Dry sump plumbing - cylinder head oil

What is the optimal connection for cylinder head and turbo oil return in a dry sump system?

Using another scavenge stage or just dumping into dry sump pan will work but are there more optimal ways to do it?

In the crank case there is a lot of blow-by so the oil has to be separated before going into external oil tank.

Is connecting oil return from head directly into the pressure stage or having a scavenge stage that will pump directly into the external oil tank (bypassing the AOS) possible?

In short, and I recommend you do further research.

It depends,usually having the head and turbo' drain into the crankcase is fine, but in some applications the head(s) may be scavenged and low, or rear, mounted turbo's may need a scavenge mechanism, usually with a small sump.

To work properly, there needs to be "air" in the area being scavenged to carry the oil droplets and mist through the pump, this mixture of oil and "air" to carried to the reservoir/external tank where it's separated.

i don't understand what you mean in the first part, scavenge pumps return directly to the tank, with the pressure pump drawing on the separated oil.

Sorry, I was a little confusing.

Usually, scavenge pumps are connected sequentially. Meaning that oil with a lot of blow-by (from crank case) and without blow-by (from head and turbo) are mixed.

My assumption is that it is possible to unload the AOS by connecting head and turbo sections directly to the tank and only crank case to the AOS.

Or, to connect head drain directly to the pressure stage as a source, since it's a tall and narrow compartment (see the pic) just like the external tank.

They are normally made as a series of individual sections joined together, witht he scavenge in parallel.

Normally, the scavenge pumps have enough capacity to be very close to, or even exceed, the blowby - as such, you are quite likely to find the AOS is letting air into the engine. By controlling how much is allowed to enter, a partial vacuum can be formed in the crankcase which reduces windage losses - you can buy fixed and adjustable "breathers" to control the level, usually around .7 to .5 bar. You need to allow some air to enter the engine because the air carries much of the oil. The other reason you need to be carefull is crank, and other seals, are intended to keep oil in, and may let dirt and other contamination in because they seal poorly in the reverse direction. Some will fit seals the wrong way round, because of this, and some companies offer double lip seals for some applications, which work in both directions.

I don't understand what, and why, you're suggesting that?

Oh, you don't generally need to drain the head(s) unless there is a known problem, such as high lateral "G" loads and horizontal, or "V", type engines. With a conventional in-line the air entering the "breather" and crankcase depression will 'pull' the oil down. Some wet sump engines that have a lot of blowby can have problems with oil drainage from the head as the blowby gases are moving against the direction the oil, reducing the oil returning to the sump. This can also happen with "V" engines and is a leading cause of low oil pressure at the top end, and destroyed engines.

You may be wondering how the blowby and introduced gases are removed, this occurs in the tank/separator where the gases are removed and vented to atmosphere.

Thanks Gord! I used get the whole system wrong. Not sure if I understand it completely, but it's much more clear regarding this question.