Hi again Pengze,
I would definitly discuss this with the Engine Builders technical Department, just Google the engine designer to find their website and look for links to Technical Help, Service department, Installation or something similar, if you can contact anyone technical they will pass you on to the right people to help you. emails are free. When i have done this in the past I have always found people to be very helpful.
Should there be insulation on the partition between the air manifolds before and after the cooler??
If you modify the air inlet you will have to make sure that every part of the new manifold is larger in diameter than the old one, much larger if you fit any bends or elbows in it otherwise you will have an excessive pressure drop in the air manifold.
Do you have the correct air flow through the system? (Differential pressure across the cooler?? Turbine / compressor wheels cropped because of damage = reduced power? The faster the air flow the less heat will be absorbed by the air after the cooler.
What are the makers operating criteria for Tropical operation? Usually you would keep the air temperature after the cooler well over 40, nearer 50C to prevent condensation problems, when in the tropics.
Let us know how you get on.
It is always better to ask a stupid question than to do a stupid thing.