It is my understanding that you do NOT need the precat to pass emissions, as stated earlier it is in place for cold start emissions only. Replacing it with a down pipe not only greatly reduces underhood temperatures but your turbo's will spool more freely, assuming you will also go with a high flow cat (3 inch) and new cat back (also 3 inch)

 

Correct. Most states don't check cold-start emissions, where the pre-cat is used. You pull into a smog station with a warm engine, and get your testing done. Don't let the car stay overnight if you have a DP. A downpipe is worth every penny spent, but some **** states (i.e. Cal) have VISUAL smog inspections where they ensure that OEM smog equip is still installed on the vehicle. Lucky for us, most smog stations havent a clue nor the tech know-how on what is OEM on an RX-7, other than the main cat, air pumps, and O2 sensors.