Just installed my new friction drive unit and 4 stroke motor from thatsdax.com. So far....I am extremely impressed with this unit. It's *very* quiet and the torque this puppy puts out is way better then any 2 stroke I've owned. The instructions are very specific on break-in......the first 500 miles are to be ridden in a very conservative manner and the valves will also need adjusted occasionally. I am able to climb the same hill I would have to go 3/4 to full throttle on my 2 stroke.....the 4 stroke has *way* better low end torque-all I needed to get up and over the same hill with the 4 stroke was 1/4 throttle. I think this motor will fit my riding style very nicely, I'm not sure what the top end speed is like with this unit, but since I like to go about 20-25 mph most of the time-this unit is going to work very well for me. It seems to go 20 mph with the throttle barely cracked....it will be interesting to see what this piece will do once it's fully broken in.