you should get a K&N cold air intake, bout 200$ but it adds about 20 or more HP, you can also (depending how much financially and time wise want to get into the car) can have the cams and valves adjusted to take advantage of the natural hp(Faster accelaration)
i think a turbo is a bad idea because it will fry pistons and rings, maybe not immediatly, but it will shorten the life tremendously, you have to beef up aloooooot of stuff to be able to safely and effectively add a turbo, factory turbos are the best generally because they take all of that into consideration.
Another option i have seen for some Porsches is a bigger bore kit, it adds a litre to size, and makes a 4.6 litre engine with 490 naturally aspirated HP. Im not sure about the longevity of it though.
He came dancing across the water
With his galleons and guns
Looking for the new world
In that palace in the sun
On the shore lay Montezuma
With his cocoa leaves and pearls