Here's a few quick pictures of my Polaris Bellmouth (Polaris P/N #5410834). I bought mine on ebay for about $12. I can't comment on any gains from this specifically, but with the K&N, jetting and new pipes it really made the bike come alive.

This fits our bike perfectly in place of the very restrictive Triumph Snorkel.



2007 Speedmaster w/ SS Long Slash Cuts, K&N, Polaris Bellmouth, and AI Removed 132/42/2.0 Turns Out/No Shims