What's your take on this:
https://www.google.com/patents/US6363923
A 15 cm diameter cylinder, spinning at ~80,000 RPM or more, driven like a turbo off exhaust gasses, used to centrifugally separate out the nitrogen from the oxygen in air and feed the oxygen to the engine, thereby effectively increasing the engine's volumetric efficiency. A 15 cm cylinder at ~80,000 RPM can supposedly achieve 33% oxygen content. As the engine works harder, the cylinder spins faster, and increases the percentage of oxygen in the intake air... so the harder you work your engine, the more effective cubic inches you've got.