I guess the questions are (1) do you want to make more power and (2) does the engine have enough potential to support the full airflow of 8 ITB's?? One easy way to see if there is more in the engine is too see what the MAP sensor is doing at WOT. If the readings stay in the high 90's kpa, then it is doing pretty well. If the MAP is dropping to low 90's or even high 80's kpa, there is a signifigant restriction and more air should help.
I agree that the dual 3" tube are about a 35% drop of potential airflow, but going to dual 4" openings will equal it out and still allow fresh cool air.
I guess if it were me, and not knowing the potential HP of the engine beyond where it sets now, I would prefer to have the dual 3" openings and fresh cool air versus 8 ITB's and hot engine bay air. Now going to 3.5" dual tubes brings up the potential airflow by 25%.
Best scenario with re-engineering and retuning is dual 4" tubes to a slightly larger but similar plenum for each side.
A few options for sure. Hope this helps Dave.
Mike Norris
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