The GSR won't fit the LS....and Random Tech makes terrible cats.
I'm looking at Catco right now, but I'm finding all kinds of conflicting numbers for the LS cat length...just gonna have to get under the car and measure the thing tomorrow.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
Team B.O.B.® - Ballaz on a Budget