because i already had the manifold. i wanted to run the hyperpac with the turbo. for wow factor and because that intake designed to run in the rpm range my motor is set to run in. and it looks cool. there is no reason that i can think of as to why you wouldnt be able to get 400+hp with a 2bbl though. could probably get more but the openings in the stock 2bbl manifold will become a limiting factor eventually. not sure when that would be but they are pretty small.
