but polishing can cause TOO smooth flow giving worse air/fuel mixing capabilities...
Also misted fuel sticks to smooth surfaces... where the roughness in casting stirs up the air against the walls so the fuel doesn't really have a chance to stick (as it's being blown of as air bounces off the rough-edged wall.)
If you spray whatever onto both a polished surface and a rough casted surface you'll notice the cast surface prevents it from pooling and becoming a liquid again... where the polished smooth surface allows all of the tiny droplets of water to re-connect and become more of a "puddle".
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