All right, funlovin', along with everything else getting thrown your way in this thread, I thought I'd add some more, give you plenty of options to choose from. Give it a read.
http://www.flat6innovations.com/engines/performance-parts-a-services/5-performance-engine-modifications
I was actually discussing this thread with a buddy of mine (one of those VW boys
) and he more or less had this to say: He used to own a MkIV Jetta 1.8T, which tipped the scales at maybe 3300-3400lbs with him in it, I'd imagine. Now we're talking a front-drive sedan here, and he had it modified to put down about 230hp and 270lb-ft
to the wheels, and that thing was quick for what it was, and fun. there's no reason why you shouldn't be able to do the same with a car that's actually better suited to putting power like that to the ground and handle like a car with that sort of power, weighing in at maybe the 3000 mark.
Now while I couldn't give you any guaranteed numbers from the options Jake Raby elaborates on in that page, I can definitely say this would be a path I'd consider taking, very likely getting Boxster S power, and then some, from your stock engine for $5-6,000, and adding reliability and longevity to the engine on top of that. You get to bump your 2.5 up to a 2.7 and eliminate some of the trouble areas that plague these engines at the same time. Again, I know it's not 405hp, but an extra 60 or more horses in the same car would be plenty for me to have a whole new feeling of fun in my car, and you still get your roof rack, too. (To be honest, I've never seen anyone put anything on the roof of their Corvette, especially not a Z06).