Never heard of a turbo charging
kit for the 4-108.
You probably have the wrong compression
, the wrong injection pump and a bunch of other obstacles to turbo charging
Looks like the boat builder
or previous owner put the wrong engine
in your boat.
That being said, the 4-108 has been installed in a number of 40+ fot boats and several owners have complained of the engine not delivering the goods.
It is rated at 51 HP at the crank shaft at 4000 RPM
Useful power at the prop shaft at cruising RPM
is a lot less.
(I run mine at 2100 RPM, no soot, least fuel
burn and happy compromise of speed, noise
Perkins makes a 65 HP diesel
that may be better suited for your application.