2006 civic si performance parts?
 

where is the best and cheapest performance deals online? and what would be the better brand? and would you need to have a cat black exaust if you were going to put headers on? or could the headers just go with the stock exaust?

try ebay, ther is really no best part it all depends on what your prefrence is and how the car reacts to the part ,the same part on the same model could give more, or less hp. No one car is the same even though they are the same models