Changing the camshaft by itself will have no effect on power output. A diesel engines power is determined strictly by the amount of fuel that is injected into the cylinder. If you want more power, I suggest that you buy another car or maybe transplant a turbo five cylinder into yours. If you did manage to increase fuel flow the proper amount for the added flow of the camshaft, the increase in power would be negligible.

Unlike a gas engine increasing air flow allows you to safely inject more fuel to make more power. In a gas engine the fuel and air are mixed when they enter the cylinder, thus increased airflow means that fuel flow is also increased in one way or another for the engine to run properly.

Have a great day,