Hi i'm going to be buying Doug Thorley headers for my 87 samurai and was wondering which is the best setup for this header? some say 2" pipe  is good others say 1 3/4 " for back presure. also which exhaust combo( cat back) has the best deep sound
out  there ?I'm looking for great performance and sound .

I have 2" on my 86 Samurai with a magnaflow muffler and it runs great.

I havnt seen a commercially available exhaust that addresses both sound and power. Your choices are limited, stockish sound and power, or an obnoxiously loud fart box. Custom is the only way to go. I would grab a 2" pipe kit and a Dynomax VT muffler(2.25" inlet/outlet). This allows for back pressure where needed when at low rpm's and cruising without sounding raspy or droning, while still opening up fully during WOT to allow maximum scavenging and peak whp.

Are you running a cat?

Got DT and 2" on mine. Loud and fast. I think I have the magnaflow (PO installed).

Talon's got the idea...

Absolutely running a cat, a spun mettalic core Magnaflow. It actually provides the same restriction as a straight 2" pipe.

cat should elimate the smell of the exhaust fumes  right. cause it does smell strong fumes with bikini top on .

It doesnt remove all the smell of exhaust fumes, but does remove the obnoxious sulphur smell.