Riva.......
The Riva stage I, II, and III must be one of the most used mods in the United States. They are very popular and have a wide range of modifications to your watercraft. Their kits cover all aspects of changes.
For example, if you change the flame arrestor to a different type with less resistance, you'll need to increase the size of your jets (carbed models) and in your exhaust.....they include everything to make the change simple.
How much speed? I've never asked that question, so, maybe someone else wil chime in here. The Solas impellers are pretty popular also....:cheers: