I think the average non-turbo size is 2-1/4 for our 4bangers

I'm running 2-1/4 from the header to the cat to the muffler, then 2-1/2 from there (mainly because that's the only cheap turndown i could find locally, which is only about 14" anyway so that doesn't make much difference in my case <img src="/forums/images/graemlins/lol.gif" alt="" />

'84 PU low & slow
Central Valley Crawlers