yes, bolt on's do a lot for a motor if you need them. i.e. you have cams, valvetrain, ported/polished head, intake manifold, etc... with a stock D16Y8, they won't do s h i t, plain and simple. if anything, they'd change the torque and HP curves, and not always for the better. i'd be surprised if you got more than 5 or 6whp on the top end from that $1,000. they're a great investment if you plan to build your motor in the future, but not something to buy if you want to create more power on a stock motor.
no offense, i'm just stating the facts.