The om617 is capable of putting out a lot of oil pressure and if ignored during a turbo upgrade, you risk damaging that expensive new turbo. Below is information on the engine and a source for documentation so you can verify it on your own. If doing an upgrade, use a regulator or restrictor. Restrictors are a cheap way to go so long as you don't restrict flow too much and burn up your turbo.
om617 Service Manual: http://content.benzforce.com/45857036-MERCEDES-W123-Serv-Manual-Engine-617-95-TD.pdf
Service Manual Engine 617.95
Lubrication is section 18
You can find the manual at the link in the comments below
All page numbers I give are 18.8-500/#
- Minimum oil pressure (idle) - Min .3 bar (4.4 PSI)
- Minimum pressure under load: 3 bar (43)
- Oil pump relief valve will open at 7 bar (101 PSI)
- Differential pressure between the contaminated and clean side of the filter - 3.5 bar
Parts to consider:
- Turbosmart Oil Pressure Regulator
- Blue: https://www.benzforce.com/collections/universal-turbo-accessories/products/turbosmart-opr-t40-turbo-oil-pressure-regulator-40psi-blue
- Black: https://www.benzforce.com/collections/universal-turbo-accessories/products/turbosmart-opr-t40-turbo-oil-pressure-regulator-40psi
- Turbosmart fittings: https://www.benzforce.com/collections/universal-turbo-accessories/products/turbosmart-opr-4-an-fitting-kit-clear