It's a multi-chambered design to ensure that it breathes well though at the same time, doesn't let any oil out, even when there is a lot of blow by. It has a drain into the sump, via a 1 way valve.

Could running without the valve help reduce blow by in the top end?

Not knocking your setup, just thinking out loud/learning.

I had to put the valve in the drain line because the crank case pressure was throwing oil up from the bottom of the can, and causing leak issues at the top. I plan to put a second breather hose onto the cam cover at some point in the future. I did it on my old ST185 and it worked well. This set up has been working well for a while now. No issues.....

Ok, thanks for that. I'm toying with the idea of a crankcase vent so interested in setups.

It can't hurt. Just make sure that it is plumbed into the top of the can where your baffling is. I highly recommend that you drain the can back into the engine. It's a no maintenance solution. 😎

I've already had a can fabbed. It's a series of cylinders that routes the flow up and down through the chambers. It has a drain it the bottom. I was going to simply return it to the sump next to the turbo drain.

It's currently breathing to the intake but I might vent to atmosphere.

I like the idea of maintenance free. Cheers.

BEAST! Watching this and Robs thread!

The car now has an exhaust, so the dyno tune comes next after I have wired up the intercooler pump and resolved a couple of other minor things.
I'm very close now!

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The car is now ready for a dyno tune. The CRD dyno is broken at the moment, so I may need to wait a couple of weeks before I can book a slot. I just hope that it doesn't have any issues. I'm worried about that more than what numbers it will push out.
If it is good on the dyno, I will book in a practice day at SMP or WP and see what it can do. I will be running the same suspension, brakes, wheels and tyres as what I ran at the last MR2WPC, so it will be a good comparison.
It's going to be a bit daunting, though also lots of fun to have decent power!
I won't predict here what I will have, though I only had 226kW at the wheels with my last dyno run. 
Fingers crossed....

That's great news mate.