What part of the exhaust system is best to modify first?

Question

headers,resonator,cat,muffler?

Answer 1

The exhaust manifold, since that is the first thing the exhaust gases pass through when going through the exhaust system.  You can have a 3 inch exhaust and 1.5in. headers and it won't do you a bit of good.  Start at the engine and work your way down.