They get the engines and parts free from their sponsor, Go Power Sports .
They would need a sponsor to supply them with American engines. A Briggs Animal or WF would be nice.
I don't know to many people that would spend their own money on a 4 engine Go Kart with 4 torque converters just as an experiment. They use what they get for free. I like watching their videos. I hope they continue to make them.
They did use some 5 hp Briggs engines on their Radio Flyer hot rod wagon
Danford1