what he meant by rebuild was to rebuild the engine. to upgrade the turbo means to change it to a bigger and faster one. Doing this will incur a lot of changes. to much air without caution will blow up your engine. one way to make your engine "faster" is to make simple yet calculated mods. Mods like I/H/E could have significant gains for your engine. wheel and tire combo will also be a factor.There are a lot you can do to increase/imrpove the performance of your 4d56 engine.