I am currently having a 457 lsx built for my 03 silverado ss. I currently have pacesetter LT with 1 3/4" primaries and 3 inch collectors. At this time 1 3/4" primaries are the biggest available for my truck. I am wondering if custom headers with maybe a 1 7/8" primary or even a 2" primary would be benifitial to me. I am thinking they would, but I am also thinking that maybe the 1 3/4" primaries will give me more back pressure creating more torque to get my 5,300lb beast moving. I just want to make my truck as fast as possible. Any help would be appreciated. Here are the specs on the motor:
LSX block
-LS7 heads (stock intake side, but the exhaust has been reworked by WCCH)
-Ported LS7 manifold (jeremy Formato)
-4.200" bore
-4.125" stroke
-6.125" rods
-Custom CP pistons with a reverse dome of the ls7 combustion chamber
-SCR of roughly 11.2:1

 

Mother of god thats a big motor

Back on topic, the backpressure is great down low but over 3000 RPMS it will be a limiting factor. look for a custom header but that is some big bucks

 

Oh **** man!! Get some big *** stepped Kooks. Those Paces are TINY!!!!!!!!!

 

Stepped kooks? Thay make a stepped header?

 

Yes they do. QUIK has some on his truck. Although its a 2wd.

 

definitely some stepped headers fo that monster....

 

I though quick made his own headers out of f-body headers. Also, what are you guys suggesting? A 1 7/8 stepped to 2"?

 

is that 457 going in a 4x4 also where you from because i want a ride when that things fireing

 

Its going into a AWD silverado ss. Fly out to california and you can have a ride.

 

You said "as fast as possible".
I would either get a stepped 1-7/8 to 2 or just a straight 2".

I used to run a 461 inch big block in a truck with 2" headers and they worked great. With that many inches torque is not an issue.

I assume money is not a problem with this build.