Saw a website that was interesting. They build and sell pressure washers that have two engines with two pumps running in a series that doubles your GPM when both machines are working. I'm assuming the pressure doesn't change, just the GPM. I have my reservations, none of the rigs I saw was belt driven, which I would think would be a must for that kind of machine. Does anybody have an opinion on these machines? Kind of neat, if it works.