R U A LS1

Hear me out on this one.
I was thinking if there is an area where a bigger exaust or duration wouldn't matter because making one bigger would do the same thing. OK.
Lets say you have a gallon of water with something shaped like a valve to cover the opening. Now let say you push it into the bottle ONE INCH to let some water out for 5 seconds (the duration) and it lets 1 pint out. Now you push the valve in TWO INCHES but for three seconds. For numbers lets say it lets 1 pint out of the bottle also. So i come to wonder, why would you want huge lift and less duration, or more duration (because i know a lot of power is made with more duration, but a lot lopier idle) and less lift, if as seen is my example i kinda made up representing what i was thinking, it doesnt matter which one is bigger? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Every time i think ive learned everything therer is to know about cams, there is always something else, as i think it's like that for everyone. Heck, you can be the CAM ENGINEER at a auto corporation, a whole department for cam development.

Phil

You pritty much want too go with, the duration you need too make power. In your RPM and for your application.... Just adding more lift too a small cam would add more power sometimes.. however you don't change the very critical Intake closing point... the Valve timing dose not change (from point too point)with a change in lift. since these timing event is what makes power. just increasing the lift is not the same as increasing the duration.

The lift is free which is what your examles show.

only thing limiting you from puting as much lift as possible is the heads ability too flow at those lift and the springs ability too controle the valve. At those lifts.

Brent
AKA Onemonkey
too lazy too change log on.

Old SStroker

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by R U A LS1:
<strong>Hear me out on this one.
I was thinking if there is an area where a bigger exaust or duration wouldn't matter because making one bigger would do the same thing. OK.
Lets say you have a gallon of water with something shaped like a valve to cover the opening. Now let say you push it into the bottle ONE INCH to let some water out for 5 seconds (the duration) and it lets 1 pint out. Now you push the valve in TWO INCHES but for three seconds. For numbers lets say it lets 1 pint out of the bottle also. So i come to wonder, why would you want huge lift and less duration, or more duration (because i know a lot of power is made with more duration, but a lot lopier idle) and less lift, if as seen is my example i kinda made up representing what i was thinking, it doesnt matter which one is bigger? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Every time i think ive learned everything therer is to know about cams, there is always something else, as i think it's like that for everyone. Heck, you can be the CAM ENGINEER at a auto corporation, a whole department for cam development.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">To answer your original "is there an equilibrium between lift and duration"...yeah, sorta, but not as you pictured it.

The valve is always moving when it's off it's seat. It doesn't snap open to a max lift, dwell there then snap shut like your example.

The amount the cam can move the lifter (and therefore the valve) per degree of cam rotation is the normal physical, mechanical limitation of a valvetrain. Call it "velocity" expressed in inches (of lift) per degree of rotation. This limits how much lift you can get with a given duration, so with more duration, you get more lift. You can stop here, or go on for the boring part...

The area thru which air/fuel mix can flow is basically the diameter of the valve seat times the lift. Call it "curtain area". Let's say the intake seat is 2.00 dia.(makes the math easy). At .050 lift, "curtain area" (CA) is 2.00 x .05 = .1 square inch. At .500 lift it's 1.0 sq inches, or 10 times as much, so much more air flows at high lift.

If you were to plot the valve lift vs. cam (or crank) rotation you get the typical curve which starts slowly, then rises rapidly to a peak the falls about the same as it rose. The important thing is the "area under the curve" which represents how much flow area you have. More area = more flow. You'd think that instantly opening the valve, holding it at max lift for a while then instantly closing it would be good. The lift curve would look like a square or rectangle ("square wave" is what it's called). That might work for producing power, but physcially it can't really be done. Things would need to be almost infinitely stiff and forces would be almost infinitely high...both of which aren't practical.

So, we are stuck with the type of motion we now have on cam operated valves. Of course you know that when you increase duration of both the intake and exhaust valves to get more "area", there is more overlap or time when the exhaust is still closing and the intake opening. Increased overlap degrades idle quality and low rpm power production because it lets exhaust back flow into the intake and actually pushes the intake charge back. However, overlap generally increases high rpm power production because the air can't stop and start fast enough to go the wrong way. Air is funny; it takes it just about the same time to stop and start at 1000 rpm as it does at 6000 or even 18000 rpm. We have to live with that.

I hope all that wasn't too confusing; it's just the tip of the iceberg. As to being a cam engineer, there is SO MUCH more to this than you might ever believe. The best cam guy I know was educated as a particle physisist, or someone who works with "atom smashers" to discover how things are in the sub-atomic world. That, along with a great sense of engine design and a genuine love of cars ("Gearhead") makes him so good. He'd probably say he's been "lucky". Having virtually all of the top 20 engines in the Daytona 500 run your cams isn't "lucky", it's being good.

My $.02

<small>[ August 22, 2002, 04:47 PM: Message edited by: Old SStroker ]</small>

R U A LS1

i understood all of that. and now i have a pretty good idea of how to read cam graphs. Although i still don't get the term ramp rates, or ramps, one of those. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> Is that exactly what you were saying, how fast the curve peaks?

Viper

iTrader: (6)

WOW, cool discussion. Keep on adding more; even if it's not for novices, someone may actually do a search on this thread on day.

One Monkey

The ramp rate is what makes one 224 cam diffrent from another. 224 cam.

lift has alot too do with it... but it's possible too have a cam with say 224 duration with .550 lift have as nice a ramp as a 224 duration cam with .590 lift.

The ramp rate is just how fast the cam takes too get too peak. It's has alot too do with valve train tech.

But back too your original Qustion... you can't tune a cam for a paticular setup just using lift!!

you will need too move your duration.

you can use lift too make more power... (or less) but it is very rare too change where the power is made by changing lift.

Brent
Speedaholic
Engines & cylinder heads.

R U A LS1

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Viper:
<strong>WOW, cool discussion. Keep on adding more; even if it's not for novices, someone may actually do a search on this thread on day.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">TTT for ya. Maybe someone will add. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

ONE MONKEY: but wouldnt a ramp also depend on how much power the cam is making and how fast the motor revs. Because if the peak in my car is at 6000 with 4.55s, it would take a heck or a short time to get their in first, (just example) and the peak in another car with the same cam with 3.23s would take a heck of a longer time to rev to 6000. Faster ramps related to drivetrain, motor, everything, etc.? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

SStrokerAce

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by R U A LS1:
<strong>i understood all of that. and now i have a pretty good idea of how to read cam graphs. Although i still don't get the term ramp rates, or ramps, one of those. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> Is that exactly what you were saying, how fast the curve peaks?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Ramps = the angle of the flats on the lift portion of the cam lobe. The faster the ramps the faster the valve opens. A fast ramp has a steep angle on it.

As for the Duration Question:

"So i come to wonder, why would you want huge lift and less duration, or more duration (because i know a lot of power is made with more duration, but a lot lopier idle) and less lift"

I like to have as much area under the lift curve as possible for the application. So a Low Duration high lift cam vs. a big duration low lift cam is what I would be after. Most people don't get that it's total airflow, which your example illustrates perfectly.

The reason people like duration is because they want to have the valve open during the peak tuning pressures at the end of the intake cycle. A intake manifold actually creates a supercharger like effect as the valve is closing. (If the cam is chosen properly) Most poeple want to keep the valve open here. I feel that fast ramps on a lower duration cam with high lift and placed in the right spot (Lobe centerline angle) relative to these tuning pressures is much more important. Sometimes you even want to slam the valve closed as fast as possible. This ramming effect is also why low lift flow helps out so much. Remeber that lower duration numbers (in turn causing smaller overlap on the same LSA) will help out low end torque, due to the fact that you have a higher dynamic compression ratio. This gives you the extra torque to get you to the higher rpm HP faster. This gets really compliucated, but you are on the right path. Low duration, High lift. IMHO.

The problem is that the high lift will eat valve springs. That's one reason people don't do it too much. But then again a fast ramp with a longer flatter peak at a slightly lower lift will have more flow area than a lazy ramp with the same lift.

Keep going. I'm sure that Old Stroker will have some more stuff to say on this too.

Bret

Old SStroker

A few thoughts on "ramps" measurement of duration, etc. (This isn't short!)

We may be getting confused on nomenclature here.
It is intuitive for some to think of the generally straight, rising portion of a cam lobe as a "ramp". Unfortunately, that's not exactly correct. Call it the "flank".

I believe the "ramp" area of a cam is that portion which is the transition from no movement in the lifter to the rapid movement up the "flank" of the cam (and the same thing at closing). With a solid (mechanical) lifter, there is some clearance ("lash") in the system which has to be taken up in the initial motion of the lifter to prevent impact. With any lifter system, you need to gradually load the system, not smash it in the teeth with a ball bat.

My try at an analogy: Visualize a steep driveway approach, say 45 degrees, which goes up 30 feet. If the driveway intersects the road at a 45 degree angle, your car will probably take quite an impact if you try hitting it at any speed at all. In fact, the front valance or spoiler will scrape or dig in. Now blend the 45 degree slope to the road with a gently increasing curve to about the 5 foot high level. No scraping and little impact as you drive up. The "ramp" is the transition area you added. Unfortunately, many folks call the rest of the driveway aproach the "ramp" which gets confusing. Remember we called this the "flank".

If you were to measure the length of this 45 degree, 30 ft. high driveway, without the transition "ramp" it would be 30 feet. Your transition "ramp" might be an additional 20 feet long, but it only got you the first 5 feet high.
Now what is the "duration" of the total driveway approach? 50 feet? Sure, but the effective part is the 25 feet that get you the last 25 feet high.

Because different cars have different approach angles (think lifter size or design) and different suspension stiffnesses (think hydraulic vs. solid lifters), the transition ramp varies greatly in length. So, to compare one driveway approach to another, let's measure it after the ramp when we are on the working part (45 degree portion in this example; the "flank"). It's similar in camshaft nomenclature.

When most folks quote cam durations of 210, 220, 230 degrees, they are referring to the ".050" duration of the cam lobe. That is the duration starting when the lifter(not necessarily valve) is .050 inch off it's seat until it's within .050 in. on the closing side. In other words, after all the transition ramps are cleared. That ".050" duration combined with the lift, determines how the cam performs. That makes more sense, because some cams, especially low performance factory cams have very long ramps, and if total duration was quoted, the 210 degree (@ .050) cam might actually be 300 degrees total, but only the 210 degrees is doing much valve opening/closing.

More on the driveway analogy: to get to a given height (lift) in a certain distance (duration) you have to change the steepness. At some point your car won't be able to climb the slope because it's too steep for the traction available. That's the limiting factor in your driveway design. It's called "velocity" (inches of lifter movement per degree of cam rotation) in cam terminology as mentioned in my earlier post, and is the usual design limit. It doesn't depend on your car speed up the driveway (or engine rpm in cam talk); it's basically traction. (Not perfect analogy, I know)

What others have said in the thread is good. We compare cams (and driveways) by how steep and how high they are. I guess having a "bigger" driveway might give you some bragging rights in your neighborhood, but it might not be the most effective one. So, too, with cams.

My highly opinionated $.02.