I have a similar set up as you. G3, F.I. h.f.c's, Stillen cat back, and with the UpRev tune on a Mustang dyno showed a gain of 11 whp, which came to 286 whp.
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Stillen G3|CBE|ground kit, F.I. H.F.C., C.F. fangs|mirrors|pillars, Hotchkis, SSR Type-F, RE-11, UpRev, BC BR coilovers
15% tint, LED black hdlts, color match handles, Dynamat, tail lt. tint, Mines C.F. frt. lip|rear spoiler, Amuse rear,skirts, vented fenders, c.f. vented hood, gloss blk. roof
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