An STi 2 way would easy, as you'd not even know, unless driving in anger.

Something more clunky, less progressive, like a Cusco MZ, or to a lesser extent, an RS maybe not. Not sure about the KaaZ and Qauife.

You'd want it to be as subtle as possible. Locked/Welded diffs have killed in the past so you'd assume they'd be all over it.

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Should have bought an STI