How does the stock plastic PI intake manifold hold up under boost? will it last under 8-9 lbs and will it last under 14 lbs?
If running F/I should the stock plastic pi intake be replaced? Or will it last?
Yup it will be just fine. Only reasons you would want to replace it are if it has cracked, or you want to have one ported for your set-up to make more power.
Mine lasted under 12 PSI of boost for over 50,000 miles until the coolant crossover cracked. It just gave me a reason to buy the new Trick Flow Manifold and get it ported out before i put it in. you should be more than fine with just 8-9 pounds of boost for quite some time.