I replaced both of my upstreams this past weekend along w/ a full tune up. WOW! They make a difference. We did both O2's, plugs, wires, fuel filter, pcv, oil change, and air filter in 1hr 45min. But we were hussling! lol

98 Ford Contour SVT - No mods 02 Suzuki GSXR 750 - No mods needed lol