I finished my exhaust manifold a little while ago and I used 2" ID piping. I know this is what you usaully use for a 13b. This for a streetported 12a using a S5 turbo. I'm starting to think that 1 3/4" would probably be a little better. Please post only if you know what your talking about.
Thanks Caleb

 

That size pipe will be fine. When I was trying to spool a TA45 on a 12a I used the 1 3/4 ID pipes for my manifold. I really dont think it helped that much. Im now using the same manifold with my T66 and I seem to have the same boost response as others I know that used the 2 inch pipe.

 

leave the 2-inch pipe alone. shift your focus elsewhere.