How much will adding 16 lb to my car affect ET/mph(rotating weight)

Rotating weight has more more effect on acceleration than static weight. The further the rotating weight is from the 'centre', the greater the impact it will have.
David Vizard's research has some examples.
In his A series engine book, taking 1lb off the f/wheel was equivalent to taking 17 lb off the weight of the car. A formula is given to calculate the numbers.
Using a Mustang as a test vehicle, the moment of inertia was reduced using lighter wheels. The static weight that was removed as a result of the lighter wheels was added to the car, so that static wt did not change. Result was a 1/3 of a tenth in the quarter mile. Full article is in Feb 06 issue of PHR.