I have a Backwater SWOMP Lite kit on a 420cc predator...thinking of upgrading to the 670cc predator. But was wondering if simply upgrading size will give me much more performance.

Currently, the 420cc is modded, turning a 9x6 prop and will not exceed 3900-ish rpms in the water with this setup. Speed around 18-19. I assume that big prop (for that size engine) is what's limiting my max rpms.

Thinking a 670cc would give it more torque, but not really much more to offer since it's governed likely at 3600.

Is it worth messing with?

I have a 22hp Predator in a Go Devil frame and can't get more than 4,000rpm spinning a 9x6. The only time I think you would see more speed is if loaded Heavy where he 22hp torque could make a difference. You will definitely have to zip tie the governor spring to get more out of it.