Wow...Dinan has a lot of potential there....If I were you I'd cut out the rest of the large pipe facing the incoming air right up to where it meets the small pipe...more air = better, right?
Does the inside gradually converge to the small area pipe? This would be good for compression, but if the large area pipe just ends and theres a hole in it for the small pipe, you're going to get get stagnation, which isn't very efficient...