I have been starting to buy older engines on Ebay that are larger than recommended for my planes, .40 for the .25 planes, .61 for the .40 ect. to make up for the reduced power of my home made fuels. It adds weight, but the lower fuel consumption allows less fuel per flight, so it sort of evens out. I only use synthetic oil at 10%, so that increases the power slightly as well. With the lower power output and cooler operating temperatures I have no fears of ruining engines. If I ever do destroy one with too little oil (I haven't done so yet), the saving in fuel costs makes up for the occational loss of an engine, witch are mostly used anyway. For a competative flyer, cheap fuel mixes don't make sense, but for the fun flyer it is the only way to go.