What do you mean you want more intake flow? A K&N is a low restriction filter so it should flow slightly more air thru it. But it can also allow too much debris get tru if you don't keep the filter oiled. I've heard good and bad about K&Ns so be careful.
With a turbo diesel, there are other ways to increase the air flow. Your engine's turbo is mostly responsible for air flow. To gain more flow, you can reduce the bottle neck effect of the exaust. Unlike gas engines, diesels do better with as little backpressure in the exaust system as possible. A larger diameter down pipe will help it breathe better.
Without knowing which turbo you have, you can probably change the turbo housing to a more efficent model or you can go all out with a high performance turbo or install twins. With these you'll get the air flow you need and then some. With increased air flow, you can turn up the fuel to the engine for impressive power gains. (When I mean impressive, I mean make a 454 Chebby look like a small block, impressive)