3" pipe sounds a tad on the big side. Sizes like that are generally for turbocharged and/or rotary engines. With turbocharged engines, the turbo itself provides all the backpressure you will ever need. Rotaries just plain don't like backpressure. I would guess somewhere in the 2.5 inch range would be more appropriate for your setup, but I'm no exhaust expert.

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
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"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson