I'm pretty sure its still legal.
Aftermarket Turbos are, but thats because they're not tuned to factory standards.
Alot of cars are Turboed, like Chevy Cobalt and VW Beetle, even Acura NSX, which I think has a dual Turbo.
in cali anything you do to your car, depending on the cop you will get rolled
My tint (15% on rollups!), no front lisence plate (everybody does it), and driving with interior neons (footwell cathodes) is all ILLEGAL. But I haven't been rolled for any of it.
As far as illegal, try not to get side rollup windows tinted too dark. Make sure your Intake
has a Carb sticker. Your exhuast can't be too loud (TSRM is the sound limit, no Kazuma!!!
). If your soundsystem is too loud you can get a DTP (disturbing the peace) slip.