From their website:

We have devolved a complete line of LS1, LS2, LS6, L92 and LS7 all aluminum Small Block Chevy’s starting from 400 horsepower all they way up to 900 horsepower. These Engines range from 346 cubic inches all the way up to 440 cubic inches while only weighing 430 pounds. Even after installing a gearbox and radiator, these power plant’s still weigh less then most Lycoming or Continental 6 cylinder aircraft engines. Our GENIII LS series motors make on average twice the horsepower of most aircraft engines plus all parts can be bought new at your local parts store. All of our components are new and manufactured since the year 2000, nothing is used from the 1900’s. We have also worked hand-in-hand with a leading cam manufacturer to develop custom camshaft grinds tailored exclusively for our airboat engines. We have tested these cam’s on the dyno and on the water in our own boats. These custom grinds improve torque, horsepower, and yes, even fuel economy. WaterThunder Performance has also worked with two leading ignition system manufacturers to develop a reliable and tunable ignition system for our engines! If you want the weight of an aircraft with twice the horsepower we have the motor to meet your airboating needs.