Originally Posted by 01tj
What would it take to get a base 325xi or 328xi to perform as well as my 330i with the sport package? Could this be done by getting slightly lower/stiffer springs and more aggressive tires? I'd probably also add an exhaust and if necessary an intake.
You can do the 3 stage intake manifold conversion (basically putting a 330i intake manifold on a 328i). I've been thinking about doing it myself. You will need a tune to get the extra horsepower though. Here's a DIY with more info about it.
Handling wise I have heard many things on these forums. An inexpensive way to make your car more aggressive and handle better is lowering springs. Popular choices are H&R or Eibach. Some say that springs on stock shocks is not recommended but many forum members who have done this have had no issues at all. Many claim its just as comfortable as stock but feels way stiffer (in a good way) when thrown into turns. Another route is shocks and springs or coilovers. This is a more expensive route but has the best results. Those are probably the best way to go for suspension upgrades but if you are on a budget springs will not disappoint (based on what I've read).
I haven't done too much research on exhaust but based on what I've heard the BMW Performance Exhaust is popular along with the Active Autowerke exhaust.
Search the forums and you will find what you need to know. Your own research will help you get an idea of what you want. I hope this helps!