Engines waste over 60% of their output via heat (cooling and exhaust). That makes them very very thermal inefficient. You will never get past 40% thermal efficiency let alone 90%. Also by careful design of the intake manifolds, it is entirely possible to EXCEED 100% VME on a NA engine. Infact race cars will all exceed this in the RPM range it is designed for, I would also expect that there are motorbikes that also exceed this. It is true to say however that a normal car will not pass 100% VME, but they will be quite high (upto 95% for modern car) And finally maxium VME is the point at which the engine developes the most torque.
Adding a turbo or supercharger does not make an engine more efficient. Superchargers (the roots type) are typically only around 50% efficient. Turbos are upto around 75% efficient.
