like an F15 fighter jet on the runway?

I have an aftermarket air filter on it, and I recently replaced the fan clutch. But this thing is loud! My 350Z (same size engine btw) creates a beautiful growl but doesn't have anywhere near the loud, whirring noise that comes from the engine of the VX...

... that leads me to another question.

How does Nissan get 75 more horses from their 3.5 than what Isuzu produces? Is it mostly in the computer? Would remapping work? (If it can even be done)
I'd love to get a little more power, but since the supercharger is no longer available, and turbo kits are more of a piece together, it seems like choices are quite limited.

any idears?...