[cobracrazy]

all very good advise, here's more:

if you must use slip fit collectors like most of us, try some exhaust heat wrap to reduce the leakage common to slip fit setups. Like mentioned above, that leakage will affect the quality of the information the sensor collects. If you're going to weld bungs, weld an extra bung while your at the welder. That way if you have it dyno tuned with a wide-band you can compare results with your ECM.