I live in a state where emissons is not required and I just plugged my tube in my MAC long tube Off-Road pipe. I used a bolt and a hose clamp, but this winter while it's apart I am welding a cap on the end. I did pass MD emissions with it plugged on a modified stock h-pipe that only had 2 cats, I made it fit my long tubes for emissions.
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My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98