I knew this was a mistake.
Nothing to see here,

Has the intake charge stopped moving and is now being pushed back out of the cylinder via the intake port (reversion) before the valve is closed? Or are we trying to time it to prevent that? How much of the intake charge has escaped out the exhaust during overlap? What about using the timing of events and head design to "supercharge" a NA engine beyond 100% VE? Wouldn't/doesn't measuring the volume of air entering the engine vs the displacement x number of RPMs over a period of time give you some type of calculation?

Engine RPM and atmospheric pressure have to play a part in this.

This stuff fascinates me and I wish I had gotten involved in the physics of it when I was younger. Nowadays I just deal with what is happening behind the flywheel.

People who get it, Pro Stock and high end NA engine builders and tuners, get all my props.

what gets [confuses] me, is the "4 degrees advance ground in" claim on the cam description.
why does this get published, and do you then advance it another 4 degrees after you dial in the cam, or leave it there ?
i know i get "cornfused" easily because the spiders have cobwebbed my ol' noggin', but this deal gets me every time, no matter how often it's explained to me.
please help an old dumazz like me understand this better !

If they say that, take most comp cams XE series mopars as an example. The cam is ground on a 110 LSA and is installed C/L at 106. All things being correct, if you lined up dot to dot, the cam should be at the 106 centerline. The grinding of the core is adjusted to make the installed C/L at 106. Sometimes they are spot on, sometimes not.

The cards I've seen the last 35 years have the timing events for where the cam is to be installed. In the above example, the Comp Cams card numbers would be representative of the 106 ICL. If you move it from the recommended installed C/L, then make adjustments when using a DCR calculator.

Lunati card, cut on a 110 LSA install at 106. Numbers on the card are for the 106 installed C/L.

He's the only one on Moparts I have on ignore.

I guess when a statement is made that when using the cam card info you have to adjust the timing events for advance/retarded installs that are ground in. If you move it make adjustments, pretty simple. The card has the correct timing events on it in most every case as evidenced by the lunati events being at a 106C/L. Smart guy but just wrong on this one in most every case regarding the info on the card and being used in the DCR calculator. Add 21 to both sides of that lunati intake event, still comes out to 106 ICL.. I dunno.

Sorry to wreck the thread. I was hoping for an intelligent conversation. It is (was) a great topic.

Were my questions too stupid?

Nope your question was good - the alleged boffin can't hold a conversation without taking his ball and running away!

Apparently, the content was beyond your comprehension, hence your hissy fit.

Certainly not, your comment was well founded and appreciated.
However, (in my opinion) these factors are always present and relevant to the question of cylinder fill. The reversion question has too many variables to be reduced to anything more specific than a trend, not amenable to math.
I had a much narrower scope: only the changes between "official" timing figures, and when the actual intake valve closure occurs. I had to actually do the calculations (I wrote an .xls to do this) before I knew there was any substantial change.

and now for the "stupid old man question of the day"....................
as [a ground in advance] the cam is ground on a 110 lobe center, and is to be installed at 106 [supposing the "dot-to-dot" markings are correct], the question : is valve to piston clearance factored in any way when these cams are ground ? if not, what happens if the valves opening cycle[s] are too close or too far from the piston, and if these are not correct, how do you fix this without choosing another cam ?
i am up front in disclosing the fact that my engine skills are limited, mainly factory builds using a slightly warmer cam at times, but i like to learn things. even at my age, where i may or may not, use what i [possibly can] learn and put into practice.
please don't be too hard on me for being this way. i should have started this learning curve many years earlier................

Isky use to sell valve (not sure if they still do or not ) notching tools for increasing the width and depth of the valve pockets in the pistons in the motor for 3/8 and 11/32 valve guides. The tool had a round shaft that went through the valve guide with a square tip on one end and a cutter that would fit into that guide, using an electric drill motor on the guide would make the cutter notch the piston tops
I ended up marking the guide with tape above the valve guide the amount I wanted to increase the valve notches, IE .020 to ? to whatever was needed

thank you for that tool illustration.
what radius would one want on the cutters ? .030 ? more ?

I thought I made one showing the lathe bits wider apart to create a relief larger than the valve, but I can't find it.
In some engines with large stem incline angles, the valve's vector is not linear w/r/t the piston dome (since the piston is moving). The valve head will scuff sideways as the piston goes down, so the relief should not be a larger circle but a "stadium" (1/2 round both ends, parallel sides).
I'd like to see a 1/16" radius (unless it becomes too thin), and this should be radiused on the dome to remove the edge. This helps flow in & out of the reliefs during OL.

A normal cam is ground with the intake valve opening BTDC and the exhaust valve closing ATDC the same number of degrees. Look at the Lunati cam events above, and you'll see that the intake opens at 15°BTCD, and the exhaust closes 12°ATDC. I'm assuming there's a half degree rounding error, and I think some of the events are in cam degrees, and others are in crank degrees, just to make everything even more confusing, but you can see that the events are moved forward of where they would be if they were both the same number of degrees before and after TDC. The numbers they publish are what you should measure if you degree your cam in and everything is within spec. My speculation on why they do this I feel are purely for marketing reasons--putting a bandaid on a poorly designed cam, and this isn't done because the cam companies don't know what they are doing, but because hot rodders don't know what they are doing, and the cam companies don't want their products getting bad mouthed because someone purchased a cam too big for the application. They want a big cam because it's cool, get one that's too big, has a soggy bottom end, so they advance it to give a little more bottom end. If you know what your motor wants, you can surely take the advance out.

the cam companies don't want their products getting bad mouthed because someone purchased a cam too big for the application

This^^^

thank you.