It depends how much money you have, the more you pour into it the faster it will go. It aslo depends what kind of fast do you want, the straight line kind, or the kind that can go fast in corners. The easist way is to turbocharge the engine. Build the internals to handle the boost by replacing the piston, connecting rods, crankshaft and then lower the compression to handle the extra boost.Or change the engine to a larger displacement. For handling, an adjustable suspension will help as will better wider tires.There is so much to do, but in your caase, from the your question sounds, to make it go faster leanr how to frive better first. I have seen spec miatas with great drivers run circles on rich doctors with vipers and ferraris.