Okay. lemee preface this by saying I don't know anything. None of this is Hands on. All of it is my best guess, and attempts to be helpfull.
But, there doesn't seem to be alot of places to go on a Boxster for HP gains, let alone turbo. I'm including a few others just to be helpfull to the one place I found. GL
In 911 and Porsche World's 104 issue there is a Boxster that is running a 3.4 996 engine with Nitrous, and has 400+bhp. The site from the book listed as doing the work.
http://www.n2.net/wilsons/
In the August Excellence (I think, I don't have it right here to check) is Alios Ruf's 345 HP NA boxster.
And to answer the last, I looked all over for a Turbo on a Boxster, and could only find Gemballa offering a kit.
They are Gemballa.com for the address.
The concerns I have heard expressed for Turboing a Boxster mostly have to do with the engine. I think the only way to really know though is for more people to do it, and compare the resultes. I'd be very interested in it.
I'd also like to see if someone has Supercharged a Boxster. I'm more fond of Supercharging as a bolt on option, as I feel it fits me as a driver and person better than a Turbo.
Ed Hachtel
Porsche free for 2003!
(Yes I'm hoping to change that)