How do they rank from good to better to best?

Does anything change with money put into them (headers, exhaust, intake, etc.)?

 

not again... how much money do you have to spend?

 

Not really looking to do, more for my own knowledge. I currently have the ZC in my CR-X and I have no complaints. In the future when my financial situation improves, I may consider a swap, but for now my ZC will more than do.