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I have the safc II on my Z. Installed it because I was running rich and fouling plugs. I installed it myself but you need to get it tuned on a dyno at a competent shop. That's the only way to do it right. I don't know about gains, didn't buy it for that. Its more for making sure your a/f mix is good and being able to adjust it. The only other option besides dyno I can think of is to get a wideband o2 gauge and sensor to use to adjust it.