You would never push part of the new intake charge through the exhaust valve opening because the cylinder would be under vacuum at the time. (mechanics.stackexchange.com)
These include Honda's i - VTEC system, which uses an advanced valve - control system to adjust valve overlap and therefore the amount of intake charge reentering the intake manifold. (cnet.com)
It has special properties which cool intake charge, enabling high boost levels, burns clean, and has some truly magic properties at the dragstrip. (mechanics.stackexchange.com)