Originally Posted by Andy
The secondary O2 won't throw the ECU into limp mode? My friend had a '97 (or '98, I forget) ITR and he put a test pipe on and got the CEL. Everytime you were around his car you could smell fuel and it seems sluggish. He ended up getting a custom testpipe made with a welded on pipe the O2 sensor screwed into. It wasn't actually in the exhuast flow but strapped to the pipe and thermal wrapped to keep it up to temp and the CEL went away. His car run 13.9 with just an I/H/E and some good driving. He's running a Hondata system with a turbo now.
The car shouldn't go into limp mode, but there's always exceptions. Test pipes definitely make the car smell awful, but there's no real way around that since you're getting raw exhaust that hasn't been cleaned up by the cat. There are exhaust components that have a smaller inlet that the secondary o2 sensor fits in to more or less "trick" it into thinking that a cat is present. A friend of mine has a test pipe from Buscher racing on his EVO with this feature. It's pretty neat, but I don't recall seeing anything like that for a Honda/Acura, but whatever your friend did worked out fine.