Many hundreds of thousands of miles, many track events, etc.. across many different vehicle platforms, and never so much as a hint of a problem, nor reports of damage from other enthusiasts so far as I am aware.
I think what this thread needs is a primer on O2 sensors and catalytic converters:
http://www.aa1car.com/library/o2sensor.htm
http://www.howstuffworks.com/catalytic-converter.htm
Note than on OBD1 NSXes their are only two O2 sensors, one per bank, and both are in fact positioned ahead of the factory catalytic converter on the header/manifold (primary).
On OBD2 NSXes, their are four- two per bank. One is again positioned ahead of the factory converter positioned on the header/manifold (primary) and one is just down stream of it just opposite the honeycomb (secondary).
On any OBD2 vehicle- the secondary sensor is their for but one reason- per Federal Law so that the ECU can verify that its reading is less than that of the primary sensor to assist with emissions check. Essentially, the ECU is looking at the relative difference in voltages, and if it is equivalent it can fire the check engine light to indicate an emission component malfunction- ironically usually a bad O2 sensor and in more rare cases a failed converter (not so much of an issue since leaded fuel went out of style). Note the stoichiometric point a/f calculation is a direct result of the oxygen reading from the primary sensor alone in most applications, as the oxygen reading is best taken as close to the engine as possible.
Once again, per many other threads on this topic- mitigating the secondary sensor reading via re-location or using an anti-fouler is all that is needed. On my last custom exhaust we put in a 1" diameter X 6" long L pipe which worked very well. Doing this will ensure that-
1) The secondary sensor on OBD2 vehicles reads less than the primary. This is neccessary to ensure that the annoying CEL light does not come on and more importantly the ECU does not revert to a fixed fuel map resulting in poorer performance/fuel ecconomy as is the case on some applications like the S2K. After clearing the ECU and running several cycles, a modern ECU will adjust to the new primary/secondary readings and likely be fine indefinitely.
2) The expensive O2 sensor does not get fouled over time (all applications).
In closing, as others have mentioned, their is a real difference between speculation and fact on any topic- so do include your sources when quoting. Some of the replies, and hp gains and dyno charts and car comparisons anymore are frankly getting comical- (e.g. like magic high boost test pipes of ever gain + 40rwhp). However, that is likely a different discussion for a different day. :wink:
