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Cam design basics ?

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Cam design basics ?

Postby Unkl Ian » Tue Jul 03, 2007 1:31 pm

Can anyone suggest a website that covers the basics of cam design ?

I know it's a full time job trying to come up with the "perfect" design,
I'm just looking for some general guidelines,based on displacement and rpm.

Thanks.
Ian
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Postby Cammer » Tue Jul 03, 2007 3:03 pm

http://www.harveycrane.com/

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Re: Cam design basics ?

Postby OldSStroker » Tue Jul 03, 2007 6:11 pm

Unkl Ian wrote:Can anyone suggest a website that covers the basics of cam design ?

I know it's a full time job trying to come up with the "perfect" design,
I'm just looking for some general guidelines,based on displacement and rpm.

Thanks.
Ian


Ian, I believe you mean "specifying which lobes from a library of lobe designs should be used and on what centerlines they should be located" for a given engine, rather than design of a new lobe profile.

Different "cam designers" use different methods of determining valve events, duration, lift, etc. for an engine. I have not come across a website which details how the successful ones do it. My guess is the more successful cam specing guys are not going to tell you how to do it.

It is my opinion that many folks who spec. cams rely on past experience with given engine combinations and change duration, lift and centerlines and perhaps lobes from their baseline. They may then have a cam made and run it on the dyno or at the track or both. If it improves the torque/power of the engine it may be used and recommended. If they use the "design/build/test" method, time and money determine the number of combinations they can look at.

Too often folks want to simplify a complex subject. They may want to break it down into a couple of variables like durations, ICL and LSA when in fact there may be tens of variables effecting the outcome. Almost any empirical "Rules of Thumb" (ROT) of cam design (as opposed to lobe design) only get you close to what may be the optimum cam for a given engine/vehicle combination. Some ROT are a whole lot better than others.

The engine or engine/vehicle combination ultimately tells you if it likes or dislikes a cam. I see the problem as explaining why a given cam works better or worse than another. The engine knows why, but we can only speculate based upon our understanding of how things work. I see a remarkable parallel with how men relate to the women in their lives.

All of the above is leading to this: try to learn and understand as much as you can about how IC engines process air (and fuel of course). Some of it is very basic physics, but not everyone looks at the basics. Much of it is more sophisticated in practice but it comes back to basics of Mother Nature. People like Gordon P. Blair have written extensively on the subject. Blair's stuff, while not an easy read, is quite good, IMO.

Hey if it were easy, everyone would be a "cam guru". I'm not, but I have met a few I consider good. In those cases they all had a fairly good understanding of Ma Nature. I have no opinion on their relationships with women other than Ma Nature. :)

My $.02.
Last edited by OldSStroker on Sat Jul 07, 2007 9:54 am, edited 1 time in total.
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Cam Design Information

Postby UDHarold » Wed Jul 04, 2007 11:32 pm

The advice given by Oldsstroker is as good as I could have given, and my general thoughts, to boot.
Cammer told you the only place on the Internet where you will find contemparary Ramp design. Harvey's site covers everything from 'Old School' to future art. Unfortunately, all the illustrations are of symmetrical cams. Most designers will mix-n-match opening and closing ramps.
Cam design is both an Art, and a Science. If you think of it as science and art, you have the HOW and WHY of cam design.
To apply the science of designing a cam lobe/profile(the HOW), you have to be very comfortable with algebra, and No, that is not what the Little Mermaid wore, and familar with differential equations. Airflow into and out of the engine depends upon differential equations. You don't have to solve them, but you need to know how they work.
The best way to design a cam is a subject arguable among cam designers; each one guards his methods(that's how he makes his living, after all!) while studying the other's techniques.
Harvey teaches you how, and gives you the necessary software, and that's how he makes his living now.
Which lobes go together, the LSA, and a few other things are the WHY of cam design. It is all empirical knowledge, meaning you taught yourself by trial-n-error, and interpeting the results. How good you can interpet the results determine how good you are. You had better understand engines thoroughly, and what the driver wants the engine to do.
This is all knowledge that you learn by doing.
An example: There are some cam companies that claim that Intake Closing is the most important event in a cam cycle.
I claim it is the 3rd most important event, beating only where the Exhaust closes.
My cams seem to be successful than those companies.

Just some thoughts on Cam Design.......

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Postby torquer » Thu Jul 05, 2007 1:15 am

ok conventional cam profiles with an unrestricted intake. I havnt come across a cam manufacturer that understands what happens when you put a 300 cfm restrictor plate under the carb. The usual theories go out the door.
The fuel curve changed to total opposite, lost 1000 rpm, effected by inertia, velocity changes of intake. Sensitive to cam duration and valve overlap.

How does a cam manufacturer take into these considerations when designing a camshaft profile.

How many engine builders rely soley on there cam manufacturer/grinder to give them a profile. How much emphasis goes into designing a profile.Its hard to put trust into something you outwork and is out of your control.

please your thoughts on this
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Re: Cam Design Information

Postby Rick360 » Thu Jul 05, 2007 8:40 am

UDHarold wrote:There are some cam companies that claim that Intake Closing is the most important event in a cam cycle.
I claim it is the 3rd most important event, beating only where the Exhaust closes.
UDHarold


Harold,
What order of importance do you place the events? Why that order?

Thanks,
Rick
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Cam Timing Events

Postby UDHarold » Thu Jul 05, 2007 11:27 pm

Rick,

I consider the intake opening and the exhaust opening points to be so close in equal importance, I do not know which is MORE important. Here are some thoughts:
The most important single degree in your camshaft may be the degree before the intake valve opens. At that point, the exhaust valve is open and closing, there is a volume of exhaust gases left in the cylinder, being pushed out the exhaust port by the piston. These exhaust gases have a positive pressure, known as back pressure. They cause reversion when the intake valve opens. The volume and pressure of the exhaust gases will determine how the cylinder fills on the intake stroke.
Proof? Most engine builders have tried 2 cams with the same intake and exhaust grinds, but different LSAs. Put both cams in the same engine, on the same intake center line, and dyno. Result? Two different power curves.
You say, but they were different LSAs! I said put them in on the SAME intake center line--Same intake cam grind, same opening and closing points, 2 different cylinder filling rates, 2 different power curves. The exhaust opening and closing points were different, though. The exhaust reversion/back pressure governed how the intake would fill the cylinder.

The intake opening point is important though. Different opening points of the same intake profile produce different power curves, also.
So I put equal value on both. The intake closing point is next, but different cam durations/profiles with the same intake closing point produce different results.

Some people say you have to lock the barn door before the horse gets out. I think you had better be sure the horse is in the barn before you lock the door.
With proper design cams develop high inertia ram on the intake stroke. If the air/fuel mixture is still entering the cylinder when the intake valve is closed, the engine will make excellent torque and horsepower.
The exhaust closing point mainly affects low-speed torque, and it's a TIME factor. At low speed the exhaust closing takes a lot more time than at high speed, and exhaust gases have much more time to do devilment.

As far as limited carburetion/restrictor plate engines go, it is more an Art than a Science, and a good deal dependent on whether or not headers or cast iron exhausts are used. My most popular cam for 500 2bbls with cast iron exhausts is the 272/278F108, 243/249 at .050, 155/161 at .200", .523"/.545" valve lift. They are winning a lot of races. With 500 2bbls and open headers, and light cars, I may go as big as 282/288F108, 253/259 at .050, 165/171 at .200, .550"/.552" valve lift. As far as 350-cfm 2bbls, I have a 266 I like, 237 at .050, 149 at .200, and .501" valve lift.
These profiles are all brothers, in the same design family and the only .842" tappet family that I make. The valve lash is .016". I of course have bigger cams.

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Postby Rick360 » Fri Jul 06, 2007 8:34 am

Harold,
Thanks for sharing your thoughts on this. :D

Always interesting to hear a point of view different from the crowd.

Rick
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Postby gimmemud » Fri Jul 06, 2007 8:46 am

I dont know what Udharold does different or why but it dang sure works. We called Harold and ordered a cam for a 555 bbc with dart 360 heads, this engine had a very reputable cam co. cam that was specd by them for this combo. With nothing more than cam change this truck picked up 3 tenths in 200ft mud racing. So what ever he's doing I like it.
Unpredictable Pro Mud Racing.


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Postby Cammer » Sat Jul 07, 2007 9:52 pm

I will give a little insight as to where cam design may be going:

http://citeseer.ist.psu.edu/37511.html

http://216.239.51.104/search?q=cache:oD ... d=13&gl=us

http://www.cl.cam.ac.uk/teaching/1999/A ... node4.html

http://www.cl.cam.ac.uk/teaching/1999/A ... node5.html

A little further reading:

http://www.audietech.com/Newsletter/CAMBiblio.htm

Cam design involves some serious knowledge!

As related in sites above, computers are a great help in cam design.

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Postby Danglerb » Mon Jul 09, 2007 4:26 pm

In my own search for basic cam design knowledge I'm pretty sure it didn't involve rotating any spline curves. As a end user isn't it more a question of ramp rates limited by rpm and materials, as much lift as I can have, and overlap tuned to the intake and exhaust manifolds?

Does my cam guy even need to know rotating spline stuff, or is it enough that the guy working on the cam software knows it?
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Splines, knots, and other such stuff......

Postby UDHarold » Tue Jul 10, 2007 12:03 am

Those articles are very interesting.
I have been using what they define as spline fits since 1980, when I dodn't know the meaning of the term. I just called them "Multi-Segmented Polynomials"(MSP), and all UD rollers, flat tappets, and hydraulic tappets have been of this sort since 1980. a very few have just 4 polynomial equations, most have 8 to 10. Until the late 1990s, I didn't even know that where I joined them was called a 'knot'----a knot being where you join 2 pieces of string together.
One of those articles either has words in in that I cannot even guess the meaning of, or else they are terrible, repeated, typos. It is like 'knot', words that have a meaning only to those familar with the terminology of the author.
These articles are like teaching the alphabet to someone who wants to be a writer----Necessary knowledge, but not the real output desired.
There may be dozens of workable cam design programs available, and all are like a toolbox to a carpenter, necessary to build your desired project. Some build mansions, some build doghouses, all use a hammer and saw.
None of the various cam designs programs really tell you how to design a cam, they just provide the tools to design cams with.
Knowledge and experience use those tools to design the cams.

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Postby Cammer » Tue Jul 10, 2007 9:28 am

Many of the websites I posted may contain overly technical content but the engineer in me feels certain members of this forum can use them.

We are fortunate to have members like UDHarold to advise us on camshafts.

Thank you Harold for your open and concise responses!

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Re: Cam Timing Events

Postby digger » Sun Jan 27, 2008 8:17 am

UDHarold wrote:I consider the intake opening and the exhaust opening points to be so close in equal importance, I do not know which is MORE important. Here are some thoughts:
The most important single degree in your camshaft may be the degree before the intake valve opens. At that point, the exhaust valve is open and closing, there is a volume of exhaust gases left in the cylinder, being pushed out the exhaust port by the piston. These exhaust gases have a positive pressure, known as back pressure. They cause reversion when the intake valve opens. The volume and pressure of the exhaust gases will determine how the cylinder fills on the intake stroke.
Proof? Most engine builders have tried 2 cams with the same intake and exhaust grinds, but different LSAs. Put both cams in the same engine, on the same intake center line, and dyno. Result? Two different power curves.
You say, but they were different LSAs! I said put them in on the SAME intake center line--Same intake cam grind, same opening and closing points, 2 different cylinder filling rates, 2 different power curves. The exhaust opening and closing points were different, though. The exhaust reversion/back pressure governed how the intake would fill the cylinder.

The intake opening point is important though. Different opening points of the same intake profile produce different power curves, also.
So I put equal value on both. The intake closing point is next, but different cam durations/profiles with the same intake closing point produce different results.



To test which of the four events is the most important don't you have to start with a specific cam and then change only one of the events at a time by the same amount and see which produces the most marked difference.

for example
35-70-70-35 baseline

40-70-70-35
30-70-70-35

35-65-70-35
35-75-70-35

35-70-65-35
35-70-75-35

35-70-70-30
35-70-70-40

From what i can see the proofs you give only show that the intake opening and exhaust opening have an effect not that the effect of these is highest or most important.

I have a 32-84-80-28 cam in my 12V I-6 street car to me this seems like an odd setup it produces quite low torque which i always though was due to the 84 degree intake closing event causing reversion out the intake port at low charge speeds lowering the dynamic compression thus killing lowend (the more convential school of though)?

The only other cam i have found that offers the same late intake closing is the following 62-82-82-62 and that would produce quite different results i would think.

Realistically the most important event probably changes depending on the particular cam and engine setup.
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Re: Splines, knots, and other such stuff......

Postby xenginebuilder » Sun Jan 27, 2008 9:24 am

UDHarold wrote:One of those articles either has words in in that I cannot even guess the meaning of, or else they are terrible, repeated, typos.

I think the one you are referring to is:

http://216.239.51.104/search?q=cache:oDS_qGLctsQJ:www.math.vanderbilt.edu/~neamtu/papers/nps2.ps+spline+cam+curve&hl=en&ct=clnk&cd=13&gl=us

This is a google translation of a file type "PS" or Postscript, and many words and all the equations are not translated. This is either a print capture or possibly a Microsoft "Works" file. For those interested in actually reading it, you can download the original and open it in a proper viewer. The native document "Evince Document Viewer 2.20.1" in my Linux box worked fine on this.

UDHarold wrote:None of the various cam designs programs really tell you how to design a cam, they just provide the tools to design cams with.
Knowledge and experience use those tools to design the cams. UDHarold


Amen!
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