The earlier models had a bit of a transmission problem, I think ( not that I know much about engines). But my 2008 Passion was VERY slow off the line; I had to really calculate when I was pulling out into traffic how long it would take to get up to speed. My 2016 Prime that I bought just before Xmas is MUCH faster at accelerating and definitely smoother at high speeds. I travel a lot of tollways and regularly have it up to 80-90 mph with no concerns. I love it!