Cox (red can) Racing Fuel was 30% nitro. The Sig 35% nitro is what I use in all of my .020's, .049's and .061's. I've used stock low compression heads with one thin shim, one shim and high compression heads, Tee Dee cylinders and high compression heads on Babe Bees, they all run great on it. 35% nitro isn't high enough to change much except make a little more power, tame the needle to make it less sensitive, and allow better starting and a little higher temp so it keeps the glow head lit.<div>Until you get to 50% you don't see downsides like engine wear or difficult handling.</div><div>Chris... </div>