come accross as biased. I feel that is easy for one to think that untill he tries one of our cams. Then, the scepticisim goes right out the door.

Have you played wth the intake and exhaust centerlines of the stock cam? This is a dual over head cam isn't it? If it is, you can move both cams around in the motor independantly. This can help with scavenging. It definately effects cylinder pressure and cranking compression.

Symmetrical cams are a compromise.

Shaun TiedeULTRADYNE/LUNATI Austin,TX(stiede@ev1.net)

RE: Cam profile design

Iv thought about this but machining adjustable cam sprocket assemblies is pretty difficult.  Moving the cam a tooth is really unacceptable to be considered tuning. The cam wheels physically lock into the end of the camshaft so tuning this way is pretty hard to do.

Now on previous 4 cylinders they were held on by friction and they could be installed off center of tdc in either direction or they had a huge aftermarket like the zetec does and i had teh availibility of adjustables.

It seems like SOMEONE ANYONE could make 4 camshafts fit to my exact vehicle/specifications/mods for 1500 dollars. Its just a high price to pay for something that isnt exactly what i want.

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