im about to put a header onto my hatch and am aware of the B.S. cat situation that honda made for us dx guys. my question is if i put the primary o2 sensor where its suposed to go and then just let the other one hang would the car run like ****? or if i threaded another hole in the headerand got the second one in there also so atleast its snifin somthing....wich would be better?. im also aware of the secondary o2 sensor blockout chips for roughly $30...

 

If you can have it set to run on one o2 sensor then it would be best.

Your car will run like crap because the first primary o2 sensor will calculate and read the hydrocarbons/temperature before the exhaust fumes go to the cat and it wont be able to read how effectively the cat is working so it will be throwing a code.