I have a 1991 Toyota Pickup, Extended cab, v6, 4x4, 5 speed. Does anyone know what the stock exhaust pipe size is? I currently do not have time to check and I was just wondering cause I plan on changing whats on there the cat is the good the rest behind it is starting to leak (pipes and muffler).

 

1 7/8" I believe is stock diameter pipe. Stay small. Don't kill your torque curve.

 

Use all mandrel bends. 2.25" out of the header through a 2.25" cat and muffler. 2" tailpipe.

Preservation of exhaust velocity = better torque curve. And it seems a turbo style muffler works better than a straight through on these trucks.