hmm, yeah, actually got calculations wanso see what pipe suitable for you, like myself, im using a 1.3 16V engine, setup of the piping i use trial and error wan
from engine => extractor 4-2-1 => 1.7" piping => midbox(straight flow) => mid box(straight flow) => 2.0" piping => muffler tip :D => out to atmosphere arleady...
sound okie larr....power, got larr, butthen car still slow bai... :( but not recommended if using auto larr...auto recommended using 1.8" piping for a 1.6 car, even with straight flow, still can have abit power :D go 2.0 inch only if you have manual :D
for 1.5, think best is 1.7/1.8 also kwaa, not much diff, butthen dun go 2.0 all the way, sure die wan.... :D
hope i never make you go koo koo, rreading my post..ahaha,i also dunno wether you guys can understand what i said also anot :P ekkekeke
and erm, if you want muffler, go for s-flow for more silent setup :D straight flow are alwiz noisy, normally larrr :D