better, idle smoother, and increased the MPG. I used Mobil 1 Syn. in the past but RP seems a little better for the same price. As far as weight, 10W30 in the summer and 5W30 in the winter here in Ohio so adjust accordingly for where you live. I think the regular RP is good enough for a car that is mainly street driven instead of spending $$$ for the racing oil (21).