The stock NA cast iron manifold and 'front pipe' is essentially a 4-2-1 exhaust setup. It is a VERY good design and layout. The deficiency is what comes after the merge of the twin pipes: the stock 2in pipe and system is too small.

This pic shows what I do to improve the flow from the stock NA front pipe:

...I cut off the 2in pipe at the merge of the twin pipes; and form and weld on a section of 2.5in pipe. The added pipe is short; so that I can smooth and blend things inside for smooth flow, using my die grinder and long shank carbide burrs.

...then I go 2.5in on back.

...and yes, that is a flex coupling sitting there where the catalytic converter would be located. It's a great place for the flex coupling; which is a required component in the exhaust systems I fabricate.