NefMoto

Hello all! I am planning to install bi-turbo on my 3.6 FSI BWS engine with two water intercoolers. And I am confused what cooling water system is right, and what is wrong)

I prepared sketch of current atmo cooling water system (I have separate cooling system for DSG) in attachment and two variants of planning cooling system. What variant is better and why?

Air to water intercooling is very inefficient.
It has about half the efficiency for the same area because the heat has to be transferred twice.
But the biggest issue is that the fluid is very prone to heat soak turning your intercooler into an interheater. Even the OEMs are not able to solve this issue, you won't either.
Run air to air.

Unfortunately, the layout of the car and stock-looking-car concept does not allow installing a front-mounted air-air intercooler or a like-APR air intercooler in a sandwich (I have genuine APR intercooler from previous project). Therefore, the optimal solution is to use a water cooling system from BMW x6m with a thin intercooler installed in a sandwich and two intercoolers under the hood.

It is not the optimal solution.
Find a way to run a FMIC or maybe even two SMIC's.

That will be much better.
BMW intercooling on that car is absolutely horrendous. IAT 40-60C even with cold weather outside.

Or just run a generous amount of WMI and no intercooler at all. That will work just fine.
Just have the ability to kill the boost when the WMI is out.