RE: make it faster?
Well the OS CV-RMx or one of my stage 1 modded Go Engine .18's would be your best bets, and both will definitely out perform the PB.18. The bigger issue is making the boat handle the power\speed. The PB hydro's are good First Time boats, and a lot of fun, until that Need For Speed creeps up on ya. It takes a bit of hull set up modification to get that boat to Stay On the water over 40mph.
You can upgrade your prop to a metal prop if you haven't already, an Octura Y535 is a good Starting Point.
You can Increase the Nitro% in your fuel and get a Quite a bit more performance.
If you haven't removed the shims under the head yet Do So, it will increase compression which will increase HP.
You can trim 1\4"in off the header and bend the tuned pipe Brkt. on the back to hold the tuned pipe forward more, the length of the pipe and header controls Max RPM's. Shorter means Higher RPM's
If you hope to do much over 40mph and Enjoy it, I suggest you look for something with a bit more modification room and suitable for higher speeds.