look Ill give you a good example: I had a 93 mustang coupe with a stock cam, 1.72's on the exhaust and and the stock 1.6 on the intake, 19 lbs injectors, CL 73mm maf, no tune, stock headers or if you dont like calling them that then stock exhaust manifolds, 160 thermostat, electric fans, timing bumped up 12 degrees, advanced cam 2 degrees, stock exhaust with no cats and a pair of 2 chamber flows dumped, no EGR or air pump, automatic turned to stick with 355 gears. The motor made much better torque at this point with a stock Cobra intake, no port work. 12.90 at 112 mph the one and only time I took it to the track 5 years ago because the knuckle heads I was smoking on the streets with big dollar mods (cam, heads, big injectors, 2.5 mandrel bend exhaust, X pipe, big dollar intake combos) utter over kill. motors were 7000 rpm screamers, could not believe that those mods I mentioned on my old setup could do just that. Again supporting mods can advantage a good free flowing exhaust but it is a science in which can increase or decrease low end torque or hinder high end HP. In any case which can be wide and varied for what I want at the moment a 2 1/4 dual or even a 2.5 Y into a 2.5 mid spliting again will give me little or no top end restriction on a stock 200 hp motor, all I am looking for is a sound, even a dual 2 1/4 would work for me.