Here is a video that Jorgen found on YouTube showing the oil pressure on a EFI at startup.
Notice the bleed down rate after shutdown.
That's another way oil can enter the sump after the engine is shut off.
60 psi gauge.
https://www.youtube.com/watch?v=AjFrGtOBUGU.

Just curious is your bike mostly stock all around?

Has been discussed probably too much in this thread. It is important to note that vacuum in the air cleaner is totally irrelevant - because there isn't any to speak of. There is some confusion on that aspect, because when you re-route the breathers outside the air cleaner this also (sometimes) includes fundamentally changing the breather performance (larger holes and/or different umbrella valves) - possibly altering CC pressure - for better or for worse. But that has nothing to do with where the expelled air goes *after* it leaves the breathers.

By routing outside the A/C you've slightly increased your HP potential and slightly changed the amount of oxygen fed to your engine. That has its own implications, almost always positive. But this should not be confused with any gains/losses or ancillary results that are due to the modification of CC pressure from different breather mods.

You don't think there's an ideal CC pressure that works best for a given year of bike? It seems like it would hinge on case design (year), displacement (known), and RPM (same for any bike).

Or if you could measure net out-flow from the breathers, an amount of flow that's too much (for "any" bike) and signifies a problem?

Yes, that would be utopia to have a standardized method for measuring pressure and flow that "anyone" could do accurately. But I think it's worth targeting, isn't it?

I totally understand your concern that this is just a bandaid, but I don't remember the details or technicalities.

But, on the off chance that extra headspace is inherent in the design of the system (HD has actually recommended the lower level) then wouldn't it be important to rule out too-high oil level (wherever that be) as a cause for various afflictions? I mean, it is definitely possible to over-fill at some level, so at the very least it leaves the avg Joe some room for error.
(no offense Joe)

unless the air you can pass thru it is excessive. That's what we still need to work out - the blow-through test is subjective - but maybe it's still "explainable" enough.

Replacing them is cheap, and easy. I don't wait for spark plugs to totally fail before replacement, I put new ones in every year or so, depending on miles. If someone asks me how to tell if questionable spark plugs are causing performance issues, I say "replace them, you can always put the old ones back in later if you want". It's a simple answer that works even for the novice.

Replacement is not ALWAYS the answer (in fact it's possible to have new parts that are defective, compounding the confusion) but in most scenarios with the umbrella valves it's the best place to start.

I have available all the instrumentation one could ever need, and new vs old umbrellas, it's just a matter of doing. But I question the value of such testing on-the-bench. For one thing, the average Joe does not have precise instruments or expertise to perform the same tests, so it's not transferable. For another, my old ones aren't proven "bad" so even if I do get different flow/pressure readings, they're really not applicable and no threshold is established for what "bad" is. And for another, it would be a "static" test - I cannot simulate the pulses from the CC - and even if I could, see points 1 and 2 above. And even if all those obstacles were overcome, there could be other un-tested reasons for an umbrella not performing.

I think that actual running CC pressure and flow testing could be validated, but bench testing umbrellas seems too error-prone to be worthwhile. They are cheap and easy to replace on 04-up, and for other bikes it's only slightly more difficult to replace (or slightly more expensive to retrofit aftermarket).

Edit: I may still do various bench tests on the breathers if I get the opportunity (time) but I'm apprehensive to publicly share any results due to the confusion that may cause. We'll see how it goes.

I think the ideal CC pressure is subjective to the needs of the machine.

Racers need more vacuum for better ring seal, more power. Every Oz. of power gets you closer to the front of the line.
But that brings the inherent lower scavenging which also brings the need for a better scavenging system.
The 07 pump has been tried as a replacement for the (no longer built) Pro Flow multi-stage oil pump.
That's where the Karling Mod came from for the 07 style oil pump.
http://sportsterpedia.com/doku.php/techtalk:ref:oil05f

But street engines for the most part aren't looking for that last bit of HP, or at least their owner's wallets aren't.
So lower overall CC pressure at a point would require better scavenging.

The best scenario I believe can be depicted from bustert's slack tube testing.
I believe it hindges on individual engine setup / performance at the time instead of a cookie cutter option for a modification.
Their may be a higher or lower point that works best at certain RPM.
If you're riding mostly from 5 grand up, you're probably going to need more vacuum applied or lower positive pressure however that's achieved.
But another factor is wear.
What works right now may not in 6 months to a year.
And it would need adjusting.
What works for your setup with little blowby has no bearing on the guy with 175,000 miles behind him and is wondering what works for you when you don't have all that wear.
Him applying your setup to his engine may not work well or vise versa.
But for a street engine, 0-4000 does seem to be working with the OEM setup.
But sometimes it doesn't.
The optimum ratio seems to be a slight vacuum during normal riding conditions for a street engine.
We need to crawl first and define 'slight'.

I'm hoping rocket's testing can shed some more light.
That's what we need, more evidence.
The scenario seems to be that you can have a 'slight' vacuum with let's say medium CC pressure and you can have a 'slight' vacuum with higher CC pressure (as in the CC being bottled up, using bigger pistons etc.).
Bigger volume down means bigger volume up.
So two engines can have comparable 'balance even with non-comparable parts.

I wouldn't say worth 'targeting' just yet.
Worth testing, yes.

I totally understand your concern that this is just a bandaid, but I don't remember the details or technicalities.

All the more reason to question the practice until evidence is found.
If they didn't want the oil level to hit the top mark on the dipstick, why would they make the mark?
They suggest an amount of oil to use for an oil change.
They know better than we do that there is always going to be a certain amount of oil left in the engine peripherals.
They are covering their asses by not suggesting to run the oil level to the top.
Another reason to add a lower amount, run the engine and top it off.
The CC pressure buffer is above that mark.
They just don't want you to go over that mark based off their filling suggestions.
I really feel sorry for Joe.
He's probably a genius compared to me.
And he takes all the flack...... Thanks man. :)

That is my thinking as well.
The breathers are cheap but as mentioned earlier, they are not always easy to get to.
I can pull my tank, ignition and covers in 30 mins if I'm not in a hurry.
Some don't have as much time, convenience or ease to remove.
So it's not always as cut and dry as 'just replace them'.
I've got several old ones cause I'm the same way.
If the current ones fail, these old ones may get me by until I can get new ones.
But, I agree, the simple answer is just replace them.

Running the oil level less than full is not necessary and if you think you need to so as to keep from puking oil, you have issues.

Ok
on the 2006 the "breather bolts" have an .0625 orifice in each plus you have the 5/16" hose from the cam chest
Does not the aftermarket "horse shoe" or breather bolts radically alter the area available for the engine to exhale to while changing the pressure to force oil to the scavenge area ?

I was just thinking that would be a start.
Knowing where the values sit, then later possibly knowing what doesn't work well and then measuring the difference.
But that would also be some dependency on ambient temp.
Yes, there are people that don't have the luxury of even housing there bike at home.
Much less to have the tools and knowledge that we collectively are gathering.
I wish I had all those instruments you have, I'd probably starve from malnutrition from not stopping to eat. :D

It been our understanding the stock breather bolts with the small, restrictive hole on the head end was done so to increase pressure to aid in scavenging.

I'm not sure anythhing can be proved/disproved with all the variables in play.