Ok, putting dual exhausts on an i4 robs the engine of torque because of too much exhaust flow and too little back pressure. Thats why its safe to stay single exhaust.

question 1: If you have a 3 in single exhaust. Is it equivalent to having two 1.5 in duals?

I ask because I want to put dual exhaust on my i4 accord that has a turbo kit. I have a 2.5 in exhaust right now. Most of the piping is going to be 2.5 in(actually until the axle at the back) Then I want to split it to make it dual exhaust. Perhaps 1.5 - 2 in piping.

Thanks for your thoughts.
Kosh