SSAC's primaries are 1-5/8in, just like SLP's & TOG's. This is the common size, as it was the best fit our exhaust port outlet, and seems to extract the proper amount for our engine airflow.
PS's and ZZP's primaries are 1-3/4in, as were Xtreme TOG's.
There were also a very limited offering of TOG Big Dog headers with 2" primaries... only the 10-sec s/c cars of JohnT (MP112/spray) and the BadSSEi (KB blowzilla) ran these, as far as I know. I doubt many others even attempted them, as folks like Jamhoney (Gen V) have gotten to low-low 11's with TOG's and X-TOG's.
- Dave
