i was gonna pay a place to put one pipe coming off the header to the rear where my new muffler would go.....is that good or bad to run just one pipe no cat, resonattor or anything, just the pipe from the header and my apex'i N1 muffler?

 

i was wondering about what size pipe is best? i mean people do 2.25, 2.5, i've even seen 3" lol

 

2.25 is best....so you won't lose back pressure. You prolly seen 3'' on a force inducted car a one w/ a larger engine than 4cyl....