Also, in case you're trying to suggest that not having a way for backpressure from blow-by to be relieved while under boost is going to cause issues... I really think that's taking it a bit too far.

It's the same conundrum you're in with a vacuum operated brake booster. Eventually you have to go back into vacuum briefly, or **** stops working. Same deal here. I'd bet you'd need to be in boost for several minutes without a single swing into vacuum for it to even become an issue.

Edit: OH lmao, and, if it got really bad, the pressure would escape the breather inlet anyway, as that isn't valved. So there you go, pressure can't really build up anyway. At least having the outlet plumbed to vacuum means you get a good purge of the crankcase every time you go into vacuum.

You get the same purge everytime you go into boost, as the crankcase is positive relative to atmosphere, with none of the pressure build up while under boost (which can actually be rather substantial).

I've not messed with this on a VHR, but just offering my opinion from the bit of experience I have with FI.


You can go pre-impeller and probably get something working, but that likely gets you into other issues.

Yeah it's not an issue. My subi ran the valve covers and crank vent to a AOS that vented to atmos. No PCV and manifold blocked off where it was running. Car ran 23psi without issue. Also what I loved was the valves and crank ran into the AOS, but the bottom of the AOS Tee'd back into the crank vent line so under boost whatever came out of the valves or crank, under vacuum it would all get drained right back into the block. This is how Crawford runs their AOS too on ken blocks car. This way its 100% maintance free and during a long race you lose no oil as a OCC will fill up leaving the motor with less in it.

The EJs are a completely different animal than the VQ.

It's only positive relative to atmosphere if there is, in fact, substantial blow-by. This engine is not like older examples where there is a mechanism at work pressurizing the crankcase with intake manifold air so that all you need is a single vent, it requires vacuum from the manifold to draw out said air. Without that vacuum, there is no evacuation of the crankcase, as I've said over and over.

And as I addressed in my reply, any true pressure buildup would exit via the breather, so that's a non issue.

PCV and crank vents work no different though :tup:

If you logged pressure in a VQ crankcase over boost, I bet you'd be surprised.

Here's one for you:

Crankcase Ventilation Mod w/Pics - Page 18 - MY350Z.COM Forums

but the system they are connected to is designed to be operated differently

Wow, 15psi got him a 1.5psi crankcase pressurization.. that's loose as hell.

with a drilled out PCV...

Not really. Bottom end of PCV goes to crank vent, other end has a hose running to manifold. Actually they're 100% the same as with every PCV system. When in wot the PCV closes so no air can enter the crank.

The boost to crankcase pressure curves look vastly different between the motors.

How? If the PCV is closed, boost can't get into the block and I thought that's all we're talking about. Only other way is piston rings and I don't think that'd be to different. Your motors rings seal or they don't.

Piston rings are never a perfect seal. That's how we get blow-by in the first place. It stands to reason that with boost coming into the pistons, a whole lot more blow-by will happen.

Yep.