Byron's 20% is the preferred fuel of racers. Bashers use just about anything that says NITRO on it.<div></div><div>As far as the two engines, 3.3 or OS .18, I would recommend going with the OS. In the long run it'll hold up much better and is more consistent in holding a tune. Also, if you get a brand new motor, the best method, IMO, to break-in the engine is by heat cycling it. A proper break-in doesn't need aggressive movement of the piston. Keep the temps at about 200 degrees F for the first 4-5 tanks and remember to cool the engine in BDC between tanks for 10-15 minutes.</div><div></div><div>Hope this helps!</div>