my buddy tells me what i need for my 2000 si is a HKS cat and dc header... then go from there what do u think.

 

Well what do you want? A hks cat seems pretty useless, it'll be too expensive and you can achieve the same thing with a actual high flow cat from ebay for $50. The dc headers not bad, but a airmass or comptech may be better and a intake. whats your budget?

 

what else is done to your car? I'd do suspension first. if your motor's stock id just keep the stock exhaust. sounds nice and quiet

 

if your car is stock...do the typica i/h/e setup. THEN you can go from there.

and it would help if we knew what your future goals were for the car...such as hp numbers and budget.

 

nitrous, and plus if your motor is stock ? you'll be getting great gas milage