635. i have both one works great in one app an the other works great for something else. I have a little toni with a jett 91 in it. This thing screams an i love it. I have a funtana with a saito an i love it swinging that big flat props. They both have there place. Now if all that was reverse, it would be like going to a top fuel drag race an watch a car go 330 mph but sound like a lawn mower doing it...........