I replaced my old cheap ebay cold air intake with another one (Spyder CP-402) which has a CARB #, so I don’t have to keep swapping it out with my stock one each time I get smogged. However, I noticed the pipe diameter is smaller at only 2.5" compared to the cheap no name ebay one. Unfortunately, I can’t gauge the performance difference because I swapped it at the same time I did my B18C motor swap, and I sold my old CAI. I noticed the AEM 21-402 intake model is 2.75", so perhaps that is the ideal diameter? (I bought the Spyder brand because it was a lot cheaper than the AEM one, although now I’m having second thoughts).
So the question I have is 2.75" better than 2.5"? I would think 2.75" is better for more airflow, however I read somewhere a smaller diameter would give greater velocity to the airflow. Does anybody have a definitive answer to this? If 2.75" is better then I may just go back to a cheap ebay one and use my old CARB sticker from the Spyder intake.