ITR diff will not work in an S1 as far as I know. A quaife is good and reliable, if you don't mind extra maintainence then the Kaaz is also good but I wouldn't run the Kaaz on a turbo car. The cusco is also a clutch type. Basically all the common aftermarket diffs that I know of are clutch types with the exception of the Quaife.
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Don't bother giving me "rep", I won't return it and I think it is stupid.
Gracie Barra Clearwater
Gyms in Clearwater, St. Pete and Port Richey
pm me if you are interested in trying a free class at any of the gyms.