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
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
Thanks,
John Woodward
RE: Cam profile design
RE: Cam profile design
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
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
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
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
Specifically, what do you want to know?
RE: Cam profile design
RE: Cam profile design
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
and another with a demo http://www.soft-engine.com/pagine.web/inglese/cams0.htm
RE: Cam profile design
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
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 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
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
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
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
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
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
RE: Cam profile design
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
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
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
Shaun T ULTRADYNE Arl,TX
RE: Cam profile design
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
RE: Cam profile design
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
not form pulverized needle bearings. TYPO, sorry!
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
Thanks,
John Woodward
RE: Cam profile design
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
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
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
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
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Cam profile design
Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)
RE: Cam profile design
RE: Cam profile design
Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
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
RE: Cam profile design
Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
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
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
RE: Cam profile design
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
I love this stuff!!
Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)
RE: Cam profile design
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
RE: Cam profile design
RE: Cam profile design
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
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
I'm just trying to get the thinking wheels turning here. LOL
RE: Cam profile design
John Woodward
RE: Cam profile design
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
RE: Cam profile design
Regards
pat
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Cam profile design
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
RE: Cam profile design
RE: Cam profile design
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
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
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
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.