||11-30-2009 11:56 PM
If you locate it before the cat by (or close to) the 1st o2 sensor (the one that is threaded into the cast iron neck) your technically to close to the engine and it will burn up the wideband (that is what I read, although the discussion seemed to be tilted towards HP V8's). I tried to get info if it would be possible to locate the bung around the 2nd o2 sensor (the one located in the SS canister, but ahead of the cat supposedly). This would be better heat wise, but it may be to far out of the exhaust stream to give you a trusted reading. That leaves only a location after the 3rd o2 sensor (down by and right before the flex pipe). The issue is that you will be trying to read your A/F minus the A. And it is noted that as the cat ages the A/F reading will change. It is not possible to thread another bung into the cast section (I checked with some folks who would know). therefore, the best that is possible would be to have a SS 'cone' made with a bung that would position the wideband 02 sensor deeply enough into the SS canister and before the 2nd o2 (and after the 1st o2) and in such a manner as to negate the effects of the volume increase of the canister. To do this properly will require a sacrificial exhaust manifold that you can dissect to determine the proper points and dimensions. Most folks just go with putting it near the 3rd o2 (down by the flex) as it is weldable and accessible, and make a mental note that the reading is off by a few points.
Have fun with it. [wiggle]