Speed

lots. you can put on a set of light weight accessory pulleys, you could add a header, intake manifold, throttle body, fuel rail, ignition box/controller,

also if its a manual a new clutch and lighter flywheel will add about 30 hp feeling to the "seat of the pants" dyno. in reality its still one of the best bang for the buck mod when it comes to hp gains. basicly anything you can do to reduce the rotating mass of the crankshaft will improve engine responsiveness and increase power output

If you want horsepower bolt on parts will do a little bit but not alot though... intake exhaust headers will probably gain you all together about 10HP. D17 is a hard engin to produce alot of horsepower, if you dont want a turbo then you could biult the engin ( pistons, camshaft (if you have the D17a2, i havent found any for the D17a1)) swap is another option either K20 or K24 but you have to put down 7g's. theres a turbo kit for the d17 its around 3 g's its supposed to give you about 56% more hp at 6 PSI but with turbo application there is a possibility of blowin out the head gasket and maybe the Plastic intake manifold. take some time do some research but best bet is to pay the extra money and do a swap