Crucially two strokes have clever passges linking the crankcase to the cylinder, a 4 stroke dose not and so the only way for fuel to get into the upper cylinders is for it to go through the inlet valve. Also exhaust gasses will get past the rings on almost all model engines and piston ring blow by is exactly how the oil gets into the crankcase, but the amount blown past is only very small otherwise you are correct in saying it would be blasting out of the breather (although on my radial the rings and valves leak like sieves). On Laser engines there is a 2nd ring on the larger engines, an oil ring, to help 'pump' oil into the crankcase. its very effective and can be seen in operation if you ever take a laser apart and have a look inside the piston while moving it up and down the liner.

andi agree that on wet sump engines the oil is a coolant, and the same is true of a model two strokes and why the heli boys run alot of nitro. All that extra liquid cools the engine from within, but in the large volume of a radial crankcase i cant see that it will have any effect. Also throttle response may be worse due to a reduction of velocity through in the intake. Fianlly, has anyone tried running a 400 on the same oil as the evo engines? because the amount of oil that pours from my breather leads me to think that thr 18% they suggest is over the top. Iknow that the larger laser engines (120,150,180,240v,300v,360v) can be run on 10% oil without a problem (15% is recommended for safety though) and someone has even run a 150 on 5% oil without an issue. When i get time i will build one and run it in with 18% and keep reducing the oil until it dies just as an experiment. If anything will go it will be the big end bushes so it will be quite obvious!