im running 3 inch on my primaries this question is up TO YOU! if you ask us, this WILL be an arguement , you like 3inch? go for it! you like 1 1/2 go for it! its your car, build it, make it yours!
I agree with Eddie, I run 3" and dump em out early for what I think is a good deep sound but that's only me.
do you know of a shop that does Mandrel at a reasonable rate? I was quoted 1200-1500 for stainless on mine, little rich for my blood