-6 Header Selection, sizing Options

[jdogg]

When I did my -6 conversion a couple years ago, I did some wheeling and dealing on parts and ended up with a set of 1-3/4" headers which I am currently using on the bone stock 2.4T CIS motor. I have been fussing with it on and off the last couple years trying to make it run right from idle to 4500....it stumbles and seems genuinely unhappy until it hits the magical 4500 RPM mark, when it takes off and runs smooth as silk. After messing with timing, monitoring A/F ratio, checking for vacuum leaks, and much general head scratching, I got to wondering about the header size. I know the 1-3/4 that I have on there is rated for 3.0 and up displacement, but I didn't think primary size would have that big an effect??

So my questions are:
1- Will running a too large diameter header primary cause the symptoms I described (rough running from idle to 4500, smooth 4500-up)?

and
2- What size would be more appropriate for a 2.4T with CIS? 1-1/2? 1-5/8?