Not all catch cans are born the same!
When I was 17, I tore off my "pancake" air filter from the top of my Pierburg carb, and fitted a Pipercross. I was the king of the college car park. Problem was, I now had a stray PCV hose. I stuck this in an empty can of Stella. That, ladies and gents, is your most basic form of catch can and nothing bad will happen. I did many many miles, and apart from an oily mess in a can that you have to empty now and again, no discernible difference.
Nothing to stop you doing the same. Plug up your inlet manifold + inlet ducts of all the PCV connections, throw all the PCV stuff in the bin and vent to atmosphere. Easy and cheap.
Also, as an added bonus, crankcase emissions are not part of the MoT.
For a more boring answer, read on...
Our internal combustion engines are designed to have a slight negative crankcase pressure (aka vacuum). This has the following benefits :
a) the oil seals work better, seal better and make it that bit harder for oil to escape. This is especially true of O-seals like crank and cam.
b) the pistons have less resistance on the down stroke and stop acting like a massive air pump. Marginal I know, but engines are proven to be more efficient with negative crankcase pressure as there is less crankcase air to push about. Air has a surprising mass - just stick your hand out of a moving car window to imagine what a downward piston has to act against at 5500rpm.
PCV venting to atmosphere will have a slight positive crankcase pressure due to piston blow-by, as the trapped air struggles to find its route to freedom - all with the pistons thrashing away.
Because of which, the downsides of venting to atmosphere is a very very
very small loss of power and an increase in MPG. You'd never in a million years notice, I know, but it's there.
All engines have their own "catch can" really, called the oil separator. This will be full of baffles and coarse wire catching the oil particles and letting it drain back down into the sump. The benefit of a
vacuum fed remote catch can is that all this caught oil (full of contaminants, acids, fuel vapour and condensate) is caught remotely meaning better quality oil in the sump as it doesn't drain back. It also makes for a cleaner inlet manifold too. Factory oil separators on the engine tend to be very compact - whereas a remote catch can is able to be much larger and more efficient.
This is all fine when you have vacuum. Cranna has a naturally aspirated F7R(?). I don't know if his system is vent to atmosphere or still vacuum fed.
If you want to maintain a vacuum fed crankcase, then turbocharging gets more complicated. This is because your inlet manifold is rarely in vacuum apart from over run. I think you are a turbo Optimistic?
The B18FT PCV system is much maligned but it does three really clever things :
1) It can regulate a maximum vacuum value (not allowing
too much vacuum, via a controlled orifice).
2) it has a one way valve function for when the inlet manifold changes from vacuum to boost.
3) its multiple path - so when the inlet manifold is in a boost condition, it changes the PCV route to ahead of the Turbo.
You can do the above three things all with commercially available Audi parts for the BAM engine. One day I will do a "how-to" but I feel slightly guilty giving advice when I haven't done a single road mile with it all!
Venting to atmosphere is fine, but it's just not cricket
