The stock H-pipe is 2 1/4". The Mac catback will bolt up fine. However I would replace the factory peice of junk with a 2 1/2" off road h-pipe. That will make you car scream up top.
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87 GT, 4 inch cowl hood,17x9 Cobra R's/255/45's,GT-40 heads,long tubes headers,h-pipe,Flows,BBK cold air, Mass air,70mm MAF, 1.7's, 1" spacer,underdrive pulleys,Pro 5.0, King Cobra, Adj. fuel Reg., Lakewood Lift Bars,50/50's,subframes, 4.10's.
Best time 13.012
Best MPH 104
Best 60' 1.816
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