Today's oils are so darn good it is just a matter of preference really. I use Valvoline 50 wt for the Gas Racers, unblown or Blown. Lake boats on Gas I use Valvoline 20-50 Blown or unblown. Blown Alcohol I use Eastern Kendall 50 weight or if I can't find the Kendall I use 50 weight Penzoil Racing oil (Penzoil Racing is totally different than other Penzoils). The reason for the Kendal or the Race penzoil is that alcohol doesn't tend to seperate in it like it does with other oils. I nevr tried the synthetic stuff..never could afford it.