My roommate had a ported GSR IM on his LSVTEC. It was ported all the way through, and where the butterflies are. He didn't get bigger butterfly valves though. As far as flow, I think the skunk2 IM would probably flow better at high RPM than the ported GSR manifold. Why get components that produce high end power, and not match it with the intake manifold?
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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
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