with my BMC ever since I washed it with detergent and left it to dry for a couple of days, my TT can now hit 1.3 Bar again, whereas when I installed it new it limited the car to 1.2 Bar, unlike the 1.3 of the OEM paper filter, so whats the deal here ??? with oiling

Did the same thing thing with the BMC filters in my Stradale and washed without oil they seem to suck harder

 

Could it be as simple as higher air flow through a dry filter as compared to oiled?

Is there a measurement recorded of the particulate size (in microns) that can pass through the stock filter v. aftermarket filters?

 

The oil simply fills some of the space that air would otherwise pass
through. If you want to stop dust going into your motor, you need
the recommended setup for the filter.

 

for a given filter area, the basic trade-off is between flow and
effective filtration. You can get better flow if you don't mind
sucking in dust. I stick with the paper because it never loses
filtration efficiency and simple cheap replacement is the maintenance.
When I need higher flow, such as when/if I went to a bigger turbo,
then I'd do the EVO V-Flow setup (more filter area = better flow),
with a designed-to-be-dry filter.
Oil dries with use and will then open up some more area, but it does
it's filtration by acting like fly-paper, hopefully getting particulates to
stick to it rather than pass into the motor. As the oil dries and becomes
more dust-covered, more particles will just bounce off already-caught
particles and pass on through if they're small enough.
If you over-oil, there's a risk of sucking oil into your downstream
tract, gumming stuff up, like your MAF. All in all, I'd skip the oiled stuff.
Joe
Joe

 

I read a post some time ago where a guy did some tests with different replacement filters and measured airflow. It turns out the std OEM paper filter when NEW allowed more air to pass through than any other filter be it cotton or oiled, and the OEM filter filters out more debris than any other filter.
I think the OEM filter cloggs quicker though from memory.

 

right. Paper ones flow more when new, and get clogged because
nothing passes throuch, and some holes get filled up. So run paper,
and keep it fresh. Save your money, be happy.
Joe