Can you add a second turbo to a 98 mitsubishi eclipse spider gst or would it make more sense to go with a bigger one?

I'd probably opt to go with a larger one..otherwise, you'd have a twin tubo, but one of the units is older than the other. Let us know how it works out...I'd love to add a turbo to my Mitsu Outlander 2.4L 4 cylinder...not sure it can be done with the CVT auto tranny it has though.

Just get a bigger one.

you need 2 in series close to manifold, then 4-6 remote turbos in the back. You'll be kicking some major ass then.

Some cars have a small turbo that spools up quicker to decrease turbo lag at lower RPM's. As the rev's increase, the larger turbo provides the boost.

The both will produce the same amount of power depending on she PSI of the to turbos. The larger turbo will would seem like the better answer, but the twin turbo will give you your boost much faster than just one larger turbo.