I was waiting for that chart before giving a rebuttal. The ramp on the cam determines when (in degrees) the valve opens and closes. Different rocker arms DON'T change those "starts to open" and "fully closed" points on the cam. The lifter is riding on the cam lobe and pushing up on a steel pole, it doesn't know what the upstairs neighbors are doing with it.
What the different ratio rockers do though, is increase the amount of lift, the same percentage across the board. So, instead of the valve starting to open an itty-bitty bit at first with a 1.5 rocker, it opens just an itty-bitty bit more with a 1.6 (and same for closing). I believe that's where the "perceived increase in duration" comes from.

 

I haven't given up on looking for it, my HVLP turbine arrived and I've been "playing"

Y'all don't know me but my posting history shows I wouldn't make up crap like that. I was surprised to see the chart and article when I read it. I just need to find it again. And, it was minimal but they showed it as changing.

 

before you waste all that time think hard about what is happening inside the motor. try to visualize it - in fact flatten it out in your head and turn it into a side-scrolling scene with hills and valleys.

as you go along, you ride up and down the hills and valleys. The lowest portion of the valley represents the time when the valve is completely closed. the lifter is riding on the back of the cam lobe. the peak of the hill is where the valve is completely open. now, you dont change the hills at all. instead, now you are walking up and down the hills wearing stilts (conveniently at a 1.6/1.5 ratio to your previous hight). The question is, do you now start moving upward as you come out of a valley any sooner than you did before? no. you dont. your upward progress begins and ends at the exact same times that it did before. this is duration, and it is uneffected.

the only way this is at all physically possible is if we are talking about duration measured at .050" lift in which yes - I agree with you whole heartedly that duration increases from this measurement. and that makes sense too. if I have to I can make a spreadsheet that will show it..... but I dont really know the best way to get it on here so that would be a PITA.

 

in for spreadsheet

 

alright, i made this up in an excel file to try to put this debate to bed.

The equation in a sine function based on the progression .001, .002, .003, ect... so then I took sin(progression), and used an if/else function to make any returned value that is < 0.0 = 0 (so any value between pi and 2pi will return a 0 rather than a negative number.) If this were to be cut and wrapped around a pole it would look very much like a cam lobe profile. the flat parts represent the sides and back of a typical cam flattened out and the bump is the lobe.
To get a ratio between a 1.5 and 1.6 rocker I took the original if/else function and multiplied it by 1.6/1.5 and plotted this against the original function.

I have all the raw figurative data here in my spreadsheet. and I can tell you that on this scale, at t=0 both lifts return a 0. at t=1 both lifts are positive. at t=3142 both lifts are positive (.000593 and .000632) and at t=3143 both lifts = zero.
this same thing repeats for the next opening and closing as well.

This is intrinsic to the math. the two lift patterns are tied by a ratio. which means that the 1.6 rocker will always have the same lift as the 1.5 rocker at any given time multiplied by 1.06667 (1.6/1.5). So any time the 1.5 system has 0 lift the 1.6 system MUST have 0 lift. Another way to say this is to say that ANY time the 1.5 rocker has a non-zero lift, the 1.6 will also have non-zero lift. if these two things are true than there can never be a time when one is open and the other isnt so duration must match exactly.

if you wanted to think of another example, think start and stop tests in cars. just to make it fun for this site. a mustang and a camaro must reach a set speed and stop. the mustang goes 0-60 in 9 seconds () and the camaro goes 0-100 in 9 seconds. then, by some freak coincidence, the mustang takes 9 seconds to stop as does the camaro. the duration for each test was an identical 18 seconds, but the camaro went further and experienced harder acceleration and deceleration.

now, since Im using hypothetical numbers (ultra diesel! with a 12 thousand second rotation cycle! cuz we all know those things dont need to spin fast to make power) lets say a nice and easy lift of .1 is going to correspond to the real world figure of .050". lets look at the data.

For opening times for each rocker system: the 1.5 hits .1" at t=102 and the 1.6 at t=95. For closing the 1.5 returns to .1" at T=3042 and the 1.6 at t=3048.

so the duration within .1" for the 1.5 rocker system is 3042-102 = 2940. The duration for the 1.6 rocker system within .1" is 3048-95=2953. From this point of measurement the duration appears to have increased, but this is a duration defined as "practical duration" assuming that only negligible air flow occurs below .1" or .050" for a real application. That may be rooted somewhere in some research or science, but I am not sure.

anyways, I hope this has clarified the situation.

 

Spec, the one flaw in your comparison, is you're more apt to fall on your face when on stilts, that's not necessarily the case with 1.6 rockers.
And if it helps with your spreadsheet data, the popular way to refer to cam duration is @.050. That way was established years ago so that different cam manufacturers would be on a level playing field when comparing their duration to others.
And to put duration in it's simplest form....it refers to the number of degrees (in crank rotation) the valves are off their seats. Rockers can't change that physical aspect of the cam, that's determined at the lobe.

 

i know the .050 thing, just didnt know why, but I used .1 in my data cuz it was easy for me to see. there was too much rounding with .05. my graph has x-axis units in some sort of weird radian thing, so I just called it "time" because time is easy to understand. I could go in and hit it with a constant to get it on a 360 degree cycle but that would be a pain lol. but yes, if i were to be more exact I would have given the open and shut numbers in degrees.