Just like the title states what size of header should I use. I will be buying a d-1 procharger and Gt3 cam for my stock ws6 in the near future. The only problem is that I want to remain emissions friendly and would like to know if i should go wih kooks 1 3/4 or 1 7/8 header with ramdom tech cats. I will also be buying an slp ls6 intake which comes with an egr adaptor which I hope will help with emissions. Any help greatly appreciated...

 

As far as emissions goe's i see no differance in 1 3/4 vs 1/78 if they are both using a catted y.
Me personaly i would go with the 1/78 with a catted y with set-up you have described.

 

Thanks Mike.

 

I would go with the 1 7/8 and the catted y pipe for emissions

 

nick's not ganna like this , but just go with coated pacesetter, save yourself $400