What are your goals? What type of car do you want this to be. I mean sure two 4-barrles can give you more power as long as the rest of the engine is built to use that amount of fuel.
Most tests have shown that open headers produce more power than any full exhaust system but who wants to drive around like that all the time? A full dual 2.5 inch system should sustain that motor. Make sure and throw on some quality mufflers (as far back in the system as you can).
There are a variety of cams to give you different amounts of power at different RPM's. But again this falls under the "what are you going for" category.
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